GB2544757A

GB2544757A - Apparatus for generating a solution of C02 in water, for enhanced oil recovery

Info

Publication number: GB2544757A
Application number: GB1520785.5A
Authority: GB
Inventors: Najam Ali Beg Mirza; Mahmood Sarshar Mir
Original assignee: Caltec Ltd
Current assignee: Caltec Ltd
Priority date: 2015-11-25
Filing date: 2015-11-25
Publication date: 2017-05-31
Anticipated expiration: 2035-11-25
Also published as: GB201520785D0; GB2544757B

Abstract

An apparatus 10 for generating a solution of CO2 in water comprises a first jet pump 26 having a low pressure (LP) inlet 14 connected to a supply 16 of gas, a high pressure (HP) inlet 12 connected to a HP water supply 13, and an outlet 28 for a first fluid that includes a solution of CO2 in water and some CO2 gas. A first separator 30 has an inlet connected to the outlet 28 of the first jet pump to receive the first fluid, a liquid outlet 32 for a separated liquid phase comprising a first solution of CO2 in water, and a gas outlet 34 for a separated gas phase comprising CO2 gas. A second jet pump 26 has a LP 12 inlet connected to the gas outlet 34 of the first separator, a HP inlet 12 connected to a HP water supply 13, and an outlet 40 for a second fluid comprising a second solution of CO2 in water. An outlet manifold (54 figure 4) has a first manifold inlet (38 figure 4) connected to the liquid outlet of the first separator 30, a second manifold inlet (44 figure 4) connected to the outlet of the second jet pump, and an outlet 17 for an outlet fluid comprising a solution of CO2 in water. The outlet fluid comprises mixture of said first and second solutions. Later embodiments relate to a method and system for enhanced oil recovery using said apparatus.

Description

Apparatus for generating a solution of C02 in water, for enhanced oil recovery

The present invention relates to a system for, and a method of, enhanced oil recovery (EOR). In particular, but not exclusively, the invention relates to a system for and a method of enhanced oil recovery by injecting a solution of water and carbon dioxide (C02) into an oil reservoir. The invention also relates to an apparatus for generating a solution of C02 in water, for use in an EOR system. In another embodiment, the invention relates to an apparatus for increasing the production of oil from a well using a downhole jet pump. C02 is produced in many oil and gas fields, and is also generated by power generation units, often in combination with other gases such as Nitrogen. For environmental reasons, venting C02 to atmosphere is not desired, despite venting being the lowest cost method for its disposal.

Work and field experience by a number of operating oil companies has shown that injecting C02 back into the oil reservoirs with injection water enhances the sweeping efficiency of the oil in place and increases total oil recovery from the field. This system is often referred to as an EOR (Enhanced Oil Recovery) system. The C02 used in an EOR system may be produced with other gases such as Nitrogen and there are known techniques for separating it from other gases, either for disposal or for injection into the reservoir.

To enable a solution of C02 in water to be injected into an oil reservoir, the pressure of the C02 must be either above the reservoir pressure or at the water injection pressure, so that it can be injected with the water as a single phase (liquid) solution. In order to make a solution of C02 in water the pressure of the C02 gas usually has to be increased to the level needed for it to be dissolved fully in the water.

Boosting the pressure of the C02 to allow it to be fully dissolved in the injection water conventionally demands the use of a multi-stage gas compressor, resulting in high capital and operation costs. A second problem occurs when using a downhole jet pump to boost production from an oil well. Water may be used as the motive fluid to drive the jet pump and reduce the production flowing bottom hole pressure. This can increase production from the reservoir, but the resulting combination of oil and water has an increased density, which increases the hydrostatic head of fluids in the well and can limit production from the well, thereby negating most of the work done by the downhole jet pump.

It is an object of the present invention to provide an apparatus for generating a solution of C02 in water, for use in an EOR system. Another object of the invention is to provide an apparatus for and a method of enhanced oil recovery that mitigates one or more of the aforesaid problems. It is a further object of the invention to provide an apparatus for and a method of enhanced oil recovery by injecting a solution of carbon dioxide (C02) and water into an oil reservoir, preferably without the need for compressors to boost the pressure of C02 so that it can be fully dissolved in injection water. Yet another object of the invention is to provide an apparatus for increasing the production of oil from a well using a downhole jet pump.

According to one aspect of the invention there is provided an apparatus for generating a solution of C02 in water, the apparatus comprising a first jet pump having a low pressure (LP) inlet connected to a supply of C02 gas, a high pressure (HP) inlet connected to a HP water supply, and an outlet for a first fluid that includes a solution of C02 in water and some C02 gas, a first separator having an inlet connected to the outlet of the first jet pump to receive the first fluid, a liquid outlet for a separated liquid phase comprising a first solution of C02 in water, and a gas outlet for a separated gas phase comprising C02 gas, a second jet pump having a LP inlet connected to the gas outlet of the first separator, a HP inlet connected to a HP water supply, and an outlet for a second fluid comprising a second solution of C02 in water, and an outlet manifold having a first manifold inlet connected to the liquid outlet of the first separator, a second manifold inlet connected to the outlet of the second jet pump, and an outlet for an outlet fluid comprising a solution of C02 in water, wherein said outlet fluid comprises mixture of said first and second solutions.

The invention enables the production of a solution of C02 in water without requiring the use of expensive gas compressors and using only a HP water source as the motive fluid. A C02 solution can therefore be generated simply and quickly, and at minimal cost, using simple and reliable equipment.

The apparatus includes at least two pressure boosting stages (each including a jet pump), which in many situations is sufficient to ensure that substantially all the C02 gas is dissolved in the water. The solution can be provided at a high pressure, suitable for injection into a well, or its pressure can be further increased if necessary using a liquid booster pump or a positive displacement pump. The solution may be used in an EOR system or any other suitable system, or it can be used to drive a downhole jet pump. The HP water supply may for example be provided from an existing HP water supply, thus avoiding the need to boost the pressure of the water supply. The LP C02 gas may, for example, be supplied from any suitable source including, for example, the exhaust gases of an on-site power supply plant or from separated well gases.

The apparatus may include a first liquid pump connected between the liquid outlet of the first separator and the first manifold inlet, for boosting the pressure of the first solution. The apparatus may include a second liquid pump connected between the outlet of the second jet pump and the second manifold inlet, for boosting the pressure of the second solution. The first and second liquid pumps may for example be liquid booster pumps or positive displacement pumps, and can be used for boosting the pressure of the first and second solutions, for example to the well pressure in an EOR system.

The first separator may comprise a uniaxial cyclonic separator, which is compact and provides a high level of phase separation with minimal loss of fluid pressure.

In an embodiment, the second fluid comprises a solution of C02 in water and some C02 gas, and the apparatus further comprises a second separator having an inlet connected to the outlet of the second jet pump to receive the second fluid, a liquid outlet for a separated liquid phase comprising said second solution of C02 in water, and a gas outlet for a separated gas phase comprising C02 gas, a third jet pump having a LP inlet connected to the gas outlet of the second separator, a HP inlet connected to a HP water supply, and an outlet for a third fluid comprising a third solution of C02 in water, wherein the outlet manifold has a third manifold inlet connected to the outlet of the third jet pump, and wherein the second manifold inlet is connected to the outlet of the second jet pump via the liquid outlet of the second separator, said outlet fluid comprising mixture of said first, second and third solutions.

In this embodiment the apparatus comprises at least three pressure boosting stages, which in most cases ensures complete dissolving of all available C02 gas.

The second separator may comprise a uniaxial cyclonic separator, which provides the same advantages as the first separator, as described above.

The apparatus may further comprise a third liquid pump connected between the outlet of the third jet pump and the third manifold inlet, for boosting the pressure of the third solution. The third liquid pump may for example be a liquid booster pump or a positive displacement pump.

According to another aspect of the invention there is provided a system for enhanced oil recovery, comprising an apparatus according to any one of the preceding statements of invention for generating a solution of C02 in water, an injection well for injecting the solution into an oil reservoir, and a production well for drawing produced fluids from the oil reservoir.

The dissolved C02 gradually comes out of solution after the solution has been injected into the reservoir and its pressure drops as water passes through reservoir pores, which promotes the movement of produced fluids towards the production well, thereby providing for enhanced oil recovery from the well. The system may make use of existing resources already available at the site of the production well, including for example a HP water supply and a source of C02 gas.

According to another aspect of the invention there is provided a system for drawing produced fluids from an oil reservoir, comprising an apparatus according to any one of the preceding statements of invention for generating a solution of C02 in water, a production well comprising a well bore having a lower end in fluid communication with the oil reservoir and an upper end that comprises an outlet for produced fluids, and a downhole jet pump located towards the lower end of the well bore, wherein the downhole jet pump has a HP inlet connected to receive a HP solution of C02 in water from the apparatus, a LP inlet connected to receive produced fluids from the oil reservoir, a nozzle configured to inject the HP solution into the produced fluids, and an outlet for a mixture of fluids comprising the produced fluids and the solution of C02 in water, wherein the outlet of downhole jet pump is configured to discharge the mixture of fluids into the well bore for delivery to the upper end of the well bore.

The downhole jet pump reduces the back pressure at the bottom of the well bore, leading to increased production. The dissolved C02 gas comes out of solution downstream of the downhole jet pump as the solution is injected into the produced fluids and acts as a lift gas to further boost production by reducing the hydrostatic head of fluids along the well bore and thus reducing the back pressure on the well at reservoir level. The need for a separate gas injection line is thus avoided.

The nozzle of the downhole jet pump may be configured to provide a pressure drop in the solution of C02 in water flowing through the nozzle, so as to cause the C02 to come at least partially out of solution, thereby generating bubbles of C02 gas in the produced fluids flowing towards the upper end of the well bore. This enables the C02 gas to act as a lift gas.

According to another aspect of the invention there is provided a method for generating a solution of C02 in water, the method comprising providing a first jet pump, supplying C02 gas to a low pressure (LP) inlet of the first jet pump, and supplying high pressure (HP) water to a HP inlet of the first jet pump to produce a first fluid that includes a solution of C02 in water and some C02 gas, providing a first separator, delivering the first fluid to an inlet of the first separator, and separating the first fluid to provide a liquid phase comprising a first solution of C02 in water and a gas phase comprising C02 gas, providing a second jet pump, delivering the separated gas phase to an LP inlet of the second jet pump, and supplying HP water to a HP inlet of the second jet pump to produce a second fluid comprising a second solution of C02 in water, and mixing the first and second solutions to produce an outlet fluid comprising a solution of C02 in water.

The method may further comprise boosting the pressure of the first solution with a first liquid displacement pump.

The method may further comprise boosting the pressure of the second solution with a second liquid pump.

The method may further comprise delivering the second fluid to an inlet of a second separator and separating a liquid phase comprising said second solution of C02 in water from a gas phase comprising C02 gas, providing a third jet pump, delivering the separated gas phase from the second separator to a LP inlet of the third jet pump, supplying HP water to an HP inlet of the third jet pump to produce a third fluid comprising a third solution of C02 in water, and combining said first, second and third solutions to provide an outlet fluid comprising mixture of said first, second and third solutions.

The method may further comprise boosting the pressure of the third solution with a third liquid pump.

According to another aspect of the invention there is provided a method of enhanced oil recovery, comprising generating a solution of C02 in water by a method according to any one of the preceding statements of invention, injecting the solution into an oil reservoir through an injection well, and drawing produced fluids from the oil reservoir through a production well.

According to another aspect of the invention there is provided a method drawing produced fluids from an oil reservoir, comprising generating a solution of C02 in water by a method according to any one of the preceding statements of invention, providing a production well comprising a well bore having a lower end in fluid communication with the oil reservoir and an upper end for produced fluids, locating a downhole jet pump towards the lower end of the well bore, delivering a HP solution of C02 in water to a HP inlet of the downhole jet pump, receiving produced fluids from the oil reservoir into a LP inlet of the downhole jet pump, and injecting the HP solution into the produced fluids through a nozzle of the downhole jet pump to produce a mixture of fluids comprising the produced fluids and the solution of C02 in water, and discharging the mixture of fluids into the well bore with some of the C02 as a gas phase for delivery to the upper end of the well bore.

The method may further comprise providing a pressure drop in the solution of C02 in water flowing through the nozzle of the downhole jet pump, thereby causing the C02 to come at least partially out of solution and generating bubbles of C02 gas in the produced fluids flowing towards the upper end of the well bore.

According to one embodiment, the invention involves the use of jet pumps or eductors to boost the pressure of C02, thus avoiding the need for multi-stage gas compressors, which may cost several times more than the jet pumps. Preferably, this method makes use of available high pressure injection water as the high pressure motive flow for the jet pumps. The C02 in this case will be dissolved in the injection water and pumped into the reservoir, and when injected into the reservoir the C02 can be released gradually so that it helps to sweep the remaining oil in the reservoir towards the production well, thus improving total recovery from the oil field. In this way the cost of boosting the pressure of the C02 and injecting it into the reservoir can be recovered from the added revenue generated by the increased recovery of the oil in place and in many cases by not having to pay penalties for releasing C02 to atmosphere. Some of the injected C02 may be sequestered underground, and therefore use of the method also enables the operator to avoid paying penalties for release of C02 to atmosphere. The C02 may be generated from systems that burn fuel to generate electricity or for use in operations onshore or offshore, and the produced C02 can then be dissolved in injection water for injection into oil or gas reservoirs.

The system used for dissolving C02 in injection water generally requires two or three pressure boosting stages (PBSs), using jet pumps, to dissolve the C02 fully in the injection water. However, in some cases just one PBS or more than three PBSs may be required.

Theory and experience have shown that high pressure water, used as the motive flow for a jet pump, enables a relatively high level of boost in the pressure of low pressure C02 gas to be achieved. By way of example, Figure 1 illustrates the level of boost in the pressure of a gas that can be achieved for every one million standard cubic feet of gas per day (lmmscfd) at different water flow rates, measured in barrels per day (bbl/d).

The amount of C02 that can be dissolved in water depends on the pressure of the system and the C02 flow rate: the higher the pressure of C02 and water, the higher will be the amount of C02 that can be dissolved in water. For this reason the C02 cannot be fully dissolved in a single pressure boosting stage based on the usual injection pressure of injection water. As an example if the pressure of the C02 is increased from near atmospheric pressure to 12 barg (bar gauge), up to 60% of the C02 can be dissolved in water. However, if the pressure of the remaining C02 is increased to 21 barg, then the entire remaining amount of C02 can be dissolved in water. Boosting the pressure of C02 from one atmosphere to 21 barg or higher with one jet pump requires a high flow rate of water. Using two or three jet pump stages reduces the flow rate of water required for each stage and also helps to ensure better dissolving of the C02 in the injection water.

The use of a jet pump offers two benefits: 1- The jet pump boosts the pressure of the C02 in a passive way without the need for a compressor, 2- The jet pump generates good mixing of the C02 with the water, which enhances and maximises the efficiency with which C02 is dissolved in the water. C02 gas requires a specific pressure to be dissolved in water at a specific rate, and depending on its original pressure, two or three pressure boosting stages, using jet pumps, may be required to dissolve the C02 fully in the injection water. The original pressure of the C02 can be as low as near atmospheric pressure, or it can have an initial pressure of a few barg, which may then permit the use of fewer pressure boosting stages using jet pumps to dissolve the C02 fully in the water.

As more than one pressure boosting stage is generally needed to dissolve all the C02 in the injection water, a separator may be needed between the successive pressure boosting stages to separate the undissolved C02 and pass it on to the next pressure boosting stage, so that its pressure can be increased further, allowing more C02 to be dissolved in the water.

The separator can be a conventional vertical or horizontal gravity separator, but to achieve a more compact and lighter weight solution, it may be a compact uniaxial cyclonic separator, for example a separator of the type sold by Caltec Limited under the trade mark l-SEP, as described in US patent No. 6,398,973. Alternatively, any other inline compact separator that is capable of separating gas from liquid may be used. In general, the maximum number of pressure boosting stages required to boost the C02 pressure and dissolve it fully in the water will be three, but in some cases, for example where the C02 is already at an initial pressure of a few barg, two pressure boosting stages may be sufficient.

The outlet pressure of the solution can if required be further increased by using a liquid pump (for example a liquid booster pump or a positive displacement (PD) pump), allowing the C02/water solution to be injected into deep reservoirs or wellbores. Centrifugal pumps may act as feed pumps to a PD pump. The use of a PD pump is preferred, as if a compact separator is used to separate remaining C02 from water, the compact separator may allow some C02 to be carried through with the water phase and some liquid pumps cannot tolerate free gas in the liquid phase which they handle.

In another application that uses a HP solution of water with dissolved C02, the solution is sent downhole to the bottom of a producing oil well where a downhole jet pump is installed. The downhole jet pump receives the solution of injection water and C02 as the motive flow and operates in a similar manner to a conventional downhole jet pump to boost the pressure of the produced fluids. However, in this case, as the pressure of the injected water drops downstream of the HP nozzle, it pulls in the produced oil, but at the same time it releases some of the dissolved C02. This released gas acts as a gas lift, reducing the hydrostatic head of fluids flowing through the well bore and reducing the production flowing bottom-hole pressure (FBHP), thus increasing production. This system therefore offers two benefits: a- it eliminates the need to inject gas separately as the lift gas, and b- as the HP feed to the jet pump is a liquid instead of gas, it reduces the downhole back pressure on the well to increase production.

Certain embodiments of the invention will now be described by way of example with reference to the accompanying drawings, wherein:

Figure 1 is a graph showing the relationship between the discharge pressure and the high pressure water inlet flow rate in a jet pump with high pressure water driving low pressure gas at different water inlet pressures;

Figure 2 is a schematic diagram of an enhanced oil recovery system, comprising a first embodiment of the invention;

Figure 3 is a schematic diagram of an apparatus for generating a solution of C02 in water for use in an enhanced oil recovery system, comprising a second embodiment of the invention;

Figure 4 is a schematic diagram of an apparatus for generating a solution of C02 in water for use in an enhanced oil recovery system, comprising a third embodiment of the invention, and

Figure 5 is a schematic cross-sectional view of an apparatus for increasing the production of oil from a well using a downhole jet pump, comprising a fourth embodiment of the invention.

The enhanced oil recovery (EOR) system shown in Figure 2 comprises a production well 4 and an injection well 6, which are drilled into different parts of an underground oil reservoir 8. An apparatus 10 for generating an injection solution of C02 and water is connected to the injection well 6, allowing a high pressure injection solution to be pumped into the oil reservoir 8. This helps to drive oil in the reservoir 8 towards the production well 4, so that the produced fluids can then flow to the surface through the production well 4.

The apparatus 10 for generating an injection solution has a first inlet 12 that receives high pressure water, for example injection water, from a HP water supply 13 and a second inlet 14 for C02 gas. The C02 gas inlet 14 is connected to a supply 16 of C02 gas, which may for example be connected to receive C02 gas derived from the exhaust gases of the fuel-burning power generation unit. The solution generating apparatus 10 has an outlet 17 for the generated solution of C02 and water, which is connected to the top of the injection well 6, allowing the injection solution to be injected into the reservoir 8.

The production well 4 is connected to a separator 18 for separating the produced fluids, the separator 18 having a first outlet 20 for liquids (including the produced oil) and a second outlet 22 for gases (including hydrocarbon gas and separated C02 gas). The separator 18 may be any suitable gas/liquid separator, typically a horizontal or vertical gravity separator, or it may be a cyclonic separator, for example a uniaxial cyclonic separator of the type sold by Caltec Limited under the trade mark l-SEP, as described in US 6,398,973.

The embodiment shown in Figure 3 comprises an injection solution generating apparatus 10, for generating a solution of C02 in water, which may for example be used in the EOR system shown in Figure 2, or the production boosting apparatus shown in Figure 5.

The injection solution generating apparatus 10 shown in Figure 3 includes first and second inlets 12, 12' connected to a supply 13 of high pressure (HP) water, e.g. injection water, a low pressure (LP) inlet 14 that is connected to a supply 16 of C02 gas and an outlet 17 for the generated injection solution. The first HP water inlet 12 is connected to the HP inlet of a first liquid-gas jet pump 26, and the C02 gas inlet 14 is connected to the low pressure inlet of the jet pump 26. The HP water flowing through the HP water inlet 12 serves as the motive fluid for the jet pump 26, which increases the pressure of the LP C02 gas drawn through the LP inlet 14 into the jet pump 26. At least some of the C02 gas is dissolved in the water, producing a C02/water solution, which exits the first jet pump 26 through a first fluid outlet line 28.

The fluid in the first fluid outlet line 28 may also contain some bubbles of undissolved C02 gas. This fluid in the first fluid outlet line 28 is fed to a separator 30, which separates the gas and liquid phases of the fluid and delivers the separated liquid phase into a liquid outlet line 32, and the separated C02 gas phase into a gas outlet line 34. The separated liquid phase, comprising a solution of C02 in water, flows through the liquid outlet line 32 into a first liquid pump 36, for example a liquid boosting pump or a positive displacement pump, which increases the pressure of the solution and delivers it through a high pressure delivery line 38 to the injection solution outlet 17.

The separator 30 may be any suitable gas/liquid separator, for example a horizontal or vertical gravity separator, or it may be a cyclonic separator, for example a uniaxial cyclonic separator of the type sold by Caltec Limited under the trade mark l-SEP, as described in US 6,398,973.

The separated gas phase is fed from the separator 30 through the gas outlet line 34 to the LP inlet of a second liquid-gas jet pump 26'. HP water, for example injection water, is fed to the HP inlet of the second jet pump 12' through the second HP water inlet 12'. The HP water flowing through the second HP water inlet 12' serves as the motive fluid for the second jet pump 26', which increases the pressure of the LP C02 gas drawn through the gas outlet line 34 into the second jet pump 26'. The second jet pump 26' increases the pressure of the C02 gas, which as a result is dissolved in the water, producing a C02/water solution. This solution exits the second jet pump 26' through a second fluid outlet line 40 and then flows into a second liquid pump 42, which increases the pressure of the solution and delivers it through a second high pressure delivery line 44 to the injection solution outlet 17, where it is combined with the solution delivered through the first HP delivery line 38.

The high pressure C02/water solution flowing through the injection solution outlet 17 is then injected into the oil reservoir 8 through the injection well 6, thereby enhancing the delivery of oil from the production well 4.

The injection solution generating apparatus 10 shown in Figure 4 is similar to that shown in Figure 3, except that it has three pressure boosting stages instead of two pressure boosting stages.

The apparatus 10 includes first and second inlets 12, 12' connected to a supply 13 of high pressure (HP) water, e.g. injection water, a low pressure (LP) inlet 14 that is connected to a supply 16 of C02 gas and an outlet 17 for the generated injection solution. The first HP water inlet 12 is connected to the HP inlet of a first liquid-gas jet pump 26, and the C02 gas inlet 14 is connected to the low pressure inlet of the first jet pump 26. The HP water flowing through the HP water inlet 12 serves as the motive fluid for the jet pump 26, which increases the pressure of the LP C02 gas drawn through the LP inlet 14 into the first jet pump 26. At least some of the C02 gas is dissolved in the water, producing a C02/water solution, which exits the first jet pump 26 through a first fluid outlet line 28.

The fluid in the first fluid outlet line 28 may also contain some bubbles of undissolved C02 gas. This fluid in the first fluid outlet line 28 is fed to a first separator 30, which separates the gas and liquid phases of the fluid and delivers the separated liquid phase into a liquid outlet line 32, and the separated C02 gas phase into a gas outlet line 34. The separated liquid phase, comprising a solution of C02 in water, flows through the liquid outlet line 32 into a first liquid pump 36, which increases the pressure of the solution and delivers it through a high pressure delivery line 38 to the injection solution outlet 17, via a manifold 54.

The first separator 30 may be any suitable gas/liquid separator, for example a horizontal or vertical gravity separator, or it may be a cyclonic separator, for example a uniaxial cyclonic separator of the type sold by Caltec Limited under the trade mark l-SEP, as described in US 6,398,973.

The separated gas phase is fed from the first separator 30 through the gas outlet line 34 to the LP inlet of a second liquid-gas jet pump 26'. HP water, for example injection water, is fed from the water supply 13 to the HP inlet of the second jet pump 12' through the second HP water inlet 12'. The HP water flowing through the second HP water inlet 12' serves as the motive fluid for the second jet pump 26', which increases the pressure of the LP C02 gas drawn through the gas outlet line 34 into the second jet pump 26'. The second jet pump 26' increases the pressure of the C02 gas, which as a result is dissolved in the water, producing a C02/water solution. This solution exits the second jet pump 26' through a second fluid outlet line 40 and then flows into a second positive displacement pump 42, which increases the pressure of the solution and delivers it through a second high pressure delivery line 44 to the injection solution outlet 17, via manifold 54, where it is combined with the solution delivered through the first HP delivery line 38.

The solution in the second fluid outlet line 40 may contain some remaining bubbles of undissolved of C02 gas. This fluid is fed to a second separator 30' which separates the gas and liquid phases of the fluid and delivers the separated liquid phase into a second liquid outlet line 41, and delivers the separated C02 gas into a second gas outlet line 46. The separated liquid phase, comprising a solution of C02 gas in water, flows through the second liquid outlet line 41 into a second liquid pump 42, which increases the pressure of the solution and delivers it through a high pressure delivery line 44 to the injection solution outlet 17, via manifold 54.

The separated gas phase is fed from the second separator 30' through the gas outlet line 46 to the low pressure inlet of a third liquid gas jet pump 26". High pressure water, for example injection water, is fed to the HP inlet of the third jet pump 26" through the second HP water inlet 12".

The HP water flowing through the HP water inlet 12" serves as the motive fluid for the third jet pump 26", which increases the pressure of the C02 gas drawn through the LP inlet 46 into the third jet pump 26". The C02 gas is dissolved in the water, producing a C02/water solution, which exits the third jet pump 26" through a third fluid outlet line 48. This solution then flows through the third outlet line 48 into a third liquid pump 50, which increases the pressure of the solution and delivers it through a high pressure fluid delivery line 52 to the injection solution outlet 17, via manifold 54. The first, second and third liquid pumps 36, 42, 50 may each for example be a liquid boosting pump or a positive displacement pump.

Figure 5 illustrates a production boosting apparatus 60 for increasing the production of oil from a production well 4 using a downhole jet pump. The production boosting apparatus 60 includes a cylindrical tubing 62 that is located coaxially within a well bore 64, providing an annular space 68 between the tubing 62 and the casing 66 of the well bore 64. A packer 70 is positioned in the annular space 68 towards the lower end of the tubing 62, which divides the annular space 68 into an upper part 68' and a lower part 68". The lowest part 72 of the well bore 64 is located within an oil reservoir 74, allowing oil to flow from the reservoir 74 into the lowest portion 72 of the well.

The lowest portion of the cylindrical tubing 62 houses a liquid-liquid jet pump 76 having a nozzle 77 that is connected to a high pressure inlet 78, which opens into the upper part 68' of the annular space 68, just above the packer 70. The liquid-liquid jet pump 76 also has a low pressure inlet 80 comprising a plurality of slots provided in the lowest part of the cylindrical tubing 62, below the packer 70, which open into the lowest part 72 of the well bore 64. The liquid-liquid jet pump 76 also includes a mixing tube 82 and a diffuser 84, which are located within the cylindrical tubing 62, above the nozzle 77.

In use, a motive fluid comprising a high pressure solution of water and dissolved C02 is introduced from the top of the well bore 64 into the annular space 68 between the tubing 62 and the peripheral casing 66 of the well bore. The HP fluid flows downwards through the annular space 68 and enters the HP inlet 78 of the liquid-liquid jet pump 76. At the same time, oil flows into the lowest part 72 of the well from the oil reservoir 74, and into the LP inlet 80.

As the motive fluid flows through the nozzle 77 it causes a drop in pressure, which draws oil from the lowest part 72 of the well into the mixing tube 82. The motive fluid and the oil then mix and flow through the diffuser 84, and then continue upwards through the cylindrical tubing 62 to the top of the well bore 64.

The drop in pressure experienced by the motive fluid as it passes through the nozzle 77 causes at least some of the dissolved C02 to come out of solution and effervesce, forming bubbles of C02 that mix with the oil within the jet pump 76 and the cylindrical tubing 62. The gas bubbles reduce the density of the fluids flowing upwards though the tubing 62, reducing the hydrostatic head of the fluids flowing through the well bore and reducing the production flowing bottom-hole pressure, thereby increasing oil production. The C02 gas may if required be separated from the produced fluids at the top of the well bore, for example using a cyclonic separator. The separated C02 gas can then be dissolved in high pressure water, for example using an apparatus as shown in Figure 3 or Figure 4, and this solution can then be reused as a motive fluid to drive the jet pump 76.

As an alternative solution, the downhole jet pump may be carried by a coil tubing. In that case the annulus 68 will be the space between the coil tubing and the well casing 66.

Claims

1. An apparatus for generating a solution of C02 in water, the apparatus comprising: a. a first jet pump having a low pressure (LP) inlet connected to a supply of C02 gas, a high pressure (HP) inlet connected to a HP water supply, and an outlet for a first fluid that includes a solution of C02 in water and some C02 gas, b. a first separator having an inlet connected to the outlet of the first jet pump to receive the first fluid, a liquid outlet for a separated liquid phase comprising a first solution of C02 in water, and a gas outlet for a separated gas phase comprising C02 gas, c. a second jet pump having a LP inlet connected to the gas outlet of the first separator, a HP inlet connected to a HP water supply, and an outlet for a second fluid comprising a second solution of C02 in water, and d. an outlet manifold having a first manifold inlet connected to the liquid outlet of the first separator, a second manifold inlet connected to the outlet of the second jet pump, and an outlet for an outlet fluid comprising a solution of C02 in water, said outlet fluid comprising mixture of said first and second solutions.

2. An apparatus according to claim 1, further comprising a first liquid pump connected between the liquid outlet of the first separator and the first manifold inlet, for boosting the pressure of the first solution.

3. An apparatus according to claim 1 or claim 2, further comprising a second liquid pump connected between the outlet of the second jet pump and the second manifold inlet, for boosting the pressure of the second solution.

4. An apparatus according to any one of the preceding claims, wherein the first separator comprises a uniaxial cyclonic separator.

5. An apparatus according to any one of the preceding claims, wherein the second fluid comprises a solution of C02 in water and some C02 gas, the apparatus further comprising: a. a second separator having an inlet connected to the outlet of the second jet pump to receive the second fluid, a liquid outlet for a separated liquid phase comprising said second solution of C02 in water, and a gas outlet for a separated gas phase comprising C02 gas, b. a third jet pump having a LP inlet connected to the gas outlet of the second separator, a HP inlet connected to a HP water supply, and an outlet for a third fluid comprising a third solution of C02 in water, and c. wherein the outlet manifold has a third manifold inlet connected to the outlet of the third jet pump, and wherein the second manifold inlet is connected to the outlet of the second jet pump via the liquid outlet of the second separator, said outlet fluid comprising mixture of said first, second and third solutions.

6. An apparatus according to claim 5, wherein the second separator comprises a uniaxial cyclonic separator.

7. An apparatus according to claim 5 or claim 6, further comprising a third liquid pump connected between the outlet of the third jet pump and the third manifold inlet, for boosting the pressure of the third solution.

8. A system for enhanced oil recovery, comprising an apparatus according to any one of the preceding claims for generating a solution of C02 in water, an injection well for injecting the solution into an oil reservoir, and a production well for drawing produced fluids from the oil reservoir.

9. A system for drawing produced fluids from an oil reservoir, comprising an apparatus according to any one of claims 1 to 7 for generating a solution of C02 in water, a production well comprising a well bore having a lower end in fluid communication with the oil reservoir and an upper end that comprises an outlet for produced fluids, and a downhole jet pump located towards the lower end of the well bore, wherein the downhole jet pump has a HP inlet connected to receive a HP solution of C02 in water from the apparatus, a LP inlet connected to receive produced fluids from the oil reservoir, a nozzle configured to inject the HP solution into the produced fluids, and an outlet for a mixture of fluids comprising the produced fluids and the solution of C02 in water, wherein the outlet of downhole jet pump is configured to discharge the mixture of fluids into the well bore for delivery to the upper end of the well bore.

10. A system according to claim 10, wherein the nozzle of the downhole jet pump is configured to provide a pressure drop in the solution of C02 in water flowing through the nozzle, so as to cause the C02 to come at least partially out of solution, thereby generating bubbles of C02 gas in the produced fluids flowing towards the upper end of the well bore.

11. A method for generating a solution of C02 in water, the method comprising: a. providing a first jet pump, supplying C02 gas to a low pressure (LP) inlet of the first jet pump, and supplying high pressure (HP) water to a HP inlet of the first jet pump to produce a first fluid that includes a solution of C02 in water and some C02 gas, b. providing a first separator, delivering the first fluid to an inlet of the first separator, and separating the first fluid to provide a liquid phase comprising a first solution of C02 in water and a gas phase comprising C02 gas, c. providing a second jet pump, delivering the separated gas phase to an LP inlet of the second jet pump, and supplying HP water to a HP inlet of the second jet pump to produce a second fluid comprising a second solution of C02 in water, and d. mixing the first and second solutions to produce an outlet fluid comprising a solution of C02 in water.

12. A method according to claim 11, further comprising boosting the pressure of the first solution with a first liquid pump.

13. A method according to claim 11 or claim 12, further comprising boosting the pressure of the second solution with a second liquid pump.

14. A method according to any one of claims 11 to 13, further comprising: a. delivering the second fluid to an inlet of a second separator and separating a liquid phase comprising said second solution of CO2 in water from gas phase comprising C02 gas, b. providing a third jet pump, delivering the separated gas phase from the second separator to a LP inlet of the third jet pump, supplying HP water to an HP inlet of the third jet pump to produce a third fluid comprising a third solution of C02 in water, and c. combining said first, second and third solutions to provide an outlet fluid comprising mixture of said first, second and third solutions.

15. A method according to claim 14, further comprising boosting the pressure of the third solution with a third liquid pump.

16. A method of enhanced oil recovery, comprising generating a solution of C02 in water by a method according to any one of claims 11 to 15, injecting the solution into an oil reservoir through an injection well, and drawing produced fluids from the oil reservoir through a production well.

17. A method drawing produced fluids from an oil reservoir, comprising generating a solution of C02 in water by a method according to any one of claims 11 to 15, providing a production well comprising a well bore having a lower end in fluid communication with the oil reservoir and an upper end for produced fluids, locating a jet pump towards the lower end of the well bore, delivering a HP solution of C02 in water to a HP inlet of the downhole jet pump, receiving produced fluids from the oil reservoir into a LP inlet of the downhole jet pump, and injecting the HP solution into the produced fluids through a nozzle of the downhole jet pump to produce a mixture of fluids comprising the produced fluids and the solution of C02 in water, and discharging the mixture of fluids into the well bore for delivery to the upper end of the well bore.

18. A method according to claim 17, further comprising providing a pressure drop in the solution of C02 in water flowing through the nozzle, thereby causing the C02 to come at least partially out of solution and generating bubbles of C02 gas in the produced fluids flowing towards the upper end of the well bore.