Method and system for oil and water separation utilizing a hydrostatic pressure head for disposal of water

Abstract

A method and system for the downhole separation of a water and oil mixture and disposal of separated water utilizing a hydrostatic pressure head is disclosed. A separator apparatus is located in a wellbore at a depth substantially above a water disposal formation. A mixture of oil and water is received from an oil producing formation and delivered to the separator apparatus. The oil and water mixture is separated into separated water and separated oil by the separator apparatus. The separated oil is delivered to the well surface. The separated water is discharged from the separator apparatus into the wellbore creating a column of water above the water disposal formation. The hydrostatic pressure created by the column of water is ideally sufficient to cause the separated water to dissipate into the water disposal formation. Alternatively, an auxiliary disposal pump may also be used to augment the hydrostatic pressure in the wellbore to further cause dissipation of the separated water into the water disposal formation.

Description

FIELD OF INVENTION

[0001] This invention relates generally to oil well production, and more particularly, to systems and methods for separating oil and water in wellbores so that substantially only oil is produced to well surfaces.

BACKGROUND OF THE INVENTION

[0002] During the production of hydrocarbon fluids from an oil well, separation of water from hydrocarbons is typically done after the water and hydrocarbons are produced to a well's surface. The separated water must then be disposed of in accordance with standard oilfield practices and local regulations. In many areas, this involves re-injecting the produced water into a dedicated injection well. This method not only requires an additional well, but large amounts of costly surface mounted separation and injection equipment.

[0003] One manner of addressing drawbacks associated with surface separation and disposal of water is to separate hydrocarbon fluids from water, and other contaminants, down in the wellbore of a well. Ideally, the desired hydrocarbons are produced to the well's surface while the contaminants are reinjected into formations adjacent the wellbore. As the contaminants are disposed of without ever coming to the surface of the earth, or to an offshore platform, or even to an ocean floor, environmental concerns associated with the disposal of the contaminants are substantially reduced. Similarly, large expenditures related to the surface separation and disposal of these contaminants is avoided.

[0004] An example of such a downhole separation system is described in U.S. Pat. No. 4,241,787 to Price. This separation system is placed in a wellbore adjacent to a producing formation containing an oil and water mixture. This mixture is received in the wellbore and passed to the separation system. The separation system includes a membrane separator, a crude oil pump and a brine pump. The membrane allows water to readily permeate there through while inhibiting the passage of oil. The crude oil pump is used to pump separated oil to a well surface. Concurrently, the brine pump is utilized to drive water into a disposal formation in fluid communication with the well bore.

[0005] This particular separation system has a number of drawbacks. First, the separation system is quite complex as it contains both a brine pump and an oil pump. Substantial plumbing is required to interconnect the passages of this separation system. Consequently, the separation system is expensive to manufacture and is more prone to failure than a simpler system. Further, as the brine pump is disposed adjacent to the oil producing formation, the brine pump must provide the primary force to dissipate the separated salt water into the disposal formation. Moreover, as the separation system is disposed deep down in a wellbore, great expense and time is needed to withdraw and reinstall the separation system when servicing is required.

[0006] Accordingly, there is a need for a simplified separation system which overcomes many of the aforementioned shortcomings of previous downhole separation systems.

SUMMARY OF THE INVENTION

[0007] It is an object of the present to provide a downhole separation system and method of using the same which utilizes a separator apparatus which is located in a wellbore above a water disposal formation whereby separated water may be disposed of into the disposal formation substantially under the influence of gravity or hydrostatic pressure.

[0008] It is another object to provide a separation system that is simplified compared to previously used downhole separation systems.

[0009] It is yet another object to provide a downhole separation system wherein only a single primary pump is required to provide sufficient lift to a water and oil mixture to lift the mixture to a separator apparatus, induce separation, and then further convey the separated oil to a well surface.

[0010] A further object is to provide a separation system for wellbore separation of hydrocarbons from water in a wellbore using a separator apparatus that is easily accessible for maintenance and repair.

[0011] The present invention is directed to a method and system for separating water and oil in a wellbore and disposing of the separated water into an underground water disposal formation. The wellbore extends from a well surface to a water disposal formation and to an oil producing formation. A packer in the wellbore separates the water disposal formation and the oil producing formation. A separator apparatus is ideally placed in the wellbore at a height substantially above the water disposal formation and preferably, also above the oil producing formation. A production string disposed within the wellbore includes a first segment that receives the water and oil mixture from the oil producing formation and transports the mixture to the separator apparatus. A second segment of the production string is used to transport the separated oil from the separator apparatus to the surface of the well. The separator apparatus substantially separates the water and oil mixture into separated water and separated oil. The separated water ideally passively flows from the separator apparatus to create a column of water in the wellbore above the disposal formation. The hydrostatic pressure created by the column of water helps the water dissipate into the water disposal formation. Meanwhile the separated oil is passed through the second segment of the production string to the well surface for treatment or storage. Ideally, the separator apparatus includes a membrane to separate the water and oil mixture. Preferably, only a single conventional pump disposed near the oil producing formation is needed to provide sufficient lift to pump the water and oil mixture to the separator apparatus and further to lift the separated oil to the well surface.

[0012] The invention also includes forming a sealed water disposal chamber in the wellbore. The sealed water disposal chamber preferably includes the column of water to create a hydrostatic pressure head. An auxiliary pump may be used to augment the pressure in the water disposal chamber when there is not sufficient hydrostatic pressure to dissipate the separated water into the water disposal formation.

[0013] This invention further includes the separating of a water and oil mixture into separated water and separated oil on the surface of a well from which the mixture was produced. Separated water and contaminants are then disposed of down into the same producing wellbore. Hydrostatic pressure, and possibly auxiliary pressure provided by a pump, is then utilized to dissipate the separated water into a downhole disposal formation.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] These and other objects, features and advantages of the present invention will become better understood with regard to the following description, pending claims and accompanying drawings where:

[0015] FIG. 1 is an exemplary schematic sectional view of a separation system, made in accordance with the present invention, which utilizes a separator apparatus to separate water and oil in a wellbore and which disposes of the separated water utilizing a column of water to create a hydrostatic pressure head;

[0016] FIG. 2 is an exemplary schematic sectional view of one type of separator apparatus that may be used with the system of FIG. 1;

[0017] FIG. 3 is an exemplary schematic sectional view of a second embodiment of a separation system similar to the system of FIG. 1 which is augmented with an auxiliary disposal pump to assist in the disposal of separated water; and

[0018] FIG. 4 is an exemplary schematic sectional view of a third embodiment, made in accordance with the present invention, wherein a water disposal formation is located beneath an oil producing formation.

DETAILED DESCRIPTION OF THE INVENTION

[0019] FIG. 1 shows a separation system 10 made in accordance with a first exemplary embodiment of the present invention. System 10 includes a wellbore 12 that extends downwardly from a well surface 14 and fluidly connects with a first water disposal formation 16 and a second oil producing formation 18. In this particular embodiment, water disposal formation 16 is located above oil producing formation 18. Oil producing formation 18 contains a mixture of oil and water along with other constituents and contaminants such as natural gas, particulates, hydrogen sulfide, carbon dioxide, etc. A packer 20 is placed in wellbore 12 to isolate oil producing formation 18 from water disposal formation 16. Packer 20 is ideally equipped with a gas vent (not shown) to allow free gas from oil producing formation 18 to pass upwardly into wellbore 12. However, a non-vented packer will still allow system 10 to operate. Wellbore 12 includes perforations 22 that allow the water and oil mixture from oil producing formation 18 to enter wellbore 12. Similarly, wellbore 12 has perforations 24 that allow separated water to dissipate from wellbore 12 into water disposal formation 16. A wellhead 25 provides closure to the upper end of wellbore 12.

[0020] A separator apparatus 26 is interposed in a production string 28 of tubing that is disposed within wellbore 12. An upper segment 30 of production string 28 extends from the well surface 14 to separator apparatus 26. A second lower segment 32 of production string 28 extends from separator apparatus 26 to a pump 34 which is preferably located in wellbore 12 adjacent to oil producing formation 18. The water and oil mixture that passes into wellbore 12 through perforations 22 enters segment 32 of production string 28 and travels to separator apparatus 26. Separator apparatus 26 separates the water and oil mixture substantially into separated water and separated oil. The separated oil passes up upper segment 30 of production string 28 and is stored in a storage vessel 36. Alternatively, the separated oil could pass along a pipeline (not shown) or otherwise be further processed by surface equipment (also not shown.) Concurrently, water separated by separator apparatus 26 is ideally passively discharged from separator apparatus 26. That is, separator apparatus 26 preferably does not require a pump therein to expel separated water from separator apparatus 26. The discharged water flows under the force of gravity downwardly within wellbore 12 creating a column of water above packer 20.

[0021] Perforations 24 in wellbore 12 adjacent water disposal formation 16 allow the column of separated water to dissipate into water disposal formation 16.

[0022] Pump 34 may not be needed where there is sufficient reservoir pressure in oil producing formation 18 to drive the water and oil mixture to separator apparatus 26 and the separated oil to the well surface 14 for collection. Where artificial lift is needed, it is preferred, although not required in this invention, that only a single pump 34 provide the necessary driving force to lift the water and oil mixture to separator apparatus 26 and the separated oil to well surface 14. This simplifies system 12 over other systems which use a primary pump to lift an oil and water mixture to a separator apparatus and still require additional pumps to pump the separated oil to a well surface. However, while not preferred, it is still within the scope of this invention to use such an auxiliary oil pump, if necessary, to lift oil from the separator apparatus to the surface of the well while still benefiting from the use of a hydrostatic pressure head to dissipate water into a water disposal formation. In this exemplary embodiment, the primary pump system includes a pump jack 38 and a string of sucker rods 40 to drive a reciprocating pump 34. By way of example and not limitation, those skilled in the art will understand that alternative lift systems may also be used, such as an electric submersible pump or a hydraulic pump, to lift the water and oil mixture to separator apparatus 26.

[0023] Separator apparatus 26 is ideally, although it is not required to be, positioned near well surface 14. The positioning of separator apparatus 26 near well surface 14 serves two purposes. First, only a relatively short first or upper segment 30 of production string 28 need be withdrawn from wellbore 12 to gain access to separator apparatus 26. This allows for quick and inexpensive servicing if separator apparatus 26 must be taken to the surface 14 for repair or replacement. Second, by maintaining separator apparatus 26 generally near the well surface 14 of wellbore 12, the height differential between separator apparatus 26 and water disposal formation 16 is maximized. Accordingly, the hydrostatic pressure head between water leaving separator apparatus 26 and water entering disposal formation 16 is likewise maximized. While it is not preferred, separator apparatus 26 could be positioned at or above the well surface 14 with separated water again being disposed down wellbore 12 thus still enjoying the disposal advantages provided by this invention. Separated oil would again be delivered to a storage facility such as tank 36 or otherwise processed or transported away from wellbore 12.

[0024] The respective depths to the top of separator apparatus 26 and to the top of water disposal formation 16 are identified in FIG. 1 as d1, and d2. Ideally, the ratio d2/d1 of the depth of the top of water disposal formation 18 compared to the depth of the top of separator apparatus 26 is at least 2:1. More preferably, the ratio of d2/d1, is at least 10:1 and most preferably at least 50:1 or more. Another way of expressing this creation of a hydrostatic pressure head is that the depth of separator apparatus 26 should be less than 50% more preferably less than 10%, and most preferably less 5% of the depth to the top of water disposal formation 16. By way of example, and not limitation, in this exemplary first embodiment the top of separator apparatus 26 may be positioned at a depth of 50 feet and the top of water disposal formation 16 might be at 5000 feet. Consequently, a column of separated water of almost 5000 feet creates hydrostatic pressure to help dissipate separated water into water disposal formation 16.

[0025] Separator apparatus 26 used in this first exemplary embodiment may be any separator apparatus that satisfactorily separates water and oil from a water and oil mixture. For example, oil containing less than 2% water is deemed to be pipeline quality oil. Separator apparatus 26 may be chosen to meet this or other desired standards of separation.

[0026] Ideally, separator apparatus 26 is simple, economical, reliable and easily serviced. FIG. 2 illustrates a schematic cross-section of such a separator apparatus 26. Separator apparatus 26 includes a perforated steel outer cylindrical housing 42 that supports a radially disposed interior hydrophilic membrane 44. Sandwiching about membrane 44 are inner and outer protective porous layers of polypropylene, polyethylene or nylon 46 and 48. A polypropylene mesh inner layer; i.e. a pre-filter, 50 prevents the entry of particulates to membrane 44. Annular molded end caps 52 and 54 are sealed adhesively or via a hot melt process about layers 44, 46, 48 and 50. A pair of steel end caps 56 and 58 are engaged by threads with molded end caps 52 and 54. Upper and lower elastomeric O-rings 60 and 62 provide fluid sealing between molded and steel end caps 52, 54, 56 and 58.

[0027] Membrane 42 is preferably made of a modified polyacrylonitrile which is generally selectively permeable to water but much less so to oil. Other, well known hydrophilic membranes may also be used which are known for their ability to separate water and oil. Examples of such membrane materials include modified polyethersulphones, alpha alumina, and zirconia.

[0028] The mixture of water and oil is received from second segment 32 of production string 28 and introduced through bottom end caps 54 and 58 into separator apparatus 26. Membrane 44 allows water to readily permeate radially outwardly through membrane 44, exit porous housing 42 and return to wellbore 12. Meanwhile, oil cannot substantially permeate membrane 44 and becomes increasingly concentrated within separator apparatus 26 until passing out of upper end caps 52 and 56 and passing into segment 30 of production string 28. Separator apparatus 26 operates more efficiently as the relative concentration of water to which membrane 44 is exposed increases and the concentration of contacting oil decreases. As shown in FIG. 2, a fluid directing element, such as a spiral auger 64, may be attached to a portion of a sucker rod 40. Auger 64 may be releasably clipped (not shown) to a segment of sucker rod 40 or permanently affixed such as by weld joints. As sucker rod 40 rises and falls, spiral auger 64 moves relative to separator apparatus 26 and the water and oil mixture. The relative movement between the water and oil mixture and auger 64 induces a spinning or spiraling flow in the water and oil mixture passing through separator apparatus 26. Heavier water droplets are displaced radially outwardly while a core of less dense oil is formed adjacent to sucker rod 40. The movement of auger 64 relative to membrane 44 is believed to also help in limiting the accumulation of contaminants on membrane 44 and subsequent failure due to fouling. Consequently, auger 64 enhances the exposure of membrane 44 to water and the removal of water from the water and oil mixture passing by membrane 44.

[0029] It is also within the scope of this invention to use a stationary auger located within separation apparatus 26. In this case, the auger would ideally be affixed as a part of separator apparatus 26. Sucker rod 40 will be allowed to pass through the center of the stationary auger. The flow of the water and oil mixture through the stationary auger will again cause the mixture to spiral and create at least a partial separation of water and oil.

[0030] Further, the present invention also will work if no auger 64 is utilized. In fact, this is the preferred mode of operation of system 10. An advantage to using no auger 64 is that there will be less resistance to flow and head loss of fluid passing through separator apparatus 26. In this case, the length of membrane 44 may be increased to overcome the lack of turbulence or spiraling motion created in the water and oil mixture. Alternatively, a series of these membrane separators 26 may be arranged in wellbore 12 to increase the overall separation capacity of the separation system.

[0031] While in this first exemplary embodiment separator apparatus 26 is of a membrane type, those skilled in the art will appreciate that other types of separator apparatus will also work in this invention. By way of example, and not limitation, the separator apparatus may include hydrocyclones, centrifugal separators, vaned separators, etc. Also, rather than using a single stage separator, separator apparatus may include a plurality of separator devices or membranes arranged in series and/or in parallel. Additionally, the separator apparatus may be designed with radially inward flow of water rather than the radially outward flow as illustrated in FIG. 2. Furthermore, those skilled in the art will appreciate that a separator apparatus may be used with a hydrophobic membrane which permeates oil from the oil and water mixture rather than using a hydrophilic membrane that permeates water. Again, water will ideally be passively discharged into wellbore 12 while separated oil will be transported to well surface 14 for storage. Membrane 44 also may be pleated or else be formed into hollow fibers for use in a membrane separator. Such pleated or hollow fiber membranes generally provide much more surface area for exposure to the passing water and oil mixture.

[0032] FIG. 3 illustrates a second alternative separation system 110 which includes slight modifications to system 10 described above with respect to FIG. 1. Like components from system 10 have been incremented up by 100 in their reference numerals. In the event that the hydrostatic head created by the difference in height between a separator apparatus 126 and water disposal formation 116 is insufficient to cause the dissipation of separated water into a water disposal formation 116, system 110 may be used. This event may occur where the original water pressure in water disposal formation 116 is greater than that of the hydrostatic head produced by the height differential between separator apparatus 126 and water disposal formation 116. Or else, after a sufficient amount of separated water has been discharged into water disposal formation 116, the resisting water pressure in water disposal formation 116 may rise to a sufficient level wherein additional pressure may be necessary to continue to dissipate water into water disposal formation 116 from a wellbore 112.

[0033] Modified system 110 includes a second packer 172 located beneath separator apparatus 126 in wellbore 112. A pressurized water disposal chamber 174 is thus formed in wellbore 112 between a first packer 120 and a second packer 172. An auxiliary pump 176 receives separated water from a disposal conduit 180 that is in fluid communication with wellbore 112 above packer 172. Auxiliary pump 176 injects separated water into water disposal chamber 174 at a pressure sufficient to cause the dissipation of separated water into water disposal formation 116. While disposal conduit 180 is shown opening into wellbore 112, a disposal conduit could also be directly connected with separator apparatus 126 to receive separated water for disposal. Again, ideally only a single primary pump 134 is required to effect the transport of the water and oil mixture to separator apparatus 126 and separated oil to a well surface 114. Consequently, system 110 enjoys many of the advantageous features of the system 10 including the use of a hydrostatic pressure head to at least partially assist in the dissipation of waste water into water disposal formation 116. Also, system 10 may employ the simple but effective separator apparatus 26 of FIG. 2 that utilizes a hydrophilic membrane to perform separation. Again, other types of separators could also be used in this embodiment to separate water and oil.

[0034] An alternative third separation system 210, also made in accordance with the present invention, is illustrated in FIG. 4. Like components to those of system 10 and FIG. 1 are incremented by 200 in their reference numerals. In system 210, a water disposal formation 216 is located beneath an oil producing formation 218. A packer 220 separates water disposal formation 216 from oil producing formation 218. A second packer 272 is used to isolate a separator apparatus 226 from oil producing formation 218. A wellhead 225 seals off the top of wellbore 212.

[0035] Again, a separator apparatus 226 is used to separate water and oil from a water and oil mixture. Production string 228 receives a water and oil mixture from oil producing formation 218 through perforations 222 in wellbore 212. The mixture of water and oil is then delivered to separator apparatus 226. A water disposal conduit 280 allows separated water discharged from separator apparatus 226 to pass through wellbore 212 adjacent to oil producing formation 218 and reach a water disposal chamber 274 formed within wellbore 212. Separator apparatus 226 is again located at a substantial height above water disposal formation 216 to create a large hydrostatic pressure head to assist in the disposal of separated water into water disposal formation 216. While water disposal conduit 280 is shown running outside production string 228, water disposal conduit 280 can also be routed within tubing 228. n this instance, disposal conduit 280 ideally would be fluidly connected to separator apparatus 226 to receive separated water from separator apparatus 226 for disposal. If disposal formation 216 is sufficiently close to producing formation 218, the injection of separated water may also help in maintaining the fluid pressure in oil producing formation 218.

[0036] While in the foregoing specification this invention has been described in relation to certain preferred embodiments thereof, and many details have been set forth for purpose of illustration, it will be apparent to those skilled in the art that the invention is susceptible to alteration and that certain other details described herein can vary considerably without departing from the basic principles of the invention.

Claims

1. A system for separating water and oil from a water and oil mixture received from an oil well, the system comprising: a) a wellbore extending from a surface of a well to, and in fluid communication with, a water disposal formation and an oil producing formation, the oil producing formation supplying a mixture of water and oil to the wellbore; b) a separator apparatus for separating water and oil from the water and oil mixture, the separator apparatus being disposed in the wellbore at a height above the water disposal formation and above the oil producing formation; c) a first packer disposed within the wellbore which isolates the water disposal formation from the oil producing formation; and d) a production string disposed within the wellbore and having a first segment which transports the mixture from the oil producing formation to the separator apparatus; wherein the separator apparatus may separate water and oil from the mixture with the separated water being discharged from the separator apparatus and into the wellbore to create a hydrostatic column of water above the water disposal formation with the separated water being dissipated into the water disposal formation.

2. The system of claim 1 wherein the separator apparatus includes a separator membrane which substantially allows one of the oil and water to permeate through the membrane while substantially inhibiting the passage of the other of the oil and the water.

3. The system of claim 1 wherein the separator apparatus includes at least one of a hydrocyclone, a separator membrane, a centrifugal separator, and a vane separator.

4. The system of claim 1 further comprising a primary lift pump disposed within the wellbore that provides artificial lift to lift the water and oil mixture to the separator apparatus.

5. The system of claim 4 wherein the primary lift pump provides sufficient lift to the mixture to also lift the separated oil to the surface of the well without need for an additional oil lift pump.

6. The system of claim 4 wherein the primary lift pump is disposed in the wellbore adjacent to the oil producing formation.

7. The system of claim 1 further comprising a swirl inducing member to induce a swirling flow of the mixture within the separator apparatus such that heavier swirling water is placed in contact with the membrane so as to permeate out of the separator apparatus and into the column of water while the lighter oil continues to pass upwardly through the production string.

8. The system of claim 7 wherein the swirl inducing member is a generally spiral shaped vane.

9. The system of claim 1 wherein the separator apparatus includes a plurality of separation devices connected together in series within the wellbore.

10. The system of claim 1 wherein the depth to the top of the separator apparatus in the wellbore is less than 50% of the depth to the top of the water disposal formation.

11. The system of claim 1 wherein the depth to the top of the separator apparatus in the wellbore is less than 10% of the depth to the top of the water disposal formation.

12. The system of claim 1 wherein the depth to the top of the separator apparatus in the wellbore is less than 5% of the depth to the top of the water disposal formation.

13. The system of claim 1 wherein the separator apparatus is disposed beneath and generally adjacent to the surface of the well.

14. The system of claim 1 wherein the water disposal formation is located above the oil producing formation.

15. The system of claim 1 wherein the oil producing formation is located above the water disposal formation.

16. The system of claim 1 further comprising: a) a second packer disposed within the wellbore which cooperates with the first packer to create an isolated water disposal chamber which is in fluid communication with the water disposal formation; and b) an auxiliary disposal pump which pumps separated water into the water disposal chamber to increase the pressure within the water disposal chamber over and above the hydrostatic pressure head created by the column of water to enhance water disposal into the water disposal formation.

17. A method of separating water and oil from a water and oil mixture received from an oil well having a wellbore extending between, and in fluid communication with, a water disposal formation and an oil producing formation, the method comprising the steps of: receiving a water and oil mixture from an oil producing formation into a wellbore; passing the water and oil mixture up the wellbore to a separator apparatus located within the wellbore; separating the water and oil mixture into separated water and separated oil; passing the separated water to the wellbore wherein a column of water is created above the water disposal formation; and disposing of the separated water into the water disposal formation at least partially under the hydrostatic pressure created by the column of water.

18. The method of claim 17 further comprising providing additional pressure to the column of water to assist in the disposal of the separated water into the disposal formation.

19. The method of claim 18 wherein the additional pressure is provided by an auxiliary pump disposed in the wellbore.

20. The method of claim 17 wherein a primary lift pump is employed to lift the water and oil mixture to the separator apparatus.

21. The method of claim 20 wherein the primary lift pump provides sufficient lift to lift the mixture to the separator apparatus and to lift the separated oil to the surface of the well without need for an additional oil pump.

22. The method of claim 17 wherein the separator apparatus has no moving parts.

23. The method of claim 17 wherein the separator apparatus includes a membrane separator.

24. The method of claim 17 wherein the depth to the top of the separator apparatus is less than 50% of the depth to the top of the water disposal formation.

25. The method of claim 17 wherein the depth to the top of the separator apparatus is less than 10% of the depth to the top of the water disposal formation.

26. The method of claim 17 wherein the depth to the top of the separator apparatus is less than 5% of the depth of the top of the water disposal formation.

27. The method of claim 17 wherein the separator apparatus is disposed beneath and adjacent the surface of the wellbore to maximize hydrostatic head and ease of replacement of the separator apparatus from the wellbore.

28. A system for separating water and oil from a water and oil mixture received from an oil well, the system comprising: a) a wellbore extending from a surface of a well to, and in fluid communication with, a water disposal formation and an oil producing formation, the oil producing formation supplying a mixture of water and oil to the wellbore; b) a first packer disposed within the wellbore which isolates the water disposal formation from the oil producing formation; c) a separator apparatus for separating water and oil from the water and oil mixture, the separator apparatus being disposed in the wellbore at a height above the water disposal formation and above the oil producing formation and including a membrane separator; d) a production string disposed within the wellbore and having a first segment which transports the mixture from the oil producing formation to the separator apparatus and a second segment which transports separated oil from the separator apparatus to the surface of the well; e) a lift pump to lift the mixture of water and oil to the separator apparatus and the separated oil to the surface of the well; and f)an auxiliary pump to provide additional pressure to the column of water to assist in the disposal of water into the water disposal formation.