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United States Patent Application 20170306245
Kind Code A1
Lindberg; Erkki October 26, 2017

METHOD AND APPARATUS FOR PROCESSING HYDROCARBONS

Abstract

A method and apparatus break down compounds, typically hydrocarbons, through oxidation. The compounds may still be in-situ or in a man-made location. The method for the processing of hydrocarbons within a location, provides for: a) introducing two electrodes into the location containing the hydrocarbons; b) providing connections between a voltage source and the electrodes; c) applying a voltage of a first polarity to the connections for a first period of time, under the control of a voltage controller; d) applying a voltage of a second, reversed, polarity to the connections for a second period of time, under the control of the voltage controller; e) repeating steps c) and d); steps c), d) and e) promoting the generation of free radicals thereby promoting a reduction in the length of the carbon chain and/or a reduction in the sulphur content and/or a reduction in the heavy metal content of the hydrocarbons.


Inventors: Lindberg; Erkki; (Sundsberg, FI)
Applicant:
Name City State Country Type

EKO HARDEN TECHNOLOGIES OY

Espoo

FI
Family ID: 1000002738438
Appl. No.: 15/532014
Filed: December 1, 2015
PCT Filed: December 1, 2015
PCT NO: PCT/EP2015/078242
371 Date: May 31, 2017


Current U.S. Class: 1/1
Current CPC Class: C10G 15/08 20130101; C10G 32/02 20130101; E21B 43/2401 20130101
International Class: C10G 15/08 20060101 C10G015/08; E21B 43/24 20060101 E21B043/24; C10G 32/02 20060101 C10G032/02

Foreign Application Data

DateCodeApplication Number
Dec 1, 2014GB1421261.7

Claims



1. A method for the processing of hydrocarbons within a location, the method comprising: a) introducing at least two electrodes into the location, the location containing the hydrocarbons; b) providing connections between a voltage source and the at least two electrodes; c) applying a voltage of a first polarity to the connections for a first period of time, under the control of a voltage controller; d) applying a voltage of a second, reversed, polarity to the connections for a second period of time, under the control of the voltage controller; e) repeating steps c) and d) a plurality of times; steps c), d) and e) promoting a reduction in the length of the carbon chain for one of more species present in the hydrocarbon and/or a reduction in the sulphur content of the hydrocarbons and/or a reduction in the heavy metal content of the hydrocarbons.

2. The method according to claim 1, wherein the hydrocarbons are within a volume of material at the location, with the volume of material being a matrix, the matrix being a mixture of liquids and solids, including the hydrocarbons and the surrounding rock.

3. The method according to claim 1, wherein the location is a man-made location for hydrocarbons extracted by human activity, the location being selected from the group: a location built to contain the hydrocarbons; a storage location; a transport location; a conduit through which hydrocarbons pass; a processing location.

4. The method according to claim 1, wherein the voltage is the voltage necessary to achieve a voltage of greater than 0.2V/m across the separation between the electrode of one potential and the electrode of a different potential which is closest to that electrode.

5. The method according to claim 1, wherein the voltage applied is in the form of a voltage pulse profile, the voltage pulse having a first section during which the voltage is at a maximum value, the voltage pulse profile having a first reversed section during which the voltage is at a maximum value, but of opposing polarity.

6. The method according to claim 1, wherein a defined current pulse profile is provided.

7. The method according to claim 6, wherein the defined current pulse profile includes a first section, a second section following on directly from the first section and a third section, wherein a fourth section intermediate the second section and the third section of the defined current pulse profile is also provided.

8. The method according to claim 6, wherein the defined current pulse profile has a first section having a start current value and an end current value, the first section start current value being zero and the first section end current value being the maximum current for the defined current pulse profile

9. The method according to claim 6, wherein the defined current pulse profile has a second section having a start current value and an end current value, the second section start current value being the maximum current for the defined current pulse profile, with the current declining between the second section start current value and the second section end current value, the second section end current value being a declined current value.

10. The method according to claim 9, wherein the defined current pulse continues at that declined current value for a fourth section of a current pulse profile, with the fourth section intermediate the second section and the third section of the defined current pulse profile.

11. The method according to claim 6, wherein the third section has a start current value and an end current value, the third section start current value is less than the maximum current for the defined current pulse profile and/or is the declined current value and the third section end current value is zero.

12. The method according to claim 6, wherein the defined current pulse profile has a first section which lasts for a first time period, the first time period being less than 0.5 ms.

13. The method according to claim 6, wherein the second section of the defined current pulse profile has a duration of between 10 ms and 500 ms.

14. The method according to claim 6, wherein the duration of the fourth section is greater than 500 ms.

15. The method according to claim 6, wherein the third section lasts for a third time period, the third time period being less than 0.5 ms.

16. The method according to claim 6, wherein the first section and/or second section have a current value in excess of the fourth section current value due to the discharge of the charge provided to the volume or material or a part of the volume of material during the immediately previous fourth reversed section.

17. The method according to claim 6, wherein the second section and/or the second reverse section include a current above the declined current value due to the voltage applied causing the one or more of the species to be treated and/or one or more components of the material, particularly of the matrix, to become charged according to the natural capacitance of the system.

18. The method according to claim 6, wherein the fourth section provides the, or a part of the, pulse during which the volume of material or a part of the volume of material becomes charged with the charge which contributes to the second reversed section of the current pulse profile.

19. The method according to claim 1, wherein the method promotes oxidisation by generating free radicals within the location.

20. The method according to claim 1, wherein the hydrocarbon has a first API value at a first time and the hydrocarbon has a second API value at a second time which is after the first time, the second API value being greater than the first API value, without the hydrocarbon being blended and/or mixed and/or contact with any further hydrocarbons of a different composition.

21. The method according to claim 1, wherein the hydrocarbon has a first viscosity value at a first time and the hydrocarbon has a second viscosity value at a second time which is after the first time, wherein the second viscosity value is less than the first viscosity value, without the hydrocarbon being blended and/or mixed and/or contact with any further hydrocarbons of a different composition.

22. The method according to claim 1, wherein the hydrocarbon has a first sulphur content at a first time and the hydrocarbon has a second sulphur content at a second time which is after the first time, the second sulphur content being less than the first sulphur content, without the hydrocarbon being blended and/or mixed and/or contact with any further hydrocarbons of a different composition.

23. The method according to claim 1, wherein the hydrocarbon has a first heavy metal content at a first time and the hydrocarbon has a second heavy metal content at a second time which is after the first time, the second heavy metal content being less than the first heavy metal content, without the hydrocarbon being blended and/or mixed and/or contact with any further hydrocarbons of a different composition.

24. An apparatus for the processing of hydrocarbons within a location, the apparatus including comprising: a) at least two electrodes, the at least two electrodes being introduced into the location, the location containing the hydrocarbons; b) connections between a voltage source and the at least two electrodes; c) a voltage controller for applying a voltage of a first polarity to the connections for a first period of time; d) the voltage controller applying a voltage of a second, reversed, polarity to the connections for a second period of time; e) the voltage controller repeating steps c) and d) a plurality of times; steps c), d) and e) promoting a reduction in the length of the carbon chain for one of more species present in the hydrocarbon and/or a reduction in the sulphur content of the hydrocarbons and/or a reduction in the heavy metal content of the hydrocarbons.

25. A method of calibrating the operating conditions to be used in a method of processing hydrocarbons within a location, the method comprising: a) introducing at least two electrodes into the location, the location containing a sample of the hydrocarbons for processing; b) providing connections between a voltage source and the at least two electrodes; c) applying a voltage of a first polarity to the connections for a first period of time, under the control of a voltage controller; d) applying a voltage of a second, reversed, polarity to the connections for a second period of time, under the control of the voltage controller; e) detecting the current arising within the sample or volume of material; f) varying one or more characteristics of the voltage; g) detecting the current arising within the sample or volume of material with the revised characteristics of the voltage; h) further varying one or more characteristics of the voltage until a defined current pulse profile is detected.

26. The method according to claim 25, wherein the sample is a sample taken from the location for which processing is to be applied and/or the sample is a sample of material believed to have or having equivalent properties to the volume of material.

27. The method according to claim 25, wherein the detected current varies according to one or more of the circuit resistance, the electrical conductivity of the material, the electrical conductivity of the matrix within the material, the electrical conductivity of the fluid within the material and/or one or more species within the material, and/or the number of electrodes provided within the material and/or the positions and/or separations of the electrodes within the material.

28. The method according to claims 25, wherein the defined current pulse profile includes a first section, a second section following on directly from the first section and a third section, wherein a fourth section intermediate the second section and the third section of the defined current pulse profile is also provided.

29. The method according to claim 25, wherein the defined current pulse profile has a first section having a start current value and an end current value, the first section start current value being zero and the first section end current value being the maximum current for the defined current pulse profile

30. The method according to claim 25, wherein the defined current pulse profile has a second section having a start current value and an end current value, the second section start current value being the maximum current for the defined current pulse profile, with the current declining between the second section start current value and the second section end current value, the second section end current value being a declined current value.

31. The method according to claim 30, wherein the defined current pulse continues at that declined current value for a fourth section of a current pulse profile, with the fourth section intermediate the second section and the third section of the defined current pulse profile.

32. The method according to claim 25, wherein the third section has a start current value and an end current value, the third section start current value is less than the maximum current for the defined current pulse profile and/or is the declined current value and the third section end current value is zero.
Description



[0001] This invention concerns improvements in and relating to the processing of matrices and/or the contents of matrices, in particular but not exclusively the treatment of geological structures, such as hydrocarbon containing reservoirs, and/or compounds, such as hydrocarbons either whilst within such structures and/or after extraction by human activity.

[0002] In a variety of situations, hydrocarbons are known to exist within the matrix formed by a geological structure. The geological structure may be a relatively shallow one such as encountered with some oil sands. The geological structure may be a relatively deep one beneath the surface, such as an offshore oil containing reservoir. Some forms of hydrocarbons, particularly light oils, are more readily extracted than other forms, such as heavy oils or bituminous hydrocarbons. Existing processing approaches can face difficulties in extracting such hydrocarbons or difficulties because of the costs of doing so.

[0003] Even once extracted by human activity, some hydrocarbons are more commercially valuable than others. Lighter oils which are closer to the high demand gasoline format of hydrocarbons are typically more valuable that heavier oils and/or sour oils which contain contaminants such as heavy metals or sulphur.

[0004] Existing approaches to the treatment of such compounds formed of less commercially valuable hydrocarbons are time consuming, expensive in terms of capital equipment and expensive in terms of operation, for instance power consumption or the need to blend the hydrocarbon with lighter oils.

[0005] The present invention has amongst its potential aims to provide a method and apparatus which offers a beneficial approach to breaking down compounds, typically hydrocarbons, through oxidation. This aim may relate to the compounds whilst still in-situ and/or after extraction by human activity from the location where they occurred.

[0006] The present invention has amongst its potential aims to provide a method and apparatus which allow a wider range of compounds, particularly hydrocarbons, to have commercial value or increased commercial value through the treatment of such hydrocarbons after extraction by human activity.

[0007] The present invention has amongst its potential aims to provide a low power consumption process and apparatus for the processing of geological structures, hydrocarbons below the surface of the ground or other hydrocarbon containing locations in matrix form, particularly to reduce the viscosity of the compounds present and/or to reduce the carbon chain length of the compounds present and/or to reduce the level of contamination present within those compounds, for instance contamination by sulphur and/or chlorides and/or heavy metals and/or water.

[0008] According to a first aspect of the invention there is provided a method for the processing of hydrocarbons within a location, the method including: [0009] a) introducing at least two electrodes into the location, the location containing the hydrocarbons; [0010] b) providing connections between a voltage source and the at least two electrodes; [0011] c) applying a voltage of a first polarity to the connections for a first period of time, under the control of a voltage controller; [0012] d) applying a voltage of a second, reversed, polarity to the connections for a second period of time, under the control of the voltage controller; [0013] e) repeating steps c) and d) a plurality of times; steps c), d) and e) promoting a reduction in the length of the carbon chain for one of more species present in the hydrocarbon and/or a reduction in the sulphur content of the hydrocarbons and/or a reduction in the heavy metal content of the hydrocarbons.

[0014] The processing of the hydrocarbons may be to reduce the viscosity of the hydrocarbons, for instance within the location. The processing of the hydrocarbons may be to reduce the size of the average hydrocarbon molecule present and/or the size of the larger hydrocarbon molecules present. The processing may be to convert one or more of the heavier hydrocarbons present to one or more light hydrocarbons. The processing may be to reduce the level of one or more contaminants in the hydrocarbons, such as the sulphur level and/or heavy metal level.

[0015] The hydrocarbons may be within a volume of material, with the volume of material being a matrix, for instance a matrix which is a mixture of liquid and solid, such as the hydrocarbons and the surrounding rock. This includes all situations where the hydrocarbons are present below the surface of the ground in a matrix awaiting extraction.

[0016] The location may be man-made location for hydrocarbons extracted by human activity. The location may be a location built to contain the hydrocarbons. The location may be a storage location. The location may be a transport location. The location may be a processing location. The location may be a location where the hydrocarbons occur naturally in-situ.

[0017] The location may be a tank or other form of container for hydrocarbons extracted by human activity. The tank or other form of container may be provided with an inlet for the hydrocarbons. The tank or other form of container may be provided with an outlet for the hydrocarbons. A pump or other means for moving the hydrocarbons may be provided, particularly to provide circulation and/or mixing of the hydrocarbons. The location may be a pre-existing location to which the method is applied, for instance a storage location. The location may be a location to which hydrocarbons are conveyed for the application of the method. The one or more electrodes may include one or more walls of the tank or other form of container, or parts thereof. The one or more electrodes may be provided within the tank or other form of container.

[0018] The location may be a conduit through which hydrocarbons pass after extraction by human activity. The conduit may be a pipe. The pipe may extend between a first site and a second site. The first site and the second site may be at least 1 km apart and may be at least 10 km apart. The first site may be a site at which hydrocarbons are extracted from an in-situ location. The second site may be a storage site or a processing site for hydrocarbons. The one or more electrodes may extend into the pipe, for instance across a part of the cross-section of the pipe. The one or more electrodes may be provided as a grid. The one or more electrodes may extend across a part of the cross-section of the pipe, potentially in different orientations along the length of the pipe. The location may be a naturally occurring location below ground. The location may be a geological structure, for instance one or more strata within a geological structure or parts thereof. The location may be a location at which hydrocarbons have been formed naturally below ground and/or a location to which naturally formed hydrocarbons have moved after extraction.

[0019] One or more outlets, preferably man made, may be provided to allow hydrocarbons to leave the geological structure, for instance one or more drilled extraction wells. One or more inlets, preferably man made, may be provided to allow one or more materials to be introduced to the geological structure, preferably to assist in the extraction of hydrocarbons.

[0020] The hydrocarbons may be introduced to the location, for instance by being extracted and removed to the location or for instance by being directed to the location by a prior process, such as flowing to the location.

[0021] The hydrocarbons may be already at the location below ground, for instance by being naturally occurring at the location and/or by being found at the location by investigations.

[0022] The hydrocarbons may be classified as heavy crude oil. The hydrocarbon may be classified as heavy crude oil due to having an API gravity of less than 22.3. The hydrocarbons may be classified as extra heavy crude oil. The hydrocarbons may be classified as extra heavy crude oil due to having an API of less than 10. Potentially the hydrocarbons may be classified as light crude oil. The hydrocarbon may be classified as light crude oil due to having an API of greater than 31.1 and/or due to originating from US and having an API of 37 to 42 and/or due to being non-US originating and having an API of 32 to 42 degrees. The hydrocarbon may be classified as medium crude oil. The hydrocarbon may be classified as medium crude oil due to having an API of 22.3 to 31.1. For reference, Brent crude has an API 38.06 and water has an API of 10.

[0023] The reduction of the length of the carbon chain for one or more species in the hydrocarbons may cause a change in the API value for the hydrocarbons and/or a change in viscosity for the hydrocarbons.

[0024] The hydrocarbon may have a first API value, for instance at a first time. The hydrocarbon may have a second API value, for instance at a second time which is after the first time. The time period between the first time and the second time may be between 20 hours and 2000 hours, potentially between 30 hours and 1000 hours, preferably between 60 hours and 400 hours and ideally between 75 hours and 300 hours. The second API value may be greater than the first API value. The second API value may be at least 25%, possibly at least 50%, potentially at least 75% and preferably at least 100% higher that the first API value.

[0025] The hydrocarbon may have a second API value which is greater than the first API value, without the addition of any further hydrocarbons having a greater API to the hydrocarbon being treated. The hydrocarbon may have a second API value which is greater than the first API value, without the hydrocarbon being blended and/or mixed and/or contact with any further hydrocarbons of a different composition.

[0026] The hydrocarbon may have a second API value which causes the hydrocarbon to be classified as a different grade of crude oil compare with the classification caused by the first API value. For instance, an extra heavy crude oil at the first time may be classified as a heavy crude oil at the second time. The API considerations are made at the same temperature at the first time and the second time.

[0027] The hydrocarbon may have a first viscosity value, for instance at a first time. The hydrocarbon may have a second viscosity value, for instance at a second time which is after the first time. The time period between the first time and the second time may be between 20 hours and 2000 hours, potentially between 30 hours and 1000 hours, preferably between 60 hours and 400 hours and ideally between 75 hours and 300 hours. The second viscosity value may be less than 60% the first viscosity value. The second viscosity value may be less than 30%, possibly less than 20%, potentially less than 15% and preferably at less than 10% of the first viscosity value.

[0028] The hydrocarbon may have a second viscosity value which is less than the first viscosity value, without the addition of any further hydrocarbons having a lower viscosity to the hydrocarbon being treated. The hydrocarbon may have a second viscosity value which is less than the first viscosity value, without the hydrocarbon being blended and/or mixed and/or contact with any further hydrocarbons of a different composition.

[0029] The hydrocarbon may have a second viscosity value which causes the hydrocarbon to be classified as a different, lighter, grade of crude oil compare with the classification caused by the first viscosity value. For instance, an extra heavy crude oil at the first time may be classified as a heavy crude oil at the second time. The viscosity considerations are made at the same temperature at the first time and the second time.

[0030] The reduction in the sulphur content of the hydrocarbons may arise together with a reduction in the carbon chain length for one or more species in the hydrocarbons.

[0031] The hydrocarbons may be classified as a sweet crude oil. The hydrocarbon may be classified as a sweet crude oil due to having a sulphur content of less than 0.5% by weight. The hydrocarbons may be classified as a sour crude oil. The hydrocarbons may be classified as a sour crude oil due to having a sulphur content of 0.5% or more by weight. The hydrocarbon may have a sulphur content at a first time of greater than 1%, possibly greater than 2%, potentially greater than 3% and even possibly greater than 4%.

[0032] The hydrocarbon may have a first sulphur content, for instance at a first time. The hydrocarbon may have a second sulphur content, for instance at a second time which is after the first time. The time period between the first time and the second time may be between 20 hours and 2000 hours, potentially between 30 hours and 1000 hours, preferably between 60 hours and 400 hours and ideally between 75 hours and 300 hours. The second sulphur content may be less than the first sulphur content. The second sulphur content may be 25% or more less than, possibly 50% or more less than, potentially 75% or more less than, and preferably 85% or more less than the first sulphur content.

[0033] The hydrocarbon may have a second sulphur value which is less than the first sulphur value, without the addition of any further hydrocarbons having a lower sulphur content to the hydrocarbon being treated. The hydrocarbon may have a second sulphur content which is less than the first sulphur content, without the hydrocarbon being blended and/or mixed and/or contact with any further hydrocarbons of a different composition.

[0034] The hydrocarbon may have a second sulphur content which causes the hydrocarbon to be classified as a sweet crude oil compared with a classification of sour crude oil caused by the first sulphur content value.

[0035] The reduction in the heavy metal content of the hydrocarbons may arise together with a reduction in the carbon chain length for one or more species in the hydrocarbons.

[0036] The hydrocarbon may have a first heavy metal content, for instance at a first time. The hydrocarbon may have a second heavy metal content, for instance at a second time which is after the first time. The time period between the first time and the second time may be between 20 hours and 2000 hours, potentially between 30 hours and 1000 hours, preferably between 60 hours and 400 hours and ideally between 75 hours and 300 hours. The second heavy metal content may be less than the first heavy metal content. The second heavy metal content may be 15% or more less than, possibly 25% or more less than, potentially 50% or more less than, and preferably 65% or more less than the first heavy metal content. The heavy metal content may consider one or more or all of: nickel, vanadium, copper cadmium or lead. The heavy metal content may consider, or may further consider in combination with the species above, one or more or all of e content with respect to cadmium, zinc, manganese, iron,

[0037] The hydrocarbon may have a second heavy metal content value which is less than the first heavy metal content value, without the addition of any further hydrocarbons having a lower heavy metal content to the hydrocarbon being treated. The hydrocarbon may have a second heavy metal content which is less than the first heavy metal content, without the hydrocarbon being blended and/or mixed and/or contact with any further hydrocarbons of a different composition.

[0038] The two or more electrodes, particularly when provided in a naturally occurring location such as a geological structure, may have a length of over 25 m, for instance over 50 m, possibly over 100 m and potentially over 250 m. The two or more electrodes, particularly when provided in a naturally occurring location such as a geological structure, may have a length of less than 2000 m, for instance less than 1000 m, possibly less than 500 m and potentially less than 250 m.

[0039] The two or more electrodes may have a length of over 0.25 m, for instance over 1 m, possibly over 5 m and potentially over 10 m. The two or more electrodes may have a length of less than 30 m, for instance less than 15 m, possibly less than 10 m and potentially less than 5 m.

[0040] The two or more electrodes, particularly when provided in a storage location such as a tank or other container, may have a length of over 1 m, for instance over 2 m, possibly over 3 m and potentially over 5 m. The two or more electrodes, particularly when provided in a storage location such as a tank or other container, may have a length of less than 20 m, for instance less than 10 m, possibly less than 7 m and potentially less than 5 m.

[0041] The two or more electrodes, particularly when provided in a conduit such as a pipe, may have a length of over 0.1 m, for instance over 0.3 m, possibly over 0.5 m and potentially over 1 m. The two or more electrodes, particularly when provided in a conduit such as a pipe, may have a length of less than 2 m, for instance less than 1 m, possibly less than 0.75 m and potentially less than 0.5 m.

[0042] The two or more electrodes may be of titanium, particularly titanium provided with a mixed metal oxide surface or coating. The two or more electrodes may be of steel.

[0043] The two or more electrodes may be spaced along the length of the location. The two or more electrodes may be spaced along the width of a location. The length and width of the location may be provided with an array of electrodes, for instance a regular array of electrodes. The spacing of the electrodes may be a common spacing between one electrode and the next across the width of the location. The spacing of the electrodes may be a common spacing across the length of the location. The spacing may be the same across the width as along the length of the location.

[0044] The spacing may be lower or higher across the width of the location when compared with the length of the location.

[0045] More electrodes may be provided in one or more parts of the location being treated compared with one or more other parts. The one or more parts may include the edges of the location being treated. The one or more parts may include the central 30% of the location being treated, considered by volume or considered by distance relative to the distance between one electrode at one extremity of the location and the electrode further away from that electrode. The one or more other parts may include the edges of the location being treated. The one or more other parts may include the central 30% of the location being treated, considered by volume or considered by distance relative to the distance between one electrode at one extremity of the location and the electrode further away from that electrode.

[0046] The electrodes, particularly when provided in a naturally occurring location such as a geological structure, may have a spacing greater than 25 m, for instance greater than 50 m, possibly greater than 100 m and potentially greater than 250 m. The electrodes, particularly when provided in a naturally occurring location such as a geological structure, may have a spacing less than 5000 m, for instance less than 2500 m, possibly less than 1000 m and potentially less than 500 m.

[0047] The electrodes may have a spacing greater than 1 m, for instance greater than 2 m, possibly greater than 5 m and possibly greater than 10 m. The electrodes may have a spacing less than 50 m, for instance less than 25 m, possibly less than 15 m and possibly less than 10 m.

[0048] The electrodes, particularly when provided in a storage location such as a tank or other container, may have a spacing greater than 0.1 m, for instance greater than 0.5 m, potentially greater than 2 m and possibly greater than 5 m. The electrodes, particularly when provided in a storage location such as a tank or other container, may have a spacing less than 15 m, for instance less than 10 m, potentially less than 5 m and possibly less than 2 m.

[0049] The electrodes, particularly when provided in a conduit such as a pipe, may have a spacing of greater than 0.01 m, for instance greater than 0.05 m, possibly greater than 0.1 m and potentially greater than 0.3 m. The electrodes, particularly when provided in a conduit such as a pipe, may have a spacing of less than 1 m, for instance less than 0.5 m, possibly less than 0.3 m and potentially less than 0.2.

[0050] The electrodes may have an extent into the depth, particularly when provided in a naturally occurring location such as a geological structure, of greater than 10 m, for instance greater than 50 m, possibly greater than 100 m and potentially greater than 250 m. The electrodes may have an extent into the depth, particularly when provided in a naturally occurring location such as a geological structure, of less than 1000 m, for instance less than 500 m, possibly less than 200 m and potentially less than 100 m.

[0051] The electrodes may have an extent into the depth for instance greater than 0.7 m, possibly greater than 2 m and potentially greater than 5 m. The electrodes may have an extent into the depth of less than 10 m, for instance less than 5 m, possibly less than 2 m and potentially less than 1 m.

[0052] The electrodes may have an extent into the depth, particularly when provided in a storage location such as a tank or other container, of greater than 0.5 m, for instance greater than 1.5 m, possibly greater than 4 m and potentially greater than 8 m. The electrodes may have an extent into the depth, particularly when provided in a storage location such as a tank or other container, of less than 20 m, for instance less than 10 m, possibly less than 5 m and potentially less than 2 m.

[0053] The electrodes may have an extent into the depth, particularly when provided in a conduit such as a pipe, of greater than 0.1 m, for instance greater than 0.5 m, possibly greater than 1 m and potentially greater than 2 m. The electrodes may have an extent into the depth, particularly when provided in a conduit such as a pipe, of less than 3 m, for instance less than 2 m, possibly less than 1 m and potentially less than 0.5 m.

[0054] The electrodes may have an extent into the depth of the location which is at least 20% of the depth of the location being treated, more preferably at least 50% of the depth of the location being treated.

[0055] A gap may exist between the top of the electrodes and the surface of the structure they are provided in. The gap may be bridged by the electrical conductor, for instance wire, used to connect the electrodes to the surface and/or power supply.

[0056] The electrodes may be generally vertically provided, for instance +/-20 degrees to the vertical, ideally +/-5 degrees to the vertical. The generally vertically provided electrode may provide only a section of the overall electrode. The generally vertically provided electrode may be present in combination with a generally horizontal section of electrode to provide an overall electrode. Inclined, curved, spiral and other shapes for the electrode may be provided. For instance a drill, subsequently used as an electrode, or an electrode inserted into a drill hole may extend down into the location and then turn and extend out into the location with various directions and inclinations for different sections.

[0057] The electrodes may be inserted into apertures formed within the volume of material. The apertures may be formed by drilling into the volume of material. The drills may subsequently be used as the electrodes. The apertures may be formed by driving or otherwise forcing an element into the volume of material. The elements may subsequently be used as the electrodes.

[0058] One or more material may be added to the aperture, before and/or during and/or after drilling or driving or forcing. The one or more materials may increase the conductivity between the electrodes and the volume of material compared with the conductivity when the one or more materials are absent.

[0059] One or more pairs of alternative orientation electrodes may be provided. One or more sets of electrodes of alternative orientation may be provided. The alternative orientation may be horizontal +/-30 degrees, preferably +/-20 degrees and ideally +/-5 degrees. Such pairs or sets of electrodes may be provided in addition to the other pairs or sets of electrodes.

[0060] The alternative orientation pairs or sets of electrodes may be provided with connections and/or voltage pulse profiles and/or defined current pulse profiles and/or other characteristics as defined elsewhere for the pairs of electrodes or sets of electrodes.

[0061] The electrodes, particularly when provided in alternative orientations, may be positioned within the volume of material, for instance using gravity, for instance by allowing the electrodes to settle within the location.

[0062] The electrodes, particularly when provided in alternative orientations, may be flexible electrodes. The flexible electrodes may be wires and/or cables and/or flexible rods. The electrodes, particularly the flexible electrodes, may be bare metal electrodes and/or be without any insulating coating or cover.

[0063] The connections may include the connection of the voltage source to two or more electrodes, those two or more electrodes forming a first set of electrodes. The voltage controller may provide a first set of operating conditions to the first set of electrodes.

[0064] The method may further include providing connections between the voltage source and two or more second set electrodes. The voltage controller may provide a second set of operating conditions to the second set of electrodes.

[0065] The method may further include providing connections between the voltage source and one of more still further sets electrodes. The voltage controller may provide a still further set of operating conditions to each of the still further sets of electrodes.

[0066] Each of the sets of operating conditions may be different from each of the other sets of operating conditions. Two or more of the operating conditions may be the same as each other. The operating conditions may include the voltage pulse profile applied, including the voltage pulse profile during different component parts of the voltage pulse profile, the magnitude of the pulse over its full cycle and during the different component parts and the duration of the full cycle and each of the component parts and the sequence of the component parts. The operating conditions may include one or more of: the voltage pulse profile applied; the voltage pulse profile during one or more or all of the different component parts of the voltage pulse profile; the magnitude of the pulse over its full cycle and/or during one or more or all of the different component parts; the duration of the full cycle and/or one or more or each of the component parts; or the sequence of the component parts.

[0067] Two or more of the sets of operating conditions may be the same except for the start time of the voltage pulse profile. The start time of the voltage pulse profile may be offset with respect to one or more or all of the other sets of operating conditions. The second set of operating conditions may be offset in time with respect to the start of its voltage pulse profile compared with the start of the voltage pulse profile of the first set of operating conditions. The still further sets of operating conditions may be provided with their own further offsets, potentially including an offset value for one of the still further sets of operating conditions which cause it to have the same phase as the first set of operating conditions. One or more of the still further sets of operating conditions may have a phase matching the first set of operating conditions. One or more of the still further sets of operating conditions may have a phase matching the second set of operating conditions. One or more of the still further sets of operating conditions may have a phase matching one of the other still further sets of operating conditions.

[0068] The first set of electrodes may include electrodes extending across the width of the location in a first set of positions, for instance in a row. The first set of electrodes may include electrodes extending across the width of the location at a second set of positions, for instance a second row. The first and second positions may be such that there are no intervening electrodes from other sets of electrodes. The first and second positions may be rows, relative to the length of the location, ideally with no rows of electrodes from one or more other sets of electrodes between them. In particular, the first set of electrodes may have a first row of electrodes and a second row of electrodes adjacent one another.

[0069] A second set of electrodes may be provided in addition to the first set of electrodes. The second set of electrodes may include electrodes extending across the width of the location in a second set of positions, for instance in a row. The second set of electrodes may include electrodes extending across the width of the location at a second set of positions, for instance a second row. The first and second positions may be such that there are no intervening electrodes from other sets of electrodes. The first and second positions may be rows, relative to the length of the location, ideally with no rows of electrodes from one or more other sets of electrodes between them. In particular, the second set of electrodes may have a first row of electrodes and a second row of electrodes adjacent one another. The second set of electrodes may be provided to one side, for instance relative to the length of the location, the first of the still further sets of electrodes may be provided to the other side. The various still further sets of electrodes may be provided in equivalent arrangements relative to one another.

[0070] In a preferred form, the first set of electrodes may be provided in two parallel rows, followed by the second set of electrodes in two parallel rows, followed by a further first set of electrodes in two parallel rows, followed by a further second set of electrodes in two parallel rows, potentially with one or more further repeats of this arrangement. Within each set of electrodes, it is preferred that one row is of a first polarity and the other row is of a different polarity. Corresponding rows in different sets of electrodes may be provided at the same polarity at the same time.

[0071] The voltage source may be connected to a mains power supply. The voltage source may be connected to a discrete power supply, for instance a power supply specific to the method and/or specific to the geographical location at which the method is conducted. The voltage source may be an AC voltage source or a DC voltage source. The voltage source may step down the voltage to the level required for the method. A constant voltage output may be provided.

[0072] The voltage may be the voltage necessary to achieve a voltage of greater than 0.2V/m across the separation between the electrode of one potential and the electrode of a different potential which is closest to that electrode. A voltage greater than 0.4V/m may be so provided. A voltage greater than 0.8V/m may be so provided. The voltage drop provided may be greater than 1V/m, for instance greater than 1.5V/m, possibly greater than 2V/m or potentially greater than 3V/m. A voltage greater than 0.4V/m may be so provided. A voltage less than 10V/m may be so provided. The voltage drop provided may be less than 8V/m, for instance less than 66V/m, possibly less than 4V/m or potentially less than 3V/m.

[0073] The voltage controller may determine the voltage applied to one of the at least two electrodes. The voltage controller may determine the voltage applied to the electrodes in the first position in a set of electrodes, including the first set and/or second set and/or one or more of the still further sets. The voltage controller may apply a zero voltage or a different voltage to the other of the at least one electrodes. The voltage controller may apply a zero voltage or a different voltage to the electrodes in the second position in a set of electrodes, including the first set and/or second set and/or one of more of the still further sets. A zero voltage or a voltage of a different polarity may be applied to the other of the at least one electrodes. A zero voltage or a voltage of a different polarity may be applied to the electrodes in the second position in a set of electrodes.

[0074] The voltage controller may determine the voltage applied to the first position electrodes in a second set of electrodes. The voltage controller may apply a voltage and/or a polarity to the first position electrodes in the second set of electrodes which is different to the second position electrodes in the first set of electrodes. The voltage controller may determine the voltage applied to the first position electrodes in one or more or all of the still further sets of electrodes. The voltage controller may apply a voltage and/or a polarity to the first position electrodes in the one or more or all still further sets of electrodes which is different to the second position electrodes in the adjacent set of electrodes. In a preferred form, one row of electrodes is at a first voltage and/or first polarity, with the adjacent row of electrodes on one or both sides at a second voltage and/or polarity and/or a third voltage and/or polarity respectively. The second voltage and/or polarity and the third voltage and/or polarity may be the same. A voltage difference and/or polarity difference may be provided between all adjacent position electrodes.

[0075] The voltage applied may be in the form of a voltage pulse profile. The voltage pulse may have a first section during which the voltage is at a maximum value. The voltage pulse profile may have a second section during which the voltage is at a maximum value, but of opposing polarity. The voltage pulse profile may be a square wave profile. The duration of the first section and the duration of the second section are preferably the same.

[0076] In instances were transport of one or more parts of the matrix and/or one or more of the species being treated and/or one or more of the reaction products from the treatment of the one or more species is desired, then the first section and the second section may have different durations.

[0077] The first section and the second section are preferably adjacent one another. Preferably the second section is followed by a further first section. Preferably the further first section is followed by a further second section. Preferably alternating repeats of the first section and the second section are provided.

[0078] In one embodiment of the invention, a third section is provided between the first section and the start of the second section. A fourth section may be provided between the second section and the start of a further first section. The sequence of first section, third section and second section may be repeated. The sequence of second section, fourth section and further first section may be repeated. The third section and/or fourth section may be a zero voltage section.

[0079] The first section and/or the second section may have a duration of between 1 and 500 ms, for instance between 10 ms and 500 ms, more particularly between 20 and 200 ms. The third section and/or fourth section may have a duration of 0.5 ms to 50 ms.

[0080] The voltage controller may provide a voltage, particularly a voltage pulse profile, to the one or more pairs of electrodes so as to provide and/or seek to provide a defined current pulse profile. The voltage, particularly the voltage pulse profile, may be determined through a calibration method, for instance a calibration method according to the third aspect of the invention.

[0081] The defined current pulse profile may include a first section. The defined current pulse profile may include a second section, preferably following on directly from the first section. The defined current pulse profile may include a third section, preferably following on directly from the second section or following on from a fourth section. The defined current pulse may include a first reversed section. The defined current pulse profile may include a second reversed section, preferably following on directly from the first reversed section. The defined current pulse profile may include a third reversed section, preferably following on directly from the second reversed section. The defined current pulse profile may include repeats of the sections, particularly with the first section following on directly from the third reversed section.

[0082] The first reversed section may have the equivalent profile shape but with a reversed current direction compared with the first section. The second reversed section may have the equivalent profile shape but with a reversed current direction compared with the second section. The third reversed section may have the equivalent profile shape but with a reversed current direction compared with the third section.

[0083] The first section may have a start current value and an end current value. The first section start current value may be zero. The first section end current value may be the maximum current for the defined current pulse profile. The first section may last for a first time period. The first time period may be less than 0.5 ms, more preferably less than 0.1 ms and ideally less than 0.05 ms. The first reverse section may be similarly provided.

[0084] The second section may have a start current value and an end current value. The second section start current value may be the maximum current for the defined current pulse profile. The current may decline between the start current value and the end current value. The end current value may be a declined current value. The declined current value may be the current value which occurs with the prolonged, for instance greater than 500 ms, application of the voltage in the corresponding part of the voltage pulse profile. The declined current value may be the value the current declines to, from the maximum current value, with the passage of time but represents a steady state current reached after a period of time. The decline current value may continue at that declined current value for a fourth section of a current pulse profile, with the fourth section intermediate the second section and the third section of the defined current pulse profile.

[0085] In the defined current pulse profile, a fourth section may be preferred. The fourth section may provide the, or a part of the, pulse section during which the volume of material or a part of the volume of material becomes charged. The fourth section may provide the charge which contributes to the second reversed section of the current pulse profile, for instance by contributing to the higher value of the current during the second reversed section of the current pulse profile. The fourth section may provide the charge which contributes to the first reversed section of the current pulse profile having a higher maximum current value that the minimum current value of the second reversed section, for instance by contributing to the higher value of the current during the first reversed section of the current pulse profile.

[0086] In the defined current pulse profile, a fourth reversed section may be preferred. The fourth reversed section may provide the, or a part of the, pulse section during which the volume of material or a part of the volume of material becomes charged. The fourth reversed section may provide the charge which contributes to the second section of the current pulse profile, for instance by contributing to the higher value of the current during the second section of the current pulse profile. The fourth reversed section may provide the charge which contributes to the first section of the current pulse profile having a higher maximum current value that the minimum current value of the second section, for instance by contributing to the higher value of the current during the first section of the current pulse profile.

[0087] The first section and/or second section may have a current value in excess of the fourth section current value due to the discharge of the charge provided to the volume or material or a part of the volume of material during the immediately previous fourth reversed section.

[0088] The first reversed section and/or second reversed section may have a current value in excess of the fourth reversed section current value due to the discharge of the charge provided to the volume or material or a part of the volume of material during the immediately previous fourth section.

[0089] In the defined current pulse profile it may be provided that no fourth section is present. It is preferred that the end of the decline in current represents the transition point to the third section of the defined current pulse profile.

[0090] The second section may have a generally elliptical shape, with an initial rapid decrease in current and then decreasing rate of current decline down to the declined current value. The second reverse section may be similarly provided. Potentially there is no fourth reverse section between the second reverse section and the third reverse section in the defined current pulse profile.

[0091] The second section of the defined current pulse profile and/or the second reverse section of the defined current profile may have a duration of 1 ms or greater, for instance between 1 ms and 500 ms, or for instance between 10 ms and 500 ms, more particularly between 20 and 200 ms.

[0092] The fourth section and the fourth reverse section may be absent from the defined current pulse profile, but may be present with a duration of less than 5ms and more preferably less than 1 ms and ideally less than 0.5 ms. In an alternative embodiment, the fourth section may have a duration of at least 1 ms, potentially of at least 15 ms, preferably at least 50 ms, optionally at least 100 ms and potentially at least 500 ms. For instance, the duration may be between 1 ms and 500 ms, or for instance between 10 ms and 500 ms, more particularly between 20 and 200 ms.

[0093] The third section may have a start current value and an end current value. The third section start current value may be less than the maximum current for the defined current pulse profile and/or may be the declined current value. The third section end current value may be zero. The third section may last for a third time period. The third time period may be less than 0.5 ms, more preferably less than 0.1 ms and ideally less than 0.05 ms. The third reverse section may be similarly provided.

[0094] The second section and/or the second reverse section may include a current above the declined current value due to the voltage applied causing the one or more of the species to be treated and/or one or more components of the material, particularly of the matrix, to become charged according to the natural capacitance of the system.

[0095] The reduction in current between the start and end of the second section may cause and/or be indicative of the formation of free radicals within the material, preferably with these free radicals being involved in the oxidation reactions which treat one or more of the species.

[0096] The repeating of steps c) and d) a plurality of times, may include at least 1000 repetitions, more preferably at least 10,000 repetitions and ideally at least 500,000 repetitions. The repeating of steps c) and d) a plurality of times, may include more than 5 million repetitions, possibly more than 10 million repetitions and even possibly more than 25 million repetitions.

[0097] The method may include one or more further processing steps. The one or more further steps may be performed in parallel with step e) of the method. The one or more further steps may be provided subsequent to part or all of step e) of the method. For instance, one or more further processing steps may be provided which extract hydrocarbons from the location. Such extraction may occur in parallel with step e). Such extraction may occur after step e) has been in progress for a period of time but before step e) ends. Such extraction may occur after step e) has ended. Step e) may be stopped whilst one or morefurther processing steps are provided, but step e) may be recommenced. Step e) may recommence after the one or more further processing steps have stopped or whilst they continue. One or more cycles of such steps may be provided.

[0098] The one or more further steps may include extracting hydrocarbons from the location. The extraction may be provided by pumping the hydrocarbons from the location and/or by displacing the hydrocarbons from the location and/or by the application of heat to the hydrocarbons and/or by the application of pressure to the hydrocarbons.

[0099] The hydrocarbons may be extracted from the in-situ location where they formed or where they accumulated below ground. The hydrocarbons may be stored at the extraction location or within 1 km thereof. The hydrocarbons may be transported from the storage location to a further storage location and/or processing location. The hydrocarbons may be transported to a still further storage location and/or further processing location. The method of processing the hydrocarbons at a location may be applied to the hydrocarbons whilst in-situ and/or during transportation to the extraction location and/or at the extraction location and/or during transportation to the storage location and/or at the storage location and/or during transportation to the further storage location and/or processing location and/or during transportation from the further storage location and/or processing location to a still further storage location and/or further processing location.

[0100] The method may promote oxidisation by generating free radicals within the location. The method may generate the free radicals at the surface of the solid species within the matrix forming the location, with respect to one or more or all of those solid species within the matrix.

[0101] Preferably water is present in and/or is added to the location and/or the volume of material and/or the hydrocarbons. Preferably the hydrocarbons are in contact with and/or in proximity with water. Preferably the hydrocarbons contain water, for instance droplets of water dispersed in the hydrocarbons, or vice versa.

[0102] Preferably solids are present in and/or are added to the location and/or the volume of material and/or the hydrocarbons. Preferably the hydrocarbons are in contact with and/or in proximity with solid material. Preferably the hydrocarbons contain solid material, for instance solid particles dispersed in the hydrocarbons.

[0103] Preferably the method has one or more or all of the following effects upon the matrix and/or upon one or more of the species: [0104] breaking down one or more species present to one or more smaller species, preferably with reduced toxicity or reduced other undesirable characteristics and/or with more mobility within the matrix and/or with greater solubility; [0105] reducing the level of contaminants present in the liquid, such as water, drawn off the method, for instance through breakdown of those compounds or changing their form; [0106] changing the surface chemistry of the matrix and/or one or more of the species, for instance in terms of their physical chemistry and/or in terms of the ions or other species present at the surface and/or the charge level of the surface, for instance so as to promote better settling of the materials or species within it and/or flocculation of the materials or species within it; [0107] reduction in the volume of the material compared with its untreated form, for instance by more than 30%, more than 40% or even 50% or more.

[0108] Preferably the method has one or more or all of the following effects upon the matrix and/or one or more of the species between a first time at the start of the method's application and a second time after the method has been applied: [0109] a reduction in the concentration of the C40 or more carbon atoms hydrocarbons by 20% or more, potentially by 35% or more, preferably by 50% or more, ideally by 70% or more; [0110] an increase in the concentration of the C8 to C30 hydrocarbons by more than 100%, potentially by more than 200%, preferably by more than 500% and ideally by more than 700%; [0111] an increase in the concentration of the less than C8 hydrocarbons (or organic compounds) by more than 25%, potentially by more than 50%, preferably by more than 100% and ideally by more than 200%; [0112] a reduction in the concentration of the C8 or greater hydrocarbons by 10% or more, potentially 20% or more, preferably by 30% or more and ideally by 40% or more.

[0113] The time period between the first time period and the second time period may be between 20 hours and 2000 hours, potentially between 30 hours and 1000 hours, preferably between 60 hours and 400 hours and ideally between 75 hours and 300 hours.

[0114] The voltage pulse profile may generate electro-osmotic forces in a first direction, and then when the polarity is reversed, in the opposite direction for any one species present (depending upon its charge). The method may cause the charged contents of the pore water to move back and forward with the polarity changes. The method may cause freshly formed oxygen and hydroxyl free radicals formed in these electrochemical reactions to move back and forth. The method may promote the involvement of the free radicals in the oxidisation of the compounds present. The method may cause the free radicals to cause hydrocarbon chains to breakdown into lighter fractions and form carbon dioxide and water as by products. Water may be present and/or added to participate in formation of oxygen and/or hydroxyl free radicals by the electrochemical reactions.

[0115] The voltage pulse profile, particularly when the physical nature of the matrix is one with a moderate or low degree of compaction, means that the electrophoretic forces generated (which generally oppose the direction of electro-osmotic forces) cause small amounts of movement by the particulate material.

[0116] Optionally the method includes control of the pH of the material, particularly the liquid phase. Preferably the pH is greater than 3, ideally greater than 4. The method of control may include the introduction of pH controlling compounds or species to the electrodes. The method preferably seeks to maintain the pH within the range at which any heavy metals to be treated according to the method remain as heavy metal ions and so are soluble. pH control may be provided by treatment of water extracted from and reintroduced to and/or introduced to the electrodes. A perforated barrier, such as a tube, may be provided around each electrode. The barrier may define a reservoir of water between the electrode and the material which is of the correct pH.

[0117] According to a second aspect of the invention there is provided apparatus for the processing of hydrocarbons within a location, the apparatus including: [0118] a) at least two electrodes, the at least two electrodes being introduced into the location, the location containing the hydrocarbons; [0119] b) connections between a voltage source and the at least two electrodes; [0120] c) a voltage controller for applying a voltage of a first polarity to the connections for a first period of time; [0121] d) the voltage controller applying a voltage of a second, reversed, polarity to the connections for a second period of time; [0122] e) the voltage controller repeating steps c) and d) a plurality of times; steps c), d) and e) promoting a reduction in the length of the carbon chain for one of more species present in the hydrocarbon and/or a reduction in the sulphur content of the hydrocarbons and/or a reduction in the heavy metal content of the hydrocarbons. The second aspect of the invention includes apparatus and component parts therefore for implementing and/or providing each of the features, options and possibilities defined elsewhere within this document, and in particular within the first aspect of the invention.

[0123] According to a third aspect of the invention there is provided a method of calibrating the operating conditions to be used in a method of processing hydrocarbons within a location, the method including: [0124] a) introducing at least two electrodes into the location, the location containing a sample of the hydrocarbons for processing; [0125] b) providing connections between a voltage source and the at least two electrodes; [0126] c) applying a voltage of a first polarity to the connections for a first period of time, under the control of a voltage controller; [0127] d) applying a voltage of a second, reversed, polarity to the connections for a second period of time, under the control of the voltage controller; [0128] e) detecting the current arising within the sample or volume of material; [0129] f) varying one or more characteristics of the voltage; [0130] g) detecting the current arising within the sample or volume of material with the revised characteristics of the voltage; [0131] h) further varying one or more characteristics of the voltage until a defined current pulse profile is detected.

[0132] The sample could be a sample taken from the location for which processing is to be applied. The sample could be a sample of material believed to have or having equivalent properties to the volume of material.

[0133] The detected current may vary according to one or more of the circuit resistance, the electrical conductivity of the material, the electrical conductivity of the matrix within the material, the electrical conductivity of the fluid within the material and/or one or more species within the material, and/or the number of electrodes provided within the material and/or the positions and/or separations of the electrodes within the material.

[0134] The defined current pulse profile sought may include a first section. The defined current pulse profile may include a second section, preferably following on directly from the first section. The defined current pulse profile may include a third section, preferably following on directly from the second section or following on from a fourth section. The defined current pulse may include a first reversed section. The defined current pulse profile may include a second reversed section, preferably following on directly from the first reversed section. The defined current pulse profile may include a third reversed section, preferably following on directly from the second reversed section. The defined current pulse profile may include repeats of the sections, particularly with the first section following on directly from the third reversed section.

[0135] The first reversed section may have the equivalent profile shape but with a reversed current direction compared with the first section. The second reversed section may have the equivalent profile shape but with a reversed current direction compared with the second section. The third reversed section may have the equivalent profile shape but with a reversed current direction compared with the third section.

[0136] The first section may have a start current value and an end current value. The first section start current value may be zero. The first section end current value may be the maximum current for the defined current pulse profile. The first section may last for a first time period. The first time period may be less than 0.5 ms, more preferably less than 0.1 ms and ideally less than 0.05 ms. The first reverse section may be similarly provided.

[0137] The second section may have a start current value and an end current value. The second section start current value may be the maximum current for the defined current pulse profile. The current may decline between the start current value and the end current value. The end current value may be a declined current value. The declined current value may be the current value which occurs with the prolonged, for instance greater than 500 ms, application of the voltage in the corresponding part of the voltage pulse profile. The declined current value may be the value the current declines to, from the maximum current value, with the passage of time but represents a steady state current reached after a period of time. The decline current value may continue at that declined current value for a fourth section of a current pulse profile, with the fourth section intermediate the second section and the third section of the defined current pulse profile.

[0138] In the defined current pulse profile, a fourth section may be preferred. The fourth section may provide the, or a part of the, pulse section during which the volume of material or a part of the volume of material becomes charged. The fourth section may provide the charge which contributes to the second reversed section of the current pulse profile, for instance by contributing to the higher value of the current during the second reversed section of the current pulse profile. The fourth section may provide the charge which contributes to the first reversed section of the current pulse profile having a higher maximum current value that the minimum current value of the second reversed section, for instance by contributing to the higher value of the current during the first reversed section of the current pulse profile.

[0139] In the defined current pulse profile, a fourth reversed section may be preferred. The fourth reversed section may provide the, or a part of the, pulse section during which the volume of material or a part of the volume of material becomes charged. The fourth reversed section may provide the charge which contributes to the second section of the current pulse profile, for instance by contributing to the higher value of the current during the second section of the current pulse profile. The fourth reversed section may provide the charge which contributes to the first section of the current pulse profile having a higher maximum current value that the minimum current value of the second section, for instance by contributing to the higher value of the current during the first section of the current pulse profile.

[0140] The first section and/or second section may have a current value in excess of the fourth section current value due to the discharge of the charge provided to the volume or material or a part of the volume of material during the immediately previous fourth reversed section.

[0141] The first reversed section and/or second reversed section may have a current value in excess of the fourth reversed section current value due to the discharge of the charge provided to the volume or material or a part of the volume of material during the immediately previous fourth section.

[0142] In the defined current pulse profile it may be provided that no fourth section is present. It may be preferred that the end of the decline in current represents the transition point to the third section of the defined current pulse profile.

[0143] The second section may have a generally elliptical shape, with an initial rapid decrease in current and then decreasing rate of current decline down to the declined current value. The second reverse section may be similarly provided. Potentially there is no fourth reverse section between the second reverse section and the third reverse section in the defined current pulse profile.

[0144] The second section of the defined current pulse profile and/or the second reverse section of the defined current profile may have a duration of between 10 ms and 500 ms, more particularly between 20 and 200 ms.

[0145] The fourth section and the fourth reverse section may be absent from the defined current pulse profile, but may be present with a duration of less than 5 ms and more preferably less than 1 ms and ideally less than 0.5 ms.

[0146] The calibration method may vary the voltage to reduce the duration of and/or eliminate the presence of the fourth section and/or provide a desired duration. The desired duration may be the duration which provides for a given degree of charging of the location and preferably the matrix therein or the surfaces of the matrix. The given degree of charging may be at least 70% of the natural capacitance, more preferably at least 80% and ideally at least 90%. The natural capacitance may be considered relative to the electrical potential being applied across the matrix and/or the separation of the electrodes and/or the distance from the electrodes.

[0147] The calibration method may vary the voltage to ensure that the declined current value is reached.

[0148] The calibration method may vary one or more of the following when varying the voltage: the duration of one or more of the above defined sections for the voltage pulse profile; the magnitude of the voltage; the polarity of the voltage; the shape of the voltage pulse profile.

[0149] The calibration method may provide iterative changes to the voltage and consider the current pulse profile arising, with the iterative changes continuing until the defined current pulse profile is reached.

[0150] The third section may have a start current value and an end current value. The third section start current value may be less than the maximum current for the defined current pulse profile and/or may be the declined current value. The third section end current value may be zero. The third section may last for a third time period. The third time period may be less than 0.5 ms, more preferably less than 0.1 ms and ideally less than 0.05 ms. The third reverse section may be similarly provided.

[0151] The first and/or second and/or third aspects of the invention may include any of the features, options or possibilities set out elsewhere in this application, including with the other aspects of the invention and the description which follows.

[0152] The invention will now be described, by way of example only, and with reference to the accompanying drawings in which:

[0153] FIG. 1 is a schematic perspective view of a volume of matrix and the hydrocarbon compounds contained therein being treated according to an embodiment of the invention;

[0154] FIG. 2a is an illustration of the voltage pulse shape applied to the electrodes in the matrix over a series of pulses, where the voltage pulse profile does not provide the net transport effect;

[0155] FIG. 2b is an illustration of the voltage pulse shape applied to the electrodes in the matrix over a series of pulses, where the voltage pulse profile is to provide at least a part of the net transport effect;

[0156] FIG. 3a is an illustration of a detailed view of a part of the current pulse shape, showing the preferred form of that part of the pulse in one embodiment of the invention;

[0157] FIG. 3b is an illustration of the same detailed view of a part of the current pulse shape as FIG. 3a, but with too long a duration before the polarity is reversed for that embodiment of the invention;

[0158] FIG. 3c is an illustration of the same detailed view of a part of the current pulse shape as FIG. 3a, but with too short a duration before the polarity is reversed for that embodiment of the invention;

[0159] FIG. 4 is a schematic illustration of the progression from heavy to light to gaseous hydrocarbons as found in oils;

[0160] FIG. 5 is a schematic illustration of a still further embodiment of the invention where processing is provided in a mixing tank;

[0161] FIG. 6 is a schematic illustration of a yet further embodiment of the invention used in an oil sand example;

[0162] FIG. 7 is a schematic illustration of a final further embodiment of the invention used in a transportation based embodiment;

[0163] FIG. 8 illustrates results for the operation of the method on one mixture;

[0164] FIG. 9a illustrates an alternative current pulse shape provided in an alternative embodiment of the invention;

[0165] FIG. 9b illustrates a detail of a part of the current pulse shape of FIG. 9a.

[0166] In FIG. 1, a geological structure 1 is provided which contains a naturally occurring volume of hydrocarbons 5 in a layer of the geological structure 1. The layer in the geological structure 1 contains a mixture 3 that includes solids, liquids and potentially gases, including hydrocarbons 5. Water is a desirable component of the mixture, for instance at the 3 to 10% proportion by volume.

[0167] For example, the hydrocarbons 5 may be the subject of an extraction process 7 including which has provided a production well 9 and potentially an injection well 11. The mixture 3 may be difficult to extract or unsuitable for extraction using existing approaches. For instance, the mixture may contain a high level of heavy hydrocarbons and a relatively low level of light hydrocarbons. This renders the hydrocarbons 5 as a whole viscous and/or well bounded to the geological structure 1 and hence resistant to extraction.

[0168] Previous treatment attempts at the treatment of the hydrocarbons 5 have included the injection of steam or carbon dioxide into the geological structure 1 with a view to using the heat or pressure to reduce the viscosity or form of the hydrocarbons so as to promote movement and hence extraction at a production well. Burning has been used to generate heat and hence crack the oil in-situ. The in-situ treatments can be effective, but these all have limitations in terms of costs and/or effectiveness and they are also time consuming to achieve.

[0169] The present invention provides a series of electrodes 10 arranged along the length 12 and across the width 14 of a matrix 16 which forms a part of the geological structure and which contains the hydrocarbons 5. The electrodes 10 also have a depth 18 within the matrix 16. The electrodes 10 are provided in a regular array in this example, but other configurations can be used.

[0170] Titanium (with a mixed oxide coating or surface, to avoid any insulating layer) and steel represent preferred materials for the electrodes.

[0171] The electrodes are typically 100 m to 500 m apart from each other along the width and the length of the regular array. The electrodes 10 will typically extend down at least 50% of the depth of the matrix 16 being treated and may span the full depth or more. The electrodes typically have a diameter in excess of 5 cm. The electrodes 10 can extend from the surface the whole way down to the depth of the geological structure 1 being treated, or as shown, may only be present within the geological structure 1 itself (or a part therefor). The wiring 20 (only shown for some electrodes) for the electrodes 10 then provides the link to the surface 13.

[0172] The wiring 20 for the electrodes 10 connects them as a first set 22 of electrodes 10, a second set 24 of electrodes 10, a third set 26 of electrodes 10, a fourth set 28 of electrodes 10 and so on. The potential is applied so as to generate a voltage drop between the first set 22 of electrodes 10 and the second set 24. A voltage drop is also generated between the third set 26 and the fourth set 28. This also generates a voltage drop between the second set 24 and third set 26 and between other sets of electrodes 10. The flexibility of the connections provided by the wiring 20 allows for different combinations of electrodes 10 to be connected to form pairs.

[0173] Suitable power sources 30 and power control units 32 are provided at the surface 13 to generate the desired voltage drops and potentials within the system, and hence voltage pulses. The system is driven with a constant voltage supply, typically from 10 V to 2500 V. Typically voltages are used which provide between 0.5 and 5 V/m of separation between the electrodes; hence between 50 V and 500 V with a spacing between electrodes of 100 m.

[0174] The current output level depends upon the circuit resistance. The circuit resistance is affected by the electrical conductivity of the matrix 16, and particularly the fluid contained therein, as well as the number of electrodes provided and the separation between them.

[0175] The profile of the voltages applied and the impact of the applied voltages on the matrix and compounds are described further below.

[0176] During the method, the process conditions are most effective when the pH is within certain bounds. Natural redox reactions and/or reactions caused by the operation of the method can cause a decrease in pH around the anode and/or an increase in pH around the cathode. If the pH becomes too low then electro-osmosis at the anode stops which impairs the operation of the process. If the pH becomes too high then that can have deleterious effects on the process. However, it is believed that the process is still effective at lower pH's than can be tolerated in electro-osmotic based processes where transportation is being sought, as the process is seeking to provide oxidation of organic species.

[0177] To ensure the appropriate pH, the system can include treatment apparatus, not shown, which receives electrode electrolyte from around the electrodes 10. A perforated tube may be provided around each electrode 10 so as to provide a reservoir of electrode electrolyte in contact with the matrix 16. Pumps draw the electrode electrolyte from the reservoirs along pipes to the treatment apparatus. The treatment apparatus includes a pH adjustment stage and potentially other stages for other desirable treatments for the electrode electrolyte. Cleaned pH adjusted electrolyte arises from these stages and can be returned via pipes to the reservoirs. In this way optimum conditions are provided within the reservoirs and for the process as a whole.

[0178] Significantly, the power consumption with the approach of the invention is very low. The voltage pulse profile is illustrated in FIG. 2a. As can be seen, the voltage pulse profile consists of alternate pulses of opposite polarities with time. The voltage pulses are generally square shaped pulses for both polarities and are of equal duration. Hence, the pulses are used to apply the voltages to the matrix 16 but have no net transport effect on the matrix 16 or more particularly the liquid and compounds within it. The transport effect can be provided by the process as described below. However, where the voltage pulse profile does not provide the net transport effect, then other mechanisms may be used, for instance injection of other materials, application of pressure or forms of displacement.

[0179] Where the pulse profile is to provide at least a part of the net transport effect, then a pulse profile of the form illustrated in FIG. 2b may be used. The difference in duration of application of the pulse with one polarity and the duration of application of the pulse with the opposing polarity provides the net transport effect, potentially through electro-osmotic and/or electro-kinetic effects. Generally the pulse operative in the direction of travel will be between twice and five times the duration of the opposing polarity pulse in such cases. A rest with no or little applied voltage may be used between polarity reversals.

[0180] The square voltage pulse profile features a rapid change from one polarity to the other and then back again. Thus regular square shaped pulses are provided rather than a sinusoidal or other gradual form of changing pulse.

[0181] Whilst the voltage pulse profile is generally square shaped, there are important details in the shape of the current pulse which are sought for the optimum operation of the invention. These apply whether the voltage pulse profile is of the FIG. 2a or FIG. 2b type. As shown in FIG. 3a, when the rapid change in polarity is applied, the current profile rises quickly and reaches a maximum level 100. From the maximum level 100 the level gradually declines, for instance along an elliptical curve 102, to a reduced consistent level 104. A short time 106 after the reduced consistent level 104 is reached, the polarity is reversed and the current profile quickly switches to a maximum level, not shown, of the opposing polarity.

[0182] Typical voltage pulse lengths are between 20 and 200 ms. Short rests may be provided to the system between pulses of one polarity and the other. The rests may be 0.5 ms to 50 ms in duration.

[0183] The maximum level 100 is reached as a consequence of the voltage applied causing the matrix, and potentially the liquid, to become charged according to the natural capacitance of the system. This charge is gradually discharged overtime as reflected in the current pulse shape. The maximum level 100 and gradual reduction is indicative of the formation of free radicals within the matrix. These are very beneficial to the overall process, in particular these free radicals are believed to be involved in the oxidation reactions which treat the compounds, such as hydrocarbons. The presence of water, which usually occurs naturally in-situ, is believed to be beneficial in the promotion of the formation of free radicals.

[0184] Beneficially the free radicals are generated exactly where they are needed for the method to provide the desired treatment, namely at the pore surfaces within the matrix. As a consequence, redox reactions are promoted at those locations too.

[0185] The duration of the pulse is beneficial in generating electro-osmotic forces in a first direction, and then when the polarity is reversed, in the opposite direction for any one species present (depending upon its charge). Thus the charged contents of the pore water move quickly back and forward with the polarity changes. This causes freshly formed oxygen and hydroxyl free radical formed in these electrochemical reactions to move back and forth. This also promotes their involvement in the oxidisation of the compounds present. For instance the free radicals can cause hydrocarbon chains to breakdown into lighter fractions and form carbon dioxide and water as by products. The capacitive nature of the matrix and reactions occur at the grain surface where the pollution is.

[0186] The physical nature of the matrix in many cases, small particulate matter with a moderate or low degree of compaction or with loose material within a more fixed body of material, means that the electrophoretic forces generated (which generally oppose the direction of electro-osmotic forces) cause small amounts of movement by the particulate material. The movement is believed to be beneficial in causing reaction product displacement away from the surfaces and/or pH balance.

[0187] The process conditions are optimised to give the desired current pulse profile illustrated in FIG. 3a in one embodiment. The overshoot in the level and the current pulse length which gives the full gradual discharge are desirable.

[0188] FIG. 3b illustrates a situation where the duration before the polarity is reversed is potentially too long. As a consequence, the same maximum level 100 is provided and the same gradual decay to the reduced consistent level 104, but that level is present for a much longer time frame. This reduced consistent level 104 is believed to reduce the efficiency of the process reactions as the free radical generation has stopped or is present at a lower rate during this phase. However, it may assist with the charging for the reversed polarity part and hence with the effects desired from that reverse polarity when it too discharges.

[0189] FIG. 3c illustrates another version of the same current pulse, but with a shorter time period before the polarity is reversed. As a result, the maximum level 100 is present but the reduced consistent level 104 has not been reached by the time the polarity is reversed. As a result it is believe that some of the free radical generating capacity within the system is not exploited and instead energy must be used to reverse the remaining natural part of the capacitance of the system. A detrimental effect on the charging for the reverse polarity part may also occur as a result.

[0190] The power supply conditions needed to provide the current pulse profile of FIG. 3a may vary from matrix to matrix and/or according to the compound to compound situations encountered within different hydrocarbons. However, investigative measurements can be conducted on the particular system to provide the power supply conditions necessary for the desired profile shape and hence process conditions within the matrix.

[0191] The role of the free radicals generated is to promote oxidisation reactions. The conditions in the matrix are optimised in the present invention, thus adding strength of oxidising to any other form of physical and/or chemical treatment.

[0192] Test operations have demonstrated that the process is effective to oxidise a wide variety of organic compounds. Examples include aliphatic organics with C10 to C40, benzene, toluene, ethyl benzene, xylenes, and polycyclic aromatic hydrocarbons amongst other compounds.

[0193] Particularly in the context of hydrocarbons in forms conventionally considered as oils, the process is effective in breaking down the hydrocarbons from heavy forms to lighter forms. This involves increasing the hydrogen to carbon ratio, normally by reducing the length of the average carbon chain within the hydrocarbon; obviously a variety of different lengths are present. The process is particularly effective in acting on asphaltenes, which as can be seen in FIG. 4, are at the heavy end of the spectrum of hydrocarbons encountered in oils. Breakdown of the carbon chains, proceeding from right to left, gives rise to smaller and shorter carbon chains.

[0194] The process is also believed to act on sulphur present, as inorganic species such as hydrogen sulphide, and/or as organic species such as mercaptans and thiophenes. The impact of the oxidation follows a potentially complex route, but leads to less problematic species such as sulphuric acid and sulphates.

[0195] This breakdown to lighter forms is particularly useful in the context of heavy crude oils, such as those extracted in Canada and Venezuela.

[0196] Heavy crude oil is generally considered to be oil with an API gravity of less than 20 (where an API gravity of 10 matches the density of water). An API below 10 leads to the oil sinking in water, and may be classified as extra heavy oils. The classification of oils as light oils varies with geography, but typically are US originating oils with an API of 37 to 42 and are non-US originating oils with an API of 32 to 42 degrees, such as Brent crude at an API 38.06.

[0197] In general, the heavier a crude oil is, then the greater its viscosity, the more resistant it is to flow and the more it binds or adheres to materials it contacts (including the matrix it is found in).

[0198] In general, heavy crude oil also has a higher, undesirable, sulphur content compared with light oil; potentially as high as 4.5%. The process of the invention is believed to have a role in reducing the sulphur content via oxidation and/or conversion to more readily separable forms. In general heavy oil also typically has a higher heavy metal content and that too needs to be reduced. Again the process of the present invention is believed to have a valuable role in the oxidation and/or conversion of those species and may easy separation.

[0199] In general, heavy crude oil needs cracking, refining and purification to make gasoline from it. This increased processing cost makes heavy oils less valuable than light oils; they are less useful and have less demand without the processing and the processing itself is expensive. Heavy oils are also often more expensive to extract and so have higher production costs too. Transportation costs are also often higher due to the viscosity having a negative impact upon pumping and the like. Heavy crude oil also faces environmental problems as the quantity of carbon dioxide released during burning is also much higher.

[0200] The process has many beneficial effects upon the matrix and/or upon the compounds within it. These include:

[0201] Breaking down one or more compounds present to smaller compounds--these may have increased commercial value and/or may be more mobile within the matrix;

[0202] Reducing the level of contaminants present in the water drawn off the system, other through breakdown those compounds or changing their form;

[0203] Changing the surface chemistry of the matrix or species which form the matrix--either in terms of the physical chemistry of the matrix itself or in terms of the ions or other species present at the surface or the charge level of the surface--these can promote better release of the hydrocarbons from the matrix.

[0204] In the FIG. 1 illustration, the process is shown providing in-situ processing of the hydrocarbon within a geological structure 1. The process can be used to treat a wide variety of structures or situations where hydrocarbons are present and would benefit from a degree of oxidation. The matrices can include soil, groundwater bearing matrices, aquifers or other forms of geological structure containing the hydrocarbons to those described, including oil sand situations. Many or even all of these situations include naturally occurring water within the matrices to be treated. The addition of water, in liquid, gaseous or steam form, before or during the proposed processing is also a possibility.

[0205] FIG. 5 illustrates a further embodiment of the invention in which the similar principles and elements of the process are deployed in a quite different situation again. In this case, a tank 300 is provided which contains a volume of hydrocarbons which are too heavy or too sour. Rather than blend this oil with a lighter oil (potentially imported to the country or transported a long way within the country) to produce a blended oil with a higher API, the process seeks to treat the heavy oil. Blending is effective to a degree, but requires the mixing of large volumes of expensive light oil with the heavy oil to reach a commercial product. This increases the costs of reaching that commercial product and involves material amounts of financial capital to secure and put through the process the lighter oil. Many countries which have the heavy oil do not have their own sources of light oils. If the hydrocarbon to be treated is devoid of water or low in water, then water may be added before and/or during processing. The water may be added as a liquid, gas or steam form.

[0206] In FIG. 5, the electrodes 302 are provided near the walls 304 of the tank 300. A smaller number of electrodes 306 are placed towards the centre of the tank 300. Again, voltage pulses, current pulses and the other features described for the invention are provided so as to provide the oxidation effects and breakdown the oil in the tank 300. In an alternative form, not shown, the walls of the tank act as one of the electrodes or as a series of electrodes. The tank 300 is provided with an outlet 308 which leads to a pump and return inlet 310 so as to circulate oil and cause the oil in the tank to mix and have homogenous properties. The residence time within the tank 300 is controlled so as to give the desired form for the oil produced from it. This light oil can be sold as is, and/or can be used in a subsequent blending processes, for instance to blend with volumes of untreated heavy oil from the same or different extraction locations. The tank 300 can be a specifically constructed processing tank or could be a tank normally used for storage purposes. The technique is suitable for use in relatively large tanks, such as tanks which are 30 m of more in diameter. Suitable provision may be provided for collecting and dealing with any off gassing arising from the processing.

[0207] As well as the vertically arranged electrodes discussed above, further electrodes 320 are provided in a similar regular array across the width and length of the tank 300. In this case a series of horizontally extending electrodes 320 are provided. These are connected to the same wiring system. They can be used to form pairs of electrodes amongst themselves and/or be combined with vertically provided electrodes 302. These electrodes are provided at a depth d below the surface of the volume of material. These electrodes can be provided in a fixed position within the tank 300 or can be raised and lowered within the tank 300 as desired. They are used in a similar manner to the vertical electrode operation described above. The combination of electrode arrangements is used to increase the volume of material being treated or in closer proximity to an electrode.

[0208] Tanks of the type illustrated above could be used at the extraction site, at intermediate storage locations receiving oil from multiple extraction sites, at initial blending installations or at refineries where other processing is also provided.

[0209] As well as the heavy oils discussed above, the embodiment illustrated in FIG. 6 shows the invention in use at an extraction site which is concerned with oil sands (including tar sands and bituminous sands). Such deposits are to be found in Canada, Russia and Kazakhstan. They generally consists of loose sand or partially consolidated sandstone which contains viscous hydrocarbons (often classified as bitumen) as well as the matrix of sand, clay and water. In this embodiment, the array of electrodes 400 are driven into the ground 402 over the area 404 to be treated and the same type of general processing using the voltage pulse profiles and current pulse profiles is provided.

[0210] The viscosity of the hydrocarbons may be too high to achieve any transport at the outset and so no net transport effect may be provided to begin with. With time, the processing breaks the hydrocarbons down and reduces the viscosity. In a further phase, a net transport effect may be provided, using the voltage pulse profiles of a different form and/or using other transport mechanisms, such as "cold heavy oil production with sand" or "cyclic steam stimulation" or "steam assisted gravity drainage" or "vapour extraction" or "toe to heel air injection" or other such techniques for extraction assistance which are known in the art.

[0211] FIG. 7 shows a further situation in which the treatment process is provided. In this case, the treatment is provided during transportation. A form of on-line blending is provided. However, rather than add to the pipe 500 providing the transportation of the oil 502 different types of oil and allowing those to mix as they pass along the pipe 500, this embodiment of the invention applies the invention's processing during transportation. Thus, the pipeline 500 is provided at periodic intervals with a series of electrodes 504 inside the pipe and in contact with the oil 502. The processing is achieved in the same manner. A variety of electrodes 504 can be used including elongate electrodes of the type illustrated above, mesh or grid style electrodes extending across the cross-section of the pipe 500 or others. The aim is to apply the conditions to the oil as it passes and give a reduction in density and in viscosity, an increase in value and easier handling, pumping and transportation of the oil 502. Again, if the hydrocarbon to be treated is devoid of water or low in water, then water may be added before and/or during processing. The water may be added as a liquid, gas or steam form.

[0212] FIG. 8 illustrates the variation observed in a number of characteristics of a mixture when treated according to the method of the present invention over an extended time (in hours) on the x axis.

[0213] At the start of the method, the heavier hydrocarbons (black line) are present at a concentration of over 200,000 mg/kg of the mixture. As the method is performed, the method serves to breakdown the heavier hydrocarbons to lighter forms and so the concentration declines. The method reduces the concentration to around 1/4 of its original value.

[0214] At the start of the method, the lighter hydrocarbons (red line) formed a relatively small part of the mixture and hence the concentration is low at less than 20,000 mg/kg of mixture. As the process converts the heavier hydrocarbons to lighter hydrocarbons, then this concentration increases. The method increases the concentration to around 10 times its original value.

[0215] FIG. 9a illustrates a preferred current pulse profile for some methods. Each cycle includes a positive polarity triggered current part 500 and a negative polarity triggered reverse current part 502. The current part 500 is formed of a first section 504, second section 506, fourth section 508 and third section 510 which occur in that sequence. Matching but reversed sections are provided for reverse current part 502, such that it has a first reversed part 512, second reversed part 514, fourth reversed part 516 and third reversed part 518. The next positive current part would then be present as the cycle is repeated over and over by the application of an appropriate voltage pulse profile (not shown).

[0216] FIG. 9b shows the peak part of the pulse in more detail. The first section 504 shows the current increasing quickly as it is encouraged by the change in the voltage pulse profile. As a result the voltage induced current and the current caused by the discharge of the capacitance built up during the previous reversed current part (not shown) occurs. These two current elements rapidly cause the peak current 520 to be reached.

[0217] As the capacitance of the system is discharged, then the current element from that diminishes in a curved decay through the second section 506. The voltage pulse still maintains a current though. Once the capacitance has effectively discharged, then the second section 506 transitions into the fourth section 506. The steady current occurs through the fourth section 506 before a further change in the voltage pulse (not shown) causes the rapid reduction of the current to zero during the third section 508, shown in FIG. 9a. A similar or matching peak occurs for the reverse polarity part and so on through the cycles.

[0218] The voltage pulse profile can be used to control the shape and timing of all of the sections of the current pulse profile.

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