Patent Application
20060037746
Oil well production, and more particularly to a downhole oil and water separator and method.
In oil well production operations, relatively large quantities of water are frequently produced along with the oil. In some oil wells, water and other by-products can amount to as much as eighty to ninety percent of the total production yield. This is particularly true during the later stages of production.
Various methods have been employed for separating the oil from the water. For example, oil and water are typically pumped or otherwise flowed together to the surface where they are treated to separate the oil from the water. The water, after having been pumped to the well surface and separated, is disposed of by removal from the site or by pumping back into the well for injection into a disposal layer.
Downhole separation has also been used to separate the oil and water produced by a well. For example, hydroclones, dynamic mechanical systems that use centralized forces to separate fluids, and combinations of mechanical pumps and gravity separation have been used for achieving separation of production fluids into water and oil components. Hydrophilic and other semi-permeable membranes have been used in connection with submersible pumps for downhole separation.
Oil and water are separated downhole using a water-selective membrane. The separated water may be disposed of downhole and the oil produced to the surface.
In a particular embodiment, the downhole oil and water separator includes a plurality of perforated collector tubes disposed laterally in the production flow path. In this embodiment, the collector tubes may overlap or criss-cross to form a serpentine or other high contact area flowpath. In another embodiment, the water-selective membrane may be included in a filter element disposed in the production flowpath at the level of the disposal zone. In these and/or other embodiments, the production flowpath may be filtered without downhole mechanical pumping.
Technical advantages of one or more embodiments of the downhole oil and water separator and method include providing an improved method and system for separating oil and water downhole within a wellbore. For example, water may be separated from the oil in the production flowpath and injected into a disposal zone without use of mechanical pumping. In particular, water may be removed from the production flowpath through the water-selective membrane at the level of or otherwise in communication with a disposal zone. Accordingly, equipment and production costs are reduced.
Another technical advantage of one or more embodiments of the downhole oil and water separator includes providing a water-selective filter with increased efficacy. In particular, the separator may include a plurality of perforated collector tubes disposed laterally in the production flowpath or otherwise to form a serpentine flowpath or otherwise increase surface contact area of the filter for increased water removal. Accordingly, the concentration of water in the produced fluids at the surface is reduced.
These technical advantages may be present in none, some or all embodiments of the downhole oil and water separator and method. In addition, other technical advantages will be readily apparent based on the following figures, description and claims.
Like reference symbols in the various drawings indicate like elements.
Wellbore 20 is cased with casing 30 which may be cemented in place at the bottom of wellbore 20. Perforations 32 may be formed in the casing 30 at the level of production zone 24. Similarly, perforations 34 may be formed in the casing 30 at the level of the disposal zone 26. The perforations 32 in the production zone 24 allow formation fluids 36 including oil and water to enter into the interior of the casing 30 for treatment and production. Perforations 34 in the disposal zone permit water 38 separated from the formation fluid 36 to be discharged, disposed of or otherwise injected into disposal zone 26. The perforations 32 and 34 may be formed by conventional or other suitable techniques. In another embodiment, the production tubing may have an open bottom in place of or in addition to perforations.
A production tubing 40 extends in the wellbore 20 from a surface wellhead 42 to the production zone 24. An annulus 46 formed between the casing 30 and the production tubing 40 is sealed off by packers 44 at or near the upper and lower boundaries of the disposal zone 26. The packers 44 may be conventional production or other suitable packers positioned to isolate in the annulus 46 at production zone 24 from the annulus 46 at the disposal zone 26. The production tubing 40 includes perforations 48 to allow formation fluids 36 to enter into the interior of the tubing 40. The production tubing 40 defines, in the illustrated embodiment, a production flowpath 50 from the production zone 24 to the wellhead 42. Formation fluids 36 may otherwise enter into the production tubing 40.
The production tubing 40 includes a downhole oil and water separator 52 at, in one embodiment, the level of the disposal zone 26. The oil and water separator 52 may be otherwise suitably positioned in the flowpath 50. For example, the oil and water separator 52 may be disposed adjacent to the production zone 24. The downhole oil and water separator 52 is operable to separate at least some water 38 from oil in the production flowpath 50. The separated water 38 may include a minority oil phase. Thus, the downhole oil and water separator 52 may partially separate, substantially separate or completely separate the oil and water in the production flowpath 50. As used herein, water 38 may include water as well as associated by-products in the formation fluid 50. Oil may be any suitable hydrocarbon or other petroleum product.
The downhole oil and water separator 52 includes a filter element 54. In one embodiment, the filter element 54 may have a height substantially equal to the height of the disposal zone 26. In other embodiments, the filter element 54 may have a height greater than, substantially greater than, less than, or substantially less than that of the disposal zone 26. The filter element 54 may be cylindrically shaped and in direct fluid communication with the disposal zone 26 via annulus 46.
The filter element 54 comprises a water-selective membrane. The water-selective membrane may be a hydrophilic membrane or other material that has a strong affinity for water. Such materials may be sized to pass smaller water molecules while blocking larger hydrocarbons. Other materials may include expanded polytetra-fluoro-ethylene (EPTFE) and non-expanded PTFE.
One or more chokes 60 may be provided in the production tubing 40 to control differential pressure in the production tubing 40 between the levels of the production zone 24 and the disposal zone 26 and/or between the production tubing 40 and the disposal zone 26. Thus, for example, formation fluids 36 in the production tubing 40 at the level of the disposal zone 26 may have a pressure that is 3 to 5 pounds per square inch (psi) higher than that of the disposal zone 26 to ensure the flow of water 38 is into the disposal zone 26. The differential pressure may be suitably varied. In some embodiments, the chokes 60 may be omitted. The choke may be any suitable pressure regulation or control system.
In operation, formation fluids 36 including oil and water enter into the production flowpath 50 via perforations 32 and 48 in the casing 30 and production tubing 40, respectively. As previously discussed, formation fluids 36 may enter the production flow path 50 via an open bottom or otherwise. Formation fluids 36 flow up the production tubing 40 to the wellhead 42 based on reservoir pressure. In a particular embodiment, a submersible or other pump may be used for lift. As the production fluids 36 are conveyed through the downhole oil and water separator 52, water 38 is removed via the water-selective membrane of the filter element 54 to form separate water and oil streams. The water stream may have a minority oil phase and/or be substantially or completely water. Similarly, the oil stream may have a minority water phase and/or be substantially or completely oil. The water stream 38 is conveyed through perforations 34 in the production casing 30 or other suitable openings to the disposal zone 26. Accordingly, the concentration of oil in the formation fluids 36 reaching the wellhead 42 is higher than that originally received from the production zone 24.
FIGS. 2A-B illustrate additional embodiments of the oil and water separator 52. In these embodiments, the filter element 52 comprises a plurality of perforated collector tubes with the water-selective membrane covering the perforations. The collector tubes may be any suitable piping or channel operable to convey water 38 to the disposal zone 26. Water 38 is conveyed to the disposal zone 26 when it carried to or toward the zone 26. The perforations may be any openings suitable to receive water 38 from the production flowpath 50. The membrane may be disposed outwardly or inwardly of the collector tubes, or otherwise to selectively pass water 38 from the formation fluid 36 into and/or along the collector tubes. In particular,
Referring to
The collector tubes 80 form a series of concentric annular flowpaths 84 through the downhole oil and water separator 52. The annular flowpaths 84 provide an increased surface contact area between the formation fluids 36 flowing in the production flowpaths 50 and the water-selective membrane 81 of the filter element 54. Accordingly, a greater amount of water 38 may be removed from the production flowpath 50 to minimize water produced at the surface that must be reinjected.
Referring to
The serpentine flowpath 50 increases the surface area of the filter element 54 exposed to the production flowpath 50 and enhances water separation from formation fluids 36 produced to the wellhead 42. In this embodiment, the filter element 54 may have tens, hundreds or more collector tubes 90 each extending two-thirds or more of the way across the diameter of the production tubing 40 and spaced within a diameter of each other. In a particular embodiment, the tube of this or other embodiments may be spaced such that fluid disturbances created by vortex shedding interact with neighboring tubes. Also, in this embodiment, the collection tubes 90 may have a width extending from one side to the other side of the production tubing 40. In other embodiments, a plurality of round, oval or other suitable collector tubes 90 may be disposed at each level. Collector tubes 90 may be otherwise suitably configured and/or disposed in the production flowpath 50 for separating water 38 from formation fluids 36.
Referring to
The downhole oil and water separator 152 is retrievably disposed in the production tubing 140. In one embodiment, the production tubing 140 includes a landing nipple with a lock mandrel connector 156 to allow the downhole oil and water separator 152 to be periodically removed and replaced. In this embodiment, a set of seals 158 may be disposed between the filter element 154 and the production casing 140. A choke 160 may be disposed at the top of the oil and water separator 152 to maintain a differential pressure between formation fluids 136 in the filter element 154 and the water or other fluid in the disposal zone 126.
The filter element 154 comprises a filter stack including criss-crossing collector tubes 162. The collector tubes 162 may each be perforated and extended laterally across the filter element 154. The collector tubes 162 may be covered internally, externally or otherwise with the water-selective membrane to filter out water 138 from formation fluids 136 flowing through the filter element 154.
In operation, formation fluids 136 flow at pressure from the production zone 124 through perforations 132 and into the production tubing 140. As the formation fluids 136 travel through the filter element 154, water 138 is separated out through the water-selective membrane and communicated by the collector tubes 162 through perforations 164 in the production tubing 140 and perforations 134 in the casing 130 to disposal zone 126. At the outlet of the filter element 154, the formation fluids 136 include a higher concentration of oil than the fluids received from the production zone 124. In a particular embodiment, all, substantially all, or the majority of the water 138 may be removed from the formation fluids 136 by action of the downhole oil and water separator 152. In another embodiment, a majority, but a reduced amount of the formation fluids 136 may comprise water after filtering.
Although not illustrated in
A pump may be used to control the flow rate of fluid in the downhole oil and water separator to continually clean the membrane. For example, at flow rate of 10-30 feet per second, oil and solids that otherwise accumulate may be scraped off, eroded or otherwise removed from the membrane to leave it exposed. In another embodiment, a pump may be used to inject separated water 138 into the disposal zone 126. For example, in an embodiment in which the disposal zone 126 is located below the level of the producing zone 124, the downhole oil and water separator 152 may be positioned at the level of the production zone 124 and separated water 138 may flow by gravity downward to a pump coupled to an end of the oil and water separator 152. The pump may force or otherwise inject the water 138 into the disposal zone 126. As previously described, a mechanical pump may be completely omitted and flow otherwise controlled.
FIGS. 4A-B illustrate details of one embodiment of the filter stack of
Referring to
Referring to
Referring to
The downhole oil and water separator 252 may be a multi-stage separator and may in one embodiment include a first stage separator 256 and a second stage separator 258. Additional stages may also be included. The first stage separator 256 may be a gravity oil and water separator at a level of the production zone 224. The first stage gravity oil and water separator may be used, for example, in wells with low overall flow rates. In other embodiments, a hydrocyclone or orbital separator may be used at the level of the production zone 224 or elsewhere. The gravity oil and water separator 256 may have an inlet 260, an oil outlet 262 and a water outlet 264. The oil outlet 262 of the gravity oil and water separator 256 may be connected to the production tubing 240 for production of the egress oil stream to the wellhead 242. A pump 270 may be disposed at the oil outlet 262 of the gravity separator 256 to assist in production of the oil stream to the surface 222.
The water outlet 264 from the gravity oil and water separator 256 may feed into the second stage separator 258. In this embodiment, the second stage separator 258 includes a filter element 272 with a water-selective membrane. A pump 274 may be disposed at the water outlet 264 to pressurize water flowing into the second stage separator 258.
In the second stage separator 258, water 238 passing through the water-selective membrane is injected into the disposal zone 226. Oil and/or water not passing through the water-selective membrane may be recirculated through a recirculation passage 276 back to the first stage separator 256. In this embodiment, the water-selective membrane in the second stage separator 258 may be used to clean-up water output from the first stage separator 256. The first stage and/or second stage separators 256 and 258 may be configured in any suitable manner. For example, the disposal zone 226 could, as previously described, be below the level of the production zone 224. In any event, the water-side outlet of the first stage separator 256 is circulated past the water-selective membrane, which allows water to pass, and re-circulates the remaining oil-enriched water through the first stage separator 256. The use of the first and second stage separators 256 and 258 may reduce the amount of water produced to the surface 222 from the single-stage separator embodiment.
A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, a sump may be formed beneath a production zone such that solid debris falling out from the filtering process will not build up and interfere with production. Accordingly, other embodiments are within the scope of the following claims.
