WO2015176779A1

WO2015176779A1 - Oil and water separation

Info

Publication number: WO2015176779A1
Application number: PCT/EP2014/060743
Authority: WO
Inventors: Kjetil Fjalestad; Jon Arild Svendsen; Ulf Kristian SANDVIK
Original assignee: Statoil Petroleum As
Priority date: 2014-05-23
Filing date: 2014-05-23
Publication date: 2015-11-26

Abstract

The invention relates to a fluid flow controller for use in an oil extraction system. The fluid flow controller comprises a positive electrode (10), a negative electrode (22) and a porous material (16) between the positive and negative electrodes. When an electric field is applied between the positive and negative electrodes flow of water through the porous material is controlled. Thus the water and the oil are separated.

Description

Oil and Water Separation

Technical field The invention relates to the field of oil reservoirs and wells for extracting oil from such reservoirs. It relates to the field of oil transport in pipes and oil processing plants.

Background Figure 1 a is a schematic illustration showing some of the features of a typical oil production well. A plurality of production wells 10 extend down through the ground from the well head 18 on the surface. The production well 10 extends into a reservoir or formation containing an oil layer 12 from which oil is extracted from a porous reservoir through the walls of the production well along the well to the well head. The formation also typically contains layers of gas 14 and water 16. Figure 1 b shows the water saturation levels in the various layers. As shown, there is initially little water within the oil layer. However, over time as oil is drawn into the well, water will enter the oil layer and replace the oil which has been extracted. Once the tip of the water front/cone/finger reaches the well, water will enter the well with the oil.

It would be desirable to produce oil from formations leaving the water behind. If the water content of the produced oil could be reduced (or even totally prevented), this would reduce the need for fluid processing, e.g. separation at the well head. It would also be beneficial to separate water and oil efficiently at any desired location, e.g. inside the well pipe, transportation pipes, or at top side processing equipment.

Summary of the invention

According to a first aspect of the invention, there is provided a fluid flow controller for use on or inside a well pipe within an oil extraction system extracting oil from a reservoir, on a transportation pipe or on other process equipment within the oil extraction system or in similar systems. It thus relates to the field of oil transport in pipes and oil processing plants. The fluid flow controller comprises a positive electrode, a negative electrode and a porous material between the positive and negative electrodes. In use, a voltage is applied to the positive and negative electrodes to generate an electric field between the electrodes to control the flow of fluid within the porous material.

Within a reservoir from which oil is being extracted, there is typically both oil and water. Water is an electrolyte but oil is not. Hence, applying an electric field E within a system containing both oil and water will cause the water but not the oil to move using electro- osmotic flow. The use of the fluid flow controller allows the flow to be controlled at a micro-level by providing fluid flow controllers which may act as barriers, valves or channels along parts of the water and/or oil pipes (e.g. the injection and/or production wells or transportation pipes). Alternatively, as explained in more detail below, the flow can be controlled at a macro-level, in other words, throughout the entire reservoir with the rock comprising the reservoir forming the porous material between the electrodes.

The strength of the applied voltage may be adjustable to control the electric field between the electrodes and hence to control the fluid flow. For example, the electric field may be calculated from:

U

^E = h where h is the distance between the electrodes and U is the applied voltage. The distance between the electrodes is fixed and thus increasing the voltage will increase the electric field and vice versa. Accordingly, if the desired electric field is known, the voltage to be applied can be determined. The applied voltage may be calculated within the controller or in a separate control system to which the controller is connected. In the latter case, the controller may be part of a system which comprises a plurality of the fluid flow controllers and a control system for controlling each controller.

Water flow is generally proportional to the electric field, E, over the length, h, filled with water. If other fluids are entering the porous material, that will affect the electric field over the water zone. In addition the total electric resistance, R, will change, and thus the electric current, I. Since the electric current can be determined from Ohm's law (U = R^*l), it can be derived that the water flow in the porous material depends on the electric current. The current within the porous material may be calculated based on the voltage to be applied and knowledge of the properties of the porous material and the fluids. Hence, the applied voltage will determine the water flow through the porous material. Accordingly, the applied voltage may be used to control the water flow by calculating the expected water flow from the applied voltage using the fact that the water flow is proportional to the current within the porous material. The electric current within the porous material may be measured and monitored. Thus, if the current falls short of the expected or calculated current value, this is indicative of a problem within the controller, e.g. clogging in the porous material. Thus, the applied voltage may be altered, e.g. reversed to cause the water flow to be reversed and clean the porous material, based on the measured current. The calculation of the current and/or the applied voltage based on current measurements or calculations may be done within the controller itself or in a separate control system to which the controller is connected.

The properties and design of the porous material may also be selected and/or adjusted to suit the purpose of the fluid flow controller. For example, the porous material may be a nano-material, e.g. graphene. An important property of nano materials is that the surface area to volume ratio is extremely large and thus the properties of the material can be maintained even when the material is subject to a large pressure drop (e.g. as oil passes through into the well). Graphene has good mechanical, electrical and thermal properties which is useful to combine the electro-osmotic effect with the nano material.

Whilst oil is not an electrolyte, controlling the water flow also controls the flow of oil through the fluid flow controller, e.g. if water is prevented from flowing through the fluid flow controller, oil may flow through instead. The properties and design of the porous material may be selected to optimise oil flow through the fluid flow controller. As an example of the properties and design, the porous material may be a hydrophobic material, e.g. hydrophobic sand, to prevent water flow through the fluid flow controller. It will be appreciated that a hydrophobic material may be used on its own without the electro-osmotic effect of applying an electric field. Alternatively, the properties and design of the porous material may be selected to optimise water flow through the fluid flow controller. For example, the porous material may be an oil-phobic material. Again, it will be appreciated that an oil-phobic material may be used on its own without the electro-osmotic effect of applying an electric field. Thus, according to another aspect of the invention, there is provided a flow controller for use on an oil well, transportation pipe and other process equipment, the fluid flow controller comprising a porous material which is an oilphobic material. The fluid flow controller may comprise a pressure mechanism for controlling the fluid pressure on either side of the porous material. For example, the porous material may be configured to separate a first chamber from a second chamber wherein in use there is predominantly water in the first chamber and a mixture of water and oil in the second chamber. In this arrangement, the pressure mechanism is configured to ensure that the pressure in the first chamber is greater that the pressure in the second chamber to prevent oil from the second chamber being drawn into the first chamber by pressure differences. This is particularly important where no electric field is used to control the fluid flow through the porous material.

As set out above, the fluid flow controller is suitable for use on a well within an oil extraction system. Typically, an oil extraction system comprises one or both of a production well for extracting oil from the reservoir and an injection well for injecting fluid into the reservoir. Thus, according to another aspect of the invention, there is provided a production well for extracting oil from the reservoir, the production well comprising at least one fluid flow controller as described above. Similarly, according to another aspect of the invention, there is provided an injection well for injecting fluid into the reservoir, the injection well comprising at least one fluid flow controller as described above. The fluid controller is also suitable for other transportation pipe. Thus according to another aspect of the invention, there is provided a transportation pipe, the transportation pipe comprising at least one fluid flow controller as described above. By comprising, it is meant that the fluid flow controller may be within the well or pipe or may be formed integrally therewith. It will be appreciated that the fluid flow controller, the injection well, the transportation pipe and/or the production well may be separately or integrally formed.

A fluid flow controller on the production well may be designed so that the application of the electric field assists in minimising or reducing water flow and maximising or increasing oil flow into the production well. A fluid flow controller on the production well may also be designed so that the application of the electric field assists in removing water from the production well through the fluid flow controller. By contrast, a fluid flow controller on the injection well may be designed so that the application of the electric field draws fluid (e.g. water) into the injection well and/or ejects fluid (e.g. water or steam) from the injection well at a different location. The fluid flow controller may have a generally annular shape. This is particularly useful where the injection and/or production well comprise at least one fluid flow controller. An annular fluid flow controller may sit around the outer surface of at least part of the wall of the injection and/or production well or form part of the wall.

Water flows from the positive electrode to the negative electrode. The positive electrode may be on an inner surface of the fluid flow controller and the negative electrode may be on an outer surface of the fluid flow controller. When such a fluid flow controller is used on an injection well, the application of an electric field may draw water from within the injection well to be injected into the reservoir through the fluid flow controller. When such a fluid flow controller is used on a production well, the application of an electric field may prevent or reduce water flow into the production well. Thus, in this case, the fluid flow controller acts as a water barrier

Alternatively, the fluid flow controller may have the positive electrode on an outer surface and the negative electrode on an inner surface. When such a fluid flow controller is used on an injection well, the application of an electric field may draw water into the injection well.

In any of the arrangements described above or below, the polarity of the electrodes may be interchanged, i.e. the positive electrode becomes the negative electrode and vice versa. One use is to avoid clogging pores in the porous membrane. The polarity may be changed at regular or irregular intervals which may span nano seconds or days depending on what is most effective in a particular situation. Such interchanging of polarity may be termed pulsing and may be beneficial for transport and chemical reactions.

The injection well and/or the production well may comprise a plurality of fluid flow controllers as described above. The fluid flow controllers may be spaced apart along at least part, possible the whole, length of the injection well and/or the production well. There may be a combination of different fluid flow controllers on the well, for example some which allow water to be drawn into the injection well from the production well and some which inject water. This is an efficient arrangement which reduces the need for water to be drawn from an alternative source and hence pumped into the reservoir. The electric field applied to each fluid flow controller may be independently adjustable giving greater control.

Furthermore, by measuring the electric current for each electrode pair along the pipe, the water volume flow may be calculated. The water volume flow is a function of the measured electric current and the parameters of the device itself such as pulse intervals, pressure difference across the membrane, applied voltage across the membrane, pore diameter of the membrane, thickness of membrane, type of material (electrodes and membrane), porosity of the membrane and physical properties of the fluids. If the measured electric current is reduced it indicates there may be clogging within the device. To prevent clogging pulsing can be used or the applied voltage can be changed. This can be done at regular intervals or if the electric current has reached a limit. Thus the water flow volume may be used for minimising the power consumption and clogging (e.g. using pulsing as described above).

As an alternative (or in addition) to using a plurality of fluid flow controllers, each fluid flow controller may be divided into a plurality of sections each of which can be controlled separately. For an annular fluid flow controller, the sections may be radial sections. Alternatively, in other arrangements the sections may be axial. This provides additional flexibility and control in the system. A current sensor may be used for measuring the current within the porous material of each fluid flow controller section. The voltage applied to each of the positive and negative electrodes in each section may be determined based on the measured current. The injection well and/or production well form part of an oil extraction system. Thus according to another aspect of the invention, there is provided an oil extraction system for extracting oil from a reservoir, the oil extraction system comprising: an injection well for injecting fluid into the reservoir; a production well for extracting oil from the reservoir, and at least one fluid flow controller as described above. Alternatively, there is provided an oil extraction system comprising: an injection well as described above; and a production well as described above.

The injection well may be positioned within the production well along at least part of its length. In this arrangement, when an electric field is applied water may be drawn through the fluid flow controller from the production well into the injection well. This may be achieved, for example by a fluid flow controller having the positive electrode on an inner surface and the negative electrode on an outer surface wherein water is drawn in the opposite direction to the applied electric field. It may be possible, because of fluid levels within the production well for the fluid flow controller to comprise porous material in its lower section only and be non-porous elsewhere. This may reduce the use of an expensive porous material. In this arrangement, the injection well may be replaced by a transportation pipe to remove water from the system where it is not needed to inject the water into the system. The injection well and the production well may be adjacent one another along at least part of their length. In this arrangement, at least one fluid flow controller may be used to connect the injection well and the production well where the wells are adjacent one another. At least one fluid flow controller forms a channel between the production well and the injection well whereby when an electric field is applied to the at least one fluid flow controller, water is drawn through the channel from the production well into the injection well. In this arrangement, the porous material may be housed within a housing to define the channel between the two wells, e.g. a channel having a generally rectangular cross-section. As above, the injection well may be replaced by a transportation pipe to remove water from the system where it is not needed to inject the water into the system.

A combined production and injection well may also be used. The combined well may comprise a production chamber which forms the production well and an injection chamber which forms the injection well, wherein the fluid flow controller extends along the length of the combined well to separate the chambers. The positive electrode may be adjacent the production chamber and the negative electrode adjacent the injection chamber so that when an electric field is applied between the positive and negative electrodes, water flows through the fluid flow controller from the production chamber into the injection chamber. Again this means that water need not be pumped from a separate source and also improves the quality of the fluid from the production well. In this arrangement, the fluid flow controller is acting as a wall or barrier between the two chambers. The fluid flow controller may be planar or non-planar.

The fluid flow controller may be flexible. Such a flexible fluid flow controller may locally alter the volume of each of the production and/or injection chambers depending on the local pressure difference between the fluids at various positions. This property can be used for advanced volume and flow control in both radial and axial directions. It is favourable with a large mass transfer area for water on the membrane surface. Furthermore, it can create a flow regime such as a swirl that moves water towards the membrane. The pressure in the injection chamber (i.e. on the water side) is preferably higher than the pressure in the production chamber (i.e. on the oil side) otherwise oil may be forced through the fluid flow controller. However, if the pressure difference is too great, the electric field will need to be very strong to overcome the pressure difference. Accordingly, the pressure difference is preferably minimised to minimise power consumption. The pressure difference may be measured and an outlet valve may be provided on one or both sides of the fluid flow controller or provided within the injection chamber to release fluid therefrom. The outlet valve may be activated when the pressure difference is too great. The activation may be automatically controlled. As above, the injection well may be replaced by a transportation pipe to remove water from the system where it is not needed to inject the water into the system.

The oil extraction system may comprise a control system for controlling each fluid flow controller within the oil extraction system. The control system may be used to determine the voltage to be applied to each fluid flow controller. The voltage may be determined based on current and/or pressure measurements which are received by the control system.

In the examples above, the porous material is within the fluid flow controller and may thus be controlled as desired. However, the electro-osmotic effect may also be used on a macro-scale in which case the porous material may be the rock within the reservoir itself. For macro-control, a pair of electrodes is positioned with the porous material between them. However, in this case, the negative electrode is at a significant distance, i.e. a distance much greater than the width of a well, from the positive electrode. Thus according to another aspect of the invention, there is provided an oil extraction system for extracting oil from a reservoir at least one pair of electrodes in the reservoir, wherein the or each pair of electrodes comprises a positive electrode and a negative electrode which are set a distance H apart within the reservoir, means for applying an electric field to the or each pair of electrodes and a controller to control the applied electric field. This embodiment may be used independently or in conjunction with the micro-embodiments described above. In the macro-embodiment, the or each pair of electrodes may be either side of an interface between a layer of oil and a layer of water in the reservoir; whereby a distance h between the interface and one of the electrodes is controllable. The flow of fluid may be controlled to control the interface between layers of oil and water in the reservoir. The system may thus comprise a controller which is configured to calculate a distance between the interface and one electrode in the pair of electrodes; determine whether said calculated distance is within an expected range and output an adjustment to the applied electric field when it is determined that said calculated distance falls outside said expected range. The system may comprise at least one current sensor for measuring the current within the reservoir or the current may be measured at the power supply. The system may comprise at least one resistivity sensor for measuring the resistivity of the rock, oil and/or water within the reservoir. The distance h between the interface and the electrode may be calculated from the voltage and current of the applied electric field together with the resistivity of oil, water and rock within the reservoir.

The calculating, determining and adjusting steps may be repeated at periodic intervals. In this way, the correct interface level may be maintained over time. The expected range may also be altered, e.g. by a user or automatically by the system. When an alteration is input into the system, the calculating, determining and adjusting steps may be repeated again. In this way, any changes to the electric field which are necessitated by the change to the expected range may be calculated. The expected range may be changed so that the direction of the electric field is reversed at the adjusting step. In this way, water may be drawn towards the negative electrode to assist with oil extraction, i.e. to force oil into the production well.

There may be a plurality of pairs of electrodes, which for example are spread throughout the reservoir. A plurality of separate electric fields may be applied using separate pairs of electrodes and the calculating, determining and adjusting steps may be performed separately for each pair of electrodes. Each pair of electrodes may have an associated expected range which is separately adjustable. This may enable a water sweep through the reservoir to assist in oil recovery. Both macro and micro control of a fluid using electro-osmotic effect is described above. Thus, in a very general sense, there is provided, according to an aspect of the invention, an oil extraction system for extracting oil from a reservoir, the system comprising at least one pair of electrodes in the reservoir with a porous material between the electrodes, wherein the pair of electrodes comprises a positive electrode and a negative electrode and means for applying an electric field to the electrodes to control fluid flow within the porous material whereby fluid flow within the reservoir is controlled. For macro control, the porous material may be the reservoir material itself. For micro control, the porous material may be designed for optimum use. The features of the various aspects of the invention described above may be used in this general aspect.

Brief description of the drawings These and other aspects of the invention will now be further described, by way of example only, with reference to the accompanying figures in which:

Figure 1 a is a schematic illustration of a standard well head with a plurality of production wells extending into formations containing oil;

Figure 1 b is a schematic cross-section of a formation from which oil is being extracted in a conventional manner;

Figure 2a is a schematic cross-section of a formation from which oil is being extracted using an electro-osmotic effect;

Figure 2b is a flowchart showing how the voltage to be applied is determined;

Figure 2c is a schematic block diagram of the system for implementing the steps of the flowchart of Figure 2b;

Figure 2d is a schematic close-up of a section of a formation from which oil is being extracted using an electro-osmotic effect; Figures 3a to 3c show the formation of Figure 2a with an alternative arrangement for extracting oil using electro-osmotic effect;

Figure 4 is a schematic illustration of a steam assisted gravity drilling (SAGD) arrangement for extracting oil using an electro-osmotic effect;

Figures 5a and 5b are cross-sections across a production well such as that used in Figure 2a; Figure 5c is a cross-section along the length of the production well of Figure 5a;

Figure 6 is a cross-section through adjacent production and injection wells according to another aspect of the present invention; Figure 7a is a cross-section through a pair of production and injection wells according to another aspect of the present invention;

Figure 7b is a cross-section through an injection well which may be used in the arrangement of Figure 7a;

Figure 7c is a cross-section through a pair of production and injection wells according to another aspect of the present invention; and

Figure 8 is a schematic cross-section of the pair of wells of Figure 7c showing pressure control.

Detailed description of the drawings

Figure 2a shows the formation of Figure 1 a in which there are two wells; a first well 10 which is the production well and a second well 22. Each of the wells comprises an electrode or is itself an electrode to which a voltage is applied. The second well 22 may be an injection well, e.g. to inject water back into the formation to replace the withdrawn oil so that pressure levels within the formation are maintained. Alternatively, the second well may just be a dummy well for the insertion of an electrode at a suitable location. It may also be possible to place the electrode on the sea bed without needing a separate well.

Water is an electrolyte but oil is not. Hence, applying an electric field E within a formation containing both oil and water will cause the water but not the oil to move using electro-osmotic flow. The direction of the flow is in the direction of the applied electric field, namely from the positive electrode (anode) to the negative electrode (cathode). Accordingly, as shown in Figure 2a, the production well 10 comprises a positive electrode and the second well 22 comprises the negative electrode so that water flows away from the production well.

This water flow is schematically illustrated in Figure 2d which shows a production well 10 positioned at the top of the oil layer 12. The production well 10 has an electric field applied to it from the generator 24 to be a positive electrode. There are two electrodes 22 in the water layer 16 both of which are connected to the generator 24 so that they are negative electrodes. These electrodes 22 may be within second wells or may be positioned without a well if possible. The direction of the water flow is indicated by arrows A. In both the arrangements of Figures 2a and 2d, the positive and negative electrodes are set at a height H from one another. One consequence of applying the electric field is that the height of the water cone shown in Figure 1 a is reduced as shown in Figure 2a. Water and oil do not mix and there is thus an interface or surface at which the two layers meet. The distance from the positive electrode to the water-oil interface is indicated as height h. The electric field E may be applied to maximise h so that the water-oil interface is significantly below the production well and thus water cannot flow into the production well.

The first step is to determine the resistivity of the formation within which the oil is located (S100). The resistivity of the rock may be measured before the production well is inserted or may be measured when the oil is being produced. The resistivity may be measured using known methods, e.g. for core samples taken when the well was drilled. The resistivity of the oil and water are next measured (S102). It will be appreciated that these can be measured together with the resistivity of the formation. However, the resistivity of the oil and water are more likely to be changing with time and thus may need to be more frequently measured. These may be measured from the water and oil which is drawn out of the well, i.e. at the well head or at the power supply, or may be measured by sensors located within the well. The repetition of the measurement can be at regular intervals which may be between 10 minutes and an hour apart.

The next stage is to apply a known voltage U (S104) to generate the electro-osmotic flow (according to known principles). The current I is then measured (S106). The simplest method may be to measure the voltage and current at the power supply. However, it is possible that the current within the electric field may be measured using sensors located within the formation. The height h, i.e. the distance from the well containing the positive electrode to the oil-water interface, is then determined using the equation above (S108). The determined height is compared with a threshold value to determine whether or not the determined height is within the acceptable range for production If the height is acceptable, the system loops back to measuring the current I and recalculating the height to make sure that the production continues to remain within the acceptable parameters. The repetition of the measurement can be at regular intervals which may be between 10 minutes and an hour apart. The measurements can be timed to take place at the same time as the resistivity measurements above.

If the height h is not acceptable, the system determines a correction to the applied voltage U, e.g. increases the voltage if the height is too low or reduces the applied voltage if the height is too great (S1 12). The system then loops back to apply the corrected voltage (S104) and to repeat the measuring and determining steps to make sure that the applied correction has had the desired effect.

Figure 2c is a schematic block diagram of the components of the system. The system comprises a controller 100 which comprises a processor 106 (e.g. a microprocessor), memory 108 and program code 1 10. The functionality of the controller 100 is shown within a single device (e.g. a server) but as is well known in the art may be distributed across multiple devices. The processor and memory of the controller are standard well known component and are not described in detail. The controller is a hardware device which is programmed and controlled by program code 1 10 in a standard known manner. The controller 100 receives data from a current sensor 102 and one or more resistivity sensors 104. The controller may use the data to determine whether or not any changes to the applied voltage U are to be made as described above. If a change is to be made, the controller may directly notify the generator 1 12 which applies a different voltage to the electrodes 1 14 within the formation. In this way, automatic control of the production well is achieved. However, the controller 100 may also output suggested changes to a display of a user computer 1 16. The user may be to input changes to the generator 1 12 or may send the changes via the controller 100. The user computer 1 16 also has a user interface by which the user can input control information to the controller 100 or the generator 1 12.

Figure 3a shows a schematic illustration in which the production well 10 extends along the upper surface of the formation and the injection well 22 along the lower surface of the formation. A plurality of positive and negative electrodes 30,32 are distributed along each well. The electrodes may be equidistantly distributed along each well as shown or may be distributed according to another pattern (e.g. more closely at the far end of the wells). Each of the electrodes is preferably separately driven so that a different electric field can be achieved between each pair of electrodes. As shown in Figure 3b, there are four water cones 20 between four different pairs of electrodes. There is also an area 34 of the formation from which oil production is slowing down. Accordingly, it is desired to force water into this area to accelerate the drawing of oil from this area. The height of the water cone, and thus the height of the water-oil interface, may be controlled as described above. By decreasing the electric field, the height of the water cone may be increased. In more extreme cases, it may be necessary to reverse the direction of the electric field between the electrodes either side of area 34, to attract water towards the production well and further increase the height of the water cone 20 in this area. Thus, as shown there are more (seven) water cones shown in Figure 3c. Reversing the electric field, changes the water flow direction and the additional flow of water forces more oil into the production well to increase the drainage and oil recovery. Accordingly, another use of the electro- osmotic flow is to improve the water sweep within the formation to increase the oil recovery from the oil reservoir within the formation. Figure 4 shows another use of the electro-osmotic flow. Figure 4 shows a reservoir 210 of oil sand beneath other layers of rock, soil etc. A known method of extracting the bitumen from the reservoir is to drill two well lines 212, 214 into the reservoir forming a wellpair. The first well line 212 is for inputting steam into the reservoir to heat the bitumen. The arrows along the well line indicate the direction of steam flow. The second well line 214 is for extracting the bitumen from the reservoir. As shown, the two well lines are not connected to each other and are spaced apart, perhaps generally parallel to one another into the reservoir. Initially, the steam injected into the reservoir creates a small steam chamber. The steam expands in both the longitudinal and axial direction as indicated by arrows A and flows to the interface between the steam chamber and the reservoir. The steam expansion gradually expands the steam chamber 218. The steam heats the bitumen which flows under gravity to the lower portion of the steam chamber as indicated by arrows B. The bitumen (and any other condensate) is drawn off through the second well line using a pump. The arrows along the well line indicate the direction of output fluid flow. Uniform steam chamber development is critical to ensure a productive well.

The well lines 212,214 comprise electrodes as described above and an electric field is applied to control the electro-osmotic flow of the steam which is input into the reservoir. The applied electric field will also generate heat in the reservoir which will aid in the recovery of the bitumen. Using the electro-osmotic effect with steam is the same as with water although the efficiency may be reduced because the molecules are further apart in steam when compared with water.

In the above examples, electro-osmotic flow is used on a large scale to control the water flow within the entire reservoir/formation. Figures 5a to 5c show how electro- osmotic flow can be used at a smaller scale to help prevent water flowing into the production well. This can be done independently of or in conjunction with the large scale described above.

Figures 5a and 5b are schematic cross-sections across a production well. A fluid flow controller which in this arrangement acts as a barrier 40 as explained in more detail below surrounds at least part of the well. The barrier 40 comprises an outer layer 42 and an inner layer 44 and is generally annular in cross-section. The inner layer 44 is adjacent the outer wall of the production well. As shown in Figure 5a, the barrier 40 is divided into four sections 41 a, 41 b, 41 c and 41 d which may be independently controllable. As shown more clearly in Figure 5b, the inner layer 44 forms a positive electrode and the outer layer 42 forms a negative electrode so that an electric field illustrated by the arrows is generated within the layer. The electric field is radially directed from the inner layer towards the outer layer. The strength of the electric field may be adjusted as required by the controller 100 of Figure 2c and may be same through the entire barrier or different in the different sections 41 a-d. As explained above, water but not oil is affected by an electric field. Accordingly, the application of the electric field will prevent (or at least reduce) water flow through the barrier into the production well whilst still allowing oil to flow into the well. It will also be appreciated that by reversing the electric field, any water within the well will be forced out through the barrier. Thus the barrier could also be applied to an injection well to promote the flow of water from the injection well into the reservoir.

A porous medium is contained between the inner and outer layers 42, 44. The porosity of the medium may also be selected to optimise transmission of the oil through the barrier. The porosity of the medium may be selected to prevent clogging of the oil or other unwanted effects. Other properties such as tortuosity may also be optimised. The porous medium may also be a hydrophobic material to prevent water flowing through the barrier into the production well. Furthermore, a hydrophobic material will also reduce water flow through the barrier parallel to the well. It will be appreciated that a hydrophobic material may be used on its own without the electro-osmotic effect but that the combination of the two effects is likely to produce better results.

The hydrophobic material may for example be hydrophobic sand which can be applied as gravel pack around the outer wall of the production well. The hydrophobic material may also be a conductive material which enhances the electro-osmotic effect. The material of the barrier may be a porous nano material such as those which may be designed to be hydrophobic or hydrophilic. An important property of nano materials is that the surface area to volume ratio is extremely large and thus the properties of the material can be maintained even when the material is subject to a large pressure drop (e.g. as oil passes through into the well). An example of a suitable nano material is graphene which has good mechanical, electrical and thermal properties which is useful to combine the electro-osmotic effect with the nano material.

The barrier can be used along the whole or parts of the well. Figure 5c is a schematic cross-section along the length of a production well and shows that the barrier 40 is formed in separate, discrete sections rather than along the full length of the production well. As shown, each section of the barrier is equally spaced from the next section but it will be appreciated that the placement of each section can be varied as necessary, e.g. to have more barriers in parts of the reservoir having more water or where more water needs to be injected. The outer wall of the well may be non-porous to both oil and water in the regions between the barriers and thus as indicated by the arrows, flow into the well may only occur in the barrier regions which in effect form channels into (or out of) the well. If the barrier is using electro-osmotic effect, the strength of the electric field applied to each region of the barrier may be independently adjustable to control the water flow in each region. This may be particularly useful where the barrier is used on an injection well because it enables the injection of water into localised areas within the reservoir. The electric field E may be calculated from:

U

^E = h Where h is the distance between the electrodes and U is the voltage. Thus, the voltage U may be adjusted to give a desired electric field E. The direction as well as the strength may be controlled (e.g. by the controller of Figure 2c). The direction of the electric field may be interchanged, e.g. pulsed. Figure 6 shows another example of how electro-osmotic effect can be used to promote water flow through a fluid flow controller which in this arrangement acts as a channel whose porosity is controllable. As shown in Figure 2a, there may be two wells within a reservoir (or formation). One well is the production well for drawing oil from the reservoir and the second well may be an injection well through which water (or steam) is injected into the reservoir, for example to maintain the pressure within the reservoir. In Figure 2a, the two wells are shown spaced apart, at least within the reservoir itself. Figure 6 shows an alternative arrangement in which the two wells 310, 312 are adjacent one another; at least along part of their length. In Figure 6, the production well 310 is located above the injection well 312, although clearly the positions could be reversed. A channel 314 is connected between the production and injection wells and allows fluid to flow between the two wells 310,312. The production well 310 typically contains a mix of oil (and possibly gas) with water and the injection well 312 contains water. As shown in Figure 6, two electrodes are placed in the channel, one adjacent each well. A positive electrode is placed adjacent the production well 310 and a negative electrode adjacent the injection well 312. An electric field is applied to the channel 314 to promote the flow of water from the production well 310 into the injection well 312, i.e. from the anode to the cathode. Oil, which is not an electrolyte, is unaffected by the electric field and remains within the well. In this way, the electro-osmotic effect is creating a pump so that waste water is removed from the production well into the injection well where it can be recirculated into the reservoir as needed. The channel 314 comprises a porous material, which may be as described in relation to Figures 5a to 5c. Thus, the porosity and other properties such as tortuosity may be selected to optimise the flow within the channel. The porous material may be a nano- material and may also be conductive to improve the electro-osmotic effect. A suitable material is graphene. It is also possible to use a nano-material without an electric field. However, it is then necessary to pump the water from the production well to the injection well by creating a pressure difference between the two wells. Pumping the water may also lead to oil leakage. This may be minimised by using a hydrophilic porous material to promote the flow of water in preference to the flow of oil. Alternatively, the properties of the porous material may be adjusted to allow only water and not oil to flow.

As explained above, it is beneficial to reduce the amount of water within the production well to avoid separation processing at the well head. The arrangement of Figure 6 allows the water to be removed from the production well 310 within or at least close to the reservoir, thus reducing the length of the flow path for the water and reducing the lift required to get the fluid from the reservoir. This reduces or alleviates the need to transport water from or to the processing unit because of the local separation. Furthermore, water is added to the injection well which is beneficial for rehydrating the reservoir. Moreover, the conditions (e.g. pressure, temperature and/or flow) for separation of the oil and water may be more favourable in or near the reservoir. The barrier of Figure 5a and the electrode arrangements of Figure 2a and 2d are designed to prevent water entering the production well but nevertheless some water may enter the production well. Thus, the arrangement of Figure 6 could be used in conjunction with these arrangements to further improve the reduction of water in the injection well. For example, the barrier and channel could be used at different locations within the reservoir with the barrier being used when the injection well and the production well are spaced apart and the channel being used when they are close together.

As an alternative to providing a channel between two separate wells, the arrangements of Figures 7a to 8 can be used (either alone or in conjunction with the arrangements of Figures 2a, 2d and 5a). Figure 7a shows the injection well 322 is housed within the production well 320 (at least along part of its length). The injection well 322 is surrounded by a fluid flow controller which forms a channel 324 which is similar to the barrier of Figures 5a to 5c and thus uses the same materials. Thus the channel 324 comprises an outer layer and an inner layer between which there is a porous material. In the arrangements shown in Figures 5a and 5b, the electric field is applied so that it radiates outwards from the inner layer to the outer layer to prevent water entering. However, in this arrangement, the electric field is radiating inwards to draw water from the production well 320 into the injection well 322. The oil is unaffected by the electric field and will thus remain within the production well 320 provided that there is not a significant pressure drop between the two wells. If the pressure is lower in the injection well, it may be necessary to apply an oil phobic material (e.g. graphene) to the inner surface of the barrier (or the outer surface of the inner wall).

Figure 7b shows a variation of the barrier 324 which may be used in Figure 7a. Oil is lighter than water and the two fluids are immiscible. Accordingly, the highest concentrations of water will be found at the lowest points of the projection well. Thus, depending on the fluid levels within the production well 320, it may only be necessary to use a channel around the lower portion 326 of the injection well 322. The remaining portion 328 around the injection well is simply an impervious closed sleeve. Alternatively, the well pipe could be formed with the channel only in the lower part of the pipe wall. Figure 7c shows another variation in which there is a single well 330. In this arrangement, the well 330 is divided into two sections 334, 336 by a wall 332 which extends along the length of the well 330. The wall 332 comprises two outer electrode layers between which is a porous material such as those used in previous embodiments. One electrode is positive (marked +) and the other is negative (marked -). When an electric field is applied, electro-osmotic effect will draw water through the wall from section 334 to section 336 and thus the wall acts as a fluid flow controller. In this way, section 334 can be used as the production well and section 336 can be used as an injection well. Sections 334 and 336 can be used as transport pipes or processing equipment.

Although the wall in Figure 7c is shown as a vertical, planar wall which bisects the well; it will be appreciated that this is just one arrangement. The wall may be designed to suit the requirements of the well. For example, the wall may be planar or non-planar (e.g. curved). Furthermore, the wall may be at any angle within the well, e.g. horizontal, vertical or an angle between the two extremes. The wall may divide the well into equal sized portions for oil and water. Alternatively, if a greater volume of oil is expected, the wall may divide the well so that there is a greater section available for oil than water (or vice versa). The wall may also be flexible. Such a flexible wall may locally alter the volume of each of the production and/or injection chambers depending on the local pressure difference between the fluids at various positions.

The pressure in the injection chamber (i.e. on the water side) is preferably higher than the pressure in the production chamber (i.e. on the oil side) otherwise oil may be forced through the fluid flow controller. However, if the pressure difference is too great, the electric field will need to be very strong to overcome the pressure difference. Accordingly, the pressure difference is preferably minimised to minimise power consumption. The pressure difference may be measured and at least one outlet valve (not shown) may be provided on one or both sides of the fluid flow controller. The outlet valve(s) may be activated when the pressure difference is too great. The activation may be automatically controlled.

Figure 8 is a schematic drawing showing how the pressure within a system such as that shown in Figures 6, 7a, and 7c may be controlled. A fluid containing a mixture of oil and water flows through inlet 400 into the well 300 and the fluid is separated so that at the outlet 402, there is a greater proportion of oil (preferably predominantly only oil) in the output fluid. This is achieved using a fluid flow controller comprising a wall 332 made of a porous material which separates a first chamber 404 from a second chamber 406. Water is drawn through the wall into the first chamber 404 from the second chamber 406 by the electric field (electro osmotic pumping/flow) in the porous medium even when the pressure in the first chamber is higher than the pressure in the second chamber. One possible example implementation is that the first chamber may be used as an injection well or as a transportation pipe to remove water and the second chamber may be the production well. The chambers could also be inside transportation pipes or fluid processing units. The wall 332 may comprise an oil-phobic material alone, may comprise a combination of electrodes and porous material or may comprise a combination of electrodes and oil-phobic porous material. Where the electrodes are used to promote water flow through the porous material, a voltage is applied to the electrodes using voltage source 408.

Figure 8 shows one option for pressure control within the system which is important both when no electrodes are present and when the electrodes are present. The pressure within the first chamber, i.e. in the chamber which comprises water is maintained at a higher level than the pressure in the second chamber. If the pressure in the first chamber is too low, both oil and water will be drawn into the second chamber even if the porous material is oil-phobic and/or subject to an applied voltage. The pressure is measured in both the first and second chambers and the pressure difference between the two chambers is calculated using a pressure difference sensor 410. The measurements will normally be taken automatically, e.g. at regular intervals or alternatively on demand by a user. It will be appreciated that the pressure difference could alternatively be measured directly with a differential pressure sensor. The results of the measurements are passed to a controller 412. The pressure within the first chamber is maintained at an appropriate level by opening or closing valve 414 which controls whether or not the outlet 416 from the first chamber is open. If the controller 412 determines that the pressure is above a high threshold limit, valve 414 is opened so that water can flow through outlet 416 out of the first chamber. However, care needs to be taken to prevent too much water flowing out so that the pressure does not drop too far below the high threshold limit. Accordingly, there may also be a low threshold limit below which the pressure in the water chamber is too low and oil may be drawn therein. The valve is shut when the controller determines that the pressure difference is approaching this limit. The pressure controller (412) may adjust the valve position automatically to maintain the desired pressure difference between the two chambers.

If materials with oil phobic properties are used in the pipe, the pressure in the first chamber will normally be slightly below the pressure in the second chamber to thus enable water to flow through the oil phobic membrane.

The pressure control valve (416) may be located on the oil outlet (402), or there could be valves at both outlet (402) and the outlet of the first chamber (404). Other means could be used instead of control valves, such as pumps or other flow controlling equipment.

The unit/pipe may also consist of several sections with two chambers as shown in Figure 8. This is especially important for elevated pipes, i.e. vertical constructions. In that case the pressure difference in each section is measured and a flow control device (416) is located at each section.

The membrane between the chambers may be divided into sections where the voltage between the electrodes for each section can be controlled and the current may be measured. Monitoring the electric current enable detection of problems / clogging in that part of the unit. The voltage may be altered to clean sections with problems, i.e. deviating electric current / water flow.

The axial water flow in the upper part of the unit/pipe is a function of the axial position x, the measured electric current I, and the pressure difference between the lower and upper part of the pipe/unit, pi - p_u. A simplified water flow equation is given by q_w,u(x) = q_Wu,in - [kil - k₂(pi - p_u)]x The measured electric current I may vary with x and thus enables monitoring of the axial water flow, k-ι and k₂ are parameters.

In each of the examples of Figures 5a to 7c, the porous material between two electrodes effectively acts as a one-way valve which promotes water flow through the material from the positive to the negative electrode and prevents water flow through the material from the negative to the positive electrode.

The above embodiments are examples of the use of the electro-osmotic effect within the oil recovery process. Accordingly, the above examples use oil (hydrocarbon) and water as the fluids subject to electro-osmotic effect. However, the principle is more general and can be applied to any dipole or polar fluid (other than water) mixed with a non-dipole fluid (other than oil) provided the fluids are separable. The electro-osmotic effect may be useful for separating fluids having small differences in fluid densities. By contrast, gravitational force alone is not typically suitable for separating fluids having small differences in fluid densities (e.g. heavy oil and water).

Similarly, the above embodiments describe flow of oil and water within wells which are pipes. However, oil and water are transported in other types of pipes such as from the wells to the processing units, between processing units and from processing units to receivers or customers. Accordingly, the principles described above can be used when oil and water are flowing through all types of pipes.

Further modifications and alterations will be apparent to the skilled man. It will be understood that the invention is not limited to the described embodiments and encompasses modifications apparent to those skilled in the art lying within the spirit and scope of the claims appended hereto.

Claims

1 . A fluid flow controller for use on or inside an oil well pipe, transportation pipe and other process equipment, the fluid flow controller comprising

a positive electrode,

a negative electrode and

a porous material between the positive and negative electrodes wherein a voltage is applied to the positive and negative electrodes to generate an electric field between the electrodes to control the flow of fluid within the porous material.

2. The fluid flow controller of claim 1 , wherein the applied voltage is adjustable to control the fluid flow.

3. The fluid flow controller of claim 2, wherein the electric field E is calculated from:

U

^E = h where h is the distance between the electrodes and U is the applied voltage.

4. The fluid flow controller of any one of the preceding claims, wherein the porous material is an oilphobic material.

5. The fluid flow controller of any one of the preceding claims, wherein the properties and design of the porous material are selected to optimise oil flow through the fluid flow controller.

6. The fluid flow controller of any one of claims 1 to 4, wherein the properties and design of the porous material are selected to optimise water flow through the fluid flow controller.

7. The fluid flow controller of claim 6, wherein the applied voltage is adjustable to control the water flow with the water flow being proportional to the electric current within the porous material.

8. The fluid flow controller of claim 6 or claim 7, comprising a current sensor for measuring the current within the porous material.

9. The fluid flow controller of claim 8, wherein the voltage applied to the positive and negative electrodes is determined based on the measured current.

10. The fluid flow controller of any one of the preceding claims, wherein the fluid flow controller has a generally annular shape.

1 1 . The fluid flow controller of claim 10, wherein the positive electrode is on an inner surface of the fluid flow controller and the negative electrode on an outer surface of the fluid flow controller.

12. The fluid flow controller of claim 10, wherein the fluid flow controller has the positive electrode on an outer surface and the negative electrode on an inner surface.

13. The fluid flow controller of any one of the preceding claims, wherein the positive and negative electrode have an interchangeable polarity.

14. The fluid flow controller of claim 13, wherein the polarity of the positive and negative electrodes is changeable at regular intervals.

15. The fluid flow controller of any one of the preceding claims, comprising a plurality of fluid flow controller sections each comprising a positive electrode, a negative electrode and a porous material between the positive and negative electrodes wherein a voltage is separately applied to each of the positive and negative electrodes to generate an electric field between each of the positive and negative electrodes.

16. The fluid flow controller of claim 15, comprising a current sensor for measuring the current within the porous material of each fluid flow controller section.

17. The fluid flow controller of claim 16, wherein the voltage applied to each of the positive and negative electrodes is determined based on the measured current.

18. A fluid flow controller for use on an oil well, transportation pipe and other process equipment, the fluid flow controller comprising a porous material which is an oilphobic material

19. The fluid flow controller of any one of the preceding claims, wherein the porous material is a nano-material.

20. The fluid flow controller of claim 19, wherein the porous material is graphene.

21 . The fluid flow controller of any one of the preceding claims comprising a pressure mechanism for controlling the fluid pressure on either side of the porous material.

22. The fluid flow controller of claim 21 wherein the porous material is configured in use to separate a chamber containing a mixture of water and oil from a chamber containing water and the pressure mechanism is configured to ensure that the pressure in the chamber containing water is greater that the pressure in the chamber comprising a mixture of oil and water.

23. A production well for extracting oil from a reservoir, the production well comprising at least one fluid flow controller according to any one of claims 1 to 22.

24. The production well of claim 23 comprising a plurality of fluid flow controllers according to any one of claims 1 to 22, wherein the plurality of fluid flow controllers are spaced apart along at least part of the length of the production well.

25. The production well of claim 25, wherein the voltage applied to each of the positive and negative within each fluid flow controller is independently adjustable.

26. A transportation pipe for oil and/or water flow; the transportation pipe comprising at least one fluid flow controller according to any one of claims 1 to 22.

27. The transportation pipe of claim 26 comprising a plurality of fluid flow controllers according to any one of claims 1 to 22, wherein the plurality of fluid flow controllers are spaced apart along at least part of the length of the injection well.

28. The transportation pipe of claim 27 wherein the electric field applied to each fluid flow controller is independently adjustable.

29. An oil extraction system for extracting oil from a reservoir, the oil extraction system comprising:

an injection well for injecting fluid into the reservoir;

a production well for extracting oil from the reservoir, and

at least one fluid flow controller according to any one of claims 1 to 22.

30. The oil extraction system of claim 29, wherein the injection well is positioned within the production well along at least part of its length and the at least one fluid flow controller is on the production well whereby when a voltage is applied to the positive and negative electrodes of at least one fluid flow controller water is drawn through the fluid flow controller from the production well into the injection well.

31 . The system according to claim 30, wherein the at least one fluid flow controller comprises porous material in its lower section and is non porous elsewhere.

32. The system according to claim 29, wherein the injection well and the production well are adjacent one another along at least part of their length and the at least one fluid flow controller forms a channel between the production well and the injection well whereby when an electric field is applied to the at least one fluid flow controller, water is drawn through the channel from the production well into the injection well.

33. An oil extraction system for extracting oil from a reservoir, the oil extraction system comprising a combined injection and production well, the combined well comprising

an injection chamber for injecting fluid into the reservoir;

a production chamber for extracting oil from the reservoir, and

at least one fluid flow controller according to any one of claims 1 to 22 wherein the fluid flow controller separates the injection chamber from the production chamber.

34. The system of claim 33, wherein the at least one fluid flow controller is generally planar.

35. The system of claim 33 or claim 34, wherein the positive electrode is adjacent the production chamber and the negative electrode is adjacent the injection chamber.

36. The system of any one of claims 33 to 35, wherein the at least one fluid flow controller is flexible whereby the volume of the injection chamber and the production chamber is locally dependent on a difference in pressure between the injection chamber and the production chamber.

37. The system of claim 36 wherein the pressure difference is controlled by an outlet fluid flow controller.

38. An oil extraction system for extracting oil from a reservoir, the oil extraction system comprising:

a production well according to any one of claims 23 to 25.