Patent Publication Number: US-2011056698-A1

Title: Fluid separation system for hydrocarbon wells

Description:
The instant application is related to and claims priority to co-pending provisional application 61/274,521, filed Aug. 18, 2009, entitled Fluid Separation System for Hydrocarbon Wells, inventors Clint J. Talbot and Raymond Arreola. The above referenced co-pending application Ser. No. 61/274,521 is herein and hereby incorporated by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to a downhole heavy fluid exhaust system for a pumped hydrocarbon well (herein “oil” well) and in particular relates to relatively slowly producing wells with a downhole pump and sucker rod. 
     BACKGROUND OF THE INVENTION 
     In a producing “oil” well a production zone is typically packed off, top and bottom. In many wells, especially older wells, the formation pressure at the production zone is less than the head pressure of the formation fluid in the production tubing, requiring the formation fluid to be lifted, or pumped, to the surface. Downhole jack pumps with a pump piston, a traveling valve, a stationary valve and a sucker rod are traditionally used to lift formation fluid in the production tubing to the surface, as well as to draw formation fluid into the production tubing and into the well from perforations in a well casing. 
     Older wells producing with a downhole jack pump typically produce both oil and water at a relatively slow rate. Producing the water to the surface is inefficient. Further, water produced at the surface must be safely disposed. Older wells, using a jack pump with a relatively slow rate of production, could operate to an advantage by reducing or eliminating the water produced to the surface. 
     The instant invention relates to a surface-adjustable, head pressure triggered, downhole water exhaust valve. In preferred embodiments a surface-adjustable, mechanical downhole valve, together with its associated tool, is attached to the jack pump and triggered to open and close in order to produce essentially oil at the surface. Oil is produced from a combined oil and water producing well by means of exhausting the heavier water downhole, periodically or relatively continously. The downhole exhaust valve and associated tool structure, in preferred embodiments, exhausts produced and settled water from within the production tubing into a formation region below a lower production packer. 
     In preferred embodiments the valve attaches to the bottom of a downhole jack pump. The downhole pump includes a sucker rod extending from the surface and attached to a lifting piston in a cylinder in the bottom of the production tubing at the producing formation level, as is known in the art. Fluid produced through perforations in the casing at the producing level enters the bottom of the production tubing and pump cylinder through a stationary check valve. During a lifting cycle the piston attached to the bottom of the sucker rod lifts production fluid up the tubing and out at the surface while it draws in production fluid through the stationary check valve below the piston. During the downward cycle of the piston the stationary check valve closes, holding the column of fluid in the pump cylinder and production tubing while a traveling valve in the piston opens, permitting the piston to descend. The piston typically rises and descends to its original downhole position with minimal disturbance of the formation fluid in the production tubing. 
     The production tubing itself, including extensions thereto and chambers associated therewith, function as a settling tank in a well producing slowly enough. The oil typically weighs 80% to 90% of the water. Given adequate settling time vis-à-vis lifting time, gravity tends to raise the oil portion of the produced formation fluid to the top of the production tubing and to settle the water portion of the produced formation fluid to the bottom. The pump strokes of a downhole jack pump do not unduly disturb the settling within the production tubing. A hypothetical interface in the production tubing can be viewed as separating an upper predominantly oil portion and a lower predominantly water portion. 
     The instant invention places a surface-adjustable exhaust valve downhole in the bottom of the well, preferably attached to and below the jack pump, sensitive to the head pressure of the production tubing fluid and in fluid communication with the production tubing through a secondary chamber system. At a certain adjusted point of the valve targeting and triggering system, such as a spring biasing system, head pressure of the fluid in the production tubing opens the valve and discharges water (that has settled to the bottom portion of the production tubing, including associated chambers.) Preferably the water is discharged lower into the formation, below the production zone, into a low pressure region. Discharging continues until the fluid head pressure in the production tubing falls below the targeted valve. A certain amount of hysteresis may occur and may be beneficial. The discharging could be periodic or relatively continuous. 
     In accordance with the instant system, the downhole pump should produce largely oil from the top of the production tubing, if run at an appropriate rate to permit the settling of water, while the surface-adjustable targeting, or biasing force, on the exhaust valve permits head pressure of the production tubing to exhaust settled water. Again, the exhaust valve could be designed and structured such that it functions either continuously or intermittently, and could intentionally include hystersis. 
     It is significant that the exhaust valve is adjustable from or at the surface in order to fine tune the balance in movement between the settling and exhausting water on the one hand and the raised and produced oil on the other hand. Basically the exhaust valve and jack pump together maintain a water/oil separation level or interface within the production tubing. Such balance is achieved by the intermittent or continuous flushing of the heavy fluid, or water, from the bottom of the production tubing into the formation, preferably below a lower production packer, while essentially lighter production fluid, or oil is pumped out at the surface. The flushing below complements the production of fluid at the surface. Again, the flushing and production rate should be coordinated with, and take into account, the production capacity of the well and the settling/rising rate of the formation fluids in the production tubing. 
     A preferred embodiment of the instant invention and associated tool utilizes a second chamber system associated with, and in fluid communication with, the production tubing, located downhole in the production zone region between upper and lower packers, around the pump. The exhaust valve preferably operates out of the secondary chamber. A separator housing attached to and surrounding a portion of the production tubing and pump, inside the well casing, creates a second annular chamber for production fluid, preferably in fluid communication with the production tubing toward the top of the packed off production zone. The weight and head pressure of the production fluid in the production tubing is transmitted to the second chamber. The exhaust valve is set to be triggered by the head pressure of the production fluid in the chamber and production tubing. In a preferred embodiment the valve senses the head pressure within the second annular chamber. Knowing the depth of the well, the anticipated water cut of the formation fluid and anticipated weight of the oil, the anticipated head pressure range at the valve can be roughly estimated beforehand. 
     The invention utilizes production tubing head pressure to provide the motive force for exhausting the settled water in the secondary chamber when the exhaust valve is open. When sufficient water has been exhausted, such that the head pressure falls below the adjustable target point, the water exhaust valve closes by virtue of a biasing force. By an alternate design the valve stays marginally open to maintain a targeted head pressure. 
     In a first preferred embodiment the valve is spring biased. Although the resistance of heavy duty industrial springs, appropriate for the instant invention, can exhibit a fair range of variance from one spring to the next, a single spring tends to perform consistently over time, within a relatively small range of variance with respect to itself. Thus, a given spring, once adjusted to yield a satisfactory result in a well, should tend to maintain that result with an acceptable level of variation. 
     SUMMARY OF THE INVENTION 
     In one embodiment of the invention, a perforated well casing is packed off into a production zone. Production tubing extends between the packers and includes a second chamber, both chambers affected by the tendency of the oil and water to separate in the production tubing and both affected by the production tubing head pressure. The primary production tubing chamber carries the pump piston that draws in fresh fluid from the formation into the zone and that lifts the fluid to the surface. The secondary chamber carries the surface-adjustable exhaust valve that exhausts heavier settled fluid into a region below a lower packer. The surface-adjustable valve in the second chamber is sensitive to the weight or head pressure of the fluid in the production tubing, and a target opening range of the valve, or biasing range, takes into account the height of the well, the anticipated ratio of weight of oil to weight of water and expected water cut of the formation fluid. The surface adjustment of the targeting or biasing sets the valve to open above a given head pressure. The valve tends to return well head pressure to at or below that value by releasing heavy fluid out through a tail pipe into the formation below the lower packer. Assuming pumping rates and exhaust rates are properly managed, a jack pump can produce essentially oil while the exhaust valve exhausts essentially water. 
     Thus, a surface-adjustable heavy fluid exhaust valve is provided downhole, adjustably targeted or biased from the surface to open at a point (as between approximately 80% to 100% water head pressure in the production tubing) such that essentially oil is produced at the surface, without any significant loss of oil by inadvertent exhaust. The valve is preferably attached directly or indirectly to a downhole jack pump. The bias of the valve is adjustable from the surface by manipulation of the jack pump at the surface. One exhaust valve side is in fluid communication with the production tubing fluid and head pressure. A second valve side is in fluid communication with the formation outside of the producing region. A surface-adjustable element, such as a biasing spring, determines when the valve opens or triggers. 
     The instant inventive exhaust valve and system preferably includes a tool that attaches to the end of a traditional downhole jack pump and production tubing. The tool preferably includes not only an adjustable downhole valve and a second chamber but also a cross-over portion to allow formation fluid inside the perforated casing to enter the production tubing through the stationary check valve while at the same time permitting fluid in the second chamber to flow downward through vertical channels in the cross-over portion to the downhole exhaust valve. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A better understanding of the present invention can be obtained when the following detailed description of the preferred embodiments are considered in conjunction with the following drawings, in which: 
         FIG. 1  illustrates a preferred embodiment of a tool embodying the instant invention. 
         FIGS. 2 ,  3  and  4  illustrate three details of  FIG. 1 . 
         FIGS. 5 through 9  illustrate the tool of  FIG. 1  in colored drawings to distinguish its parts more specifically. 
         FIG. 10  illustrates the tool with a breakout into two section details, giving parts numbers. 
       Subsequent  FIGS. 11-32  are parts drawings corresponding to  FIG. 10 . 
         FIGS. 33A and 33B , from Wikepedia, illustrate the workings of a basic pump jack. 
         FIGS. 34A-E  illustrate in photographs portions of a pump jack, useful for providing a surface-adjustable feature. The drawings are primarily illustrative. It would be understood that structure may have been simplified and details omitted in order to convey certain aspects of the invention. Scale may be sacrificed to clarity. 
     
    
    
     The details of the typical jack pump sucker rod SR and pump PP in  FIGS. 2 and 3  for instance, are not illustrated.  FIGS. 33A and 33B  with drawings, photos and text illustrate the general principles of the pump jack. The pump jack has a piston/traveling valve that moves within a pump cylinder. The piston/traveling valve is connected by the sucker rod through the production tubing to the surface and the pump motor mechanism at the surface. As illustrated and described in  FIG. 33A  and text in  33 B a jack pump lifts fluid up the production tubing on its upstroke while it draws in fluid below the piston into the pump cylinder on the upstroke. On the upstroke the traveling valve is closed and the lower standing valve is open. On the downstroke the traveling valve is open. The pump piston moves through the fluid in the pump cylinder to its lower position. The standing valve is closed such that the fluid in the pump cylinder remains in the pump cylinder during the downstroke of the jack pump. 
     There is another aspect of typical jack pumps, not illustrated in  FIGS. 33A and 33B , significant for preferred embodiments of the invention. This aspect is illustrated in the photographs of  FIGS. 34A-E . In general operation, production tubing is set in the well. The jack pump is then lowered into the production tubing. The pump comprises primarily a sucker rod and a pump cylinder with piston and traveling valve. The pump cylinder also contains a stationary valve. Within the pump cylinder attached to the sucker rod, is the pump piston and the traveling valve. Provision is typically made to seat a jack pump cylinder in the production tubing. For that purpose the typical jack pump is connected to a lower extension that can screw into a seating nipple attached to a portion of the production tubing. By screwing in the pump cylinder extension to a nipple seat in a portion of the production tubing, the jack pump is seated within the well for operations.  FIGS. 34A-E  illustrate a means for screwing an extension attached to a lower portion of the pump cylinder into a seating nipple. In  FIGS. 34A-E  the left side of the figure is up and the right side of the figure is down. In  FIG. 34A  the pipe section of smaller diameter is a portion of the sucker rod. It carries a segment of larger diameter, the diameter of the pump cylinder, having lugs. One lug is illustrated in  FIG. 34A .  FIG. 34B  is rotated approximately 90 degrees to illustrate two lugs on the segment carried by the sucker rod. When the sucker rod is extended to its lowest position within the pump cylinder (the pump cylinder, being the portion of the larger diameter illustrated on the right of the drawing  34 A,) the lug on the sucker rod seats within a notch at the top of the pump cylinder.  FIG. 34C  shows the sucker rod extended to its lowest position such that the lug carried by the sucker rod is seated within the notch of the cylinder of the pump. As seated, the sucker rod can be rotated at the surface and the rotation is transmitted through the lug and notch to the cylinder of the pump, and to its extension therebelow. By rotating the sucker rod the pump cylinder extension can be screwed into the seating nipple attached to the production tubing. 
     The above feature of jack pumps is utilized in a preferred embodiment of the instant invention. 
     As illustrated in  FIG. 3  the instant invention replaces the typical extension from the bottom of the cylinder of the jack pump (or the pump jack) with extension S 1 , passing through the crossover fluid communication unit and further attached to extension S 2 . Rotating the sucker rod rotates the pump cylinder PP, rotates extension S 1 , and rotates extension S 2 . Rotating extension S 2  rotates and screws further extension S 3  into nonrotating portion S 4 , thereby moving S 4  up and down within its chamber. Rotating portion S 4  draws up portion S 5  and thereby changes the compressive force of spring SP on the valve. 
     Element S 1  and its interconnected pieces also serve to seat the jack pump with respect to the lower production tubing. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The theory of the system is to permit the production tubing to function as a settling tank, permitting, with proper timing, producing lighter fluids off the top (oil) while exhausting, in a coordinated fashion, heavier fluids (water) off the bottom, the producing being coordinated with or taking into account the settling/rising rates of the formation fluids and the producing rate of the well. The weight of the fluid in the production tubing provides the motive force for the exhaust and triggers the opening of the exhaust valve. A key to the invention is the surface-adjustable feature of the exhaust valve which coordinates exhaust of the heavier settled fluid with the production of the lighter rising fluid and with the rising/settling rates of the formation fluid. 
       FIG. 1  illustrates casing C having perforations P and tool T divided into three sections, section B, section C and section D. Section B is the subject of  FIG. 2 . 
     Section B illustrates casing C with perforations P. Inside of casing C is production string or production tubing PT packed off against the casing by upper packer UP. The sucker rod SR passes through the production tubing and pump PP resides within the lower portion of the production tubing. 
     The instant invention adds a separator housing SH sealed against production tubing PT toward the upper portion of production zone PZ defined within the perforated casing and between the upper and lower packers UP and LP. The separator housing SH together with the production tubing PT defines a secondary, in part annular chamber SC. Chamber SC is in fluid communication with the production tubing chamber defined by PT, through orifices O. 
     As illustrated by  FIG. 3  fluid enters production zone PZ through perforations P and casing C. The fluid is drawn in by action of the pump PP. Fluid from the production zone enters the production tubing PT through oval shaped inlet ports IP in communication with the production zone, the ports provided by a section CR of the separator housing SH of the instant tool. This section of the separator housing SH is referred to as crossover CR. Fluid in upper portions of the annular secondary chamber SC, between the separator housing SH and the production tubing PT, flows downward through vertical ports VP in the crossover section CR of the separator housing SH. Hence the crossover section provides both for vertical fluid communication for fluids in the secondary chamber as well as for horizontal communication for fluid from the production zone into the central pump chamber in the bottom of production tubing PT. 
     Two segments of the instant tool, referred to as S 1  and S 2 , attach to a lower portion of the cylinder of pump PP. These two segments S 1  and S 2  are adapted to rotate with pump PP cylinder and with interlockable sucker rod SR within outer stationary portions of the instant tool T.  FIG. 4  shows a third segment S 3  attached to S 2  and also adapted to rotate within tool T. As S 3  rotates it progressively screws into nonrotating tool section S 4  thereby pulling the lower section of the tool up as section S 3  rotates. Sections S 1 , S 2  and S 3  are caused to rotate by rotating the sucker rod at the surface, which in a preferred embodiment can interlock with the pump cylinder. The raising of section S 4  and the lower portions of the exhaust valve connected thereto tends to release the compression of spring SP within its spring chamber thereby reducing the resisting pressure of plug PG and tip PT within plug seat PO to production tubing head pressure. Plug tip PT is sensitive to the pressure of the fluid in the production tubing and the secondary chamber. When the pressure of the fluid in the production tubing and the secondary chamber overcomes the resistance of spring SP as adjusted, plug tip PT will move out of plug seat PO permitting fluid in secondary chamber SC to flow down past the spring chamber and out of tailpipe TP through lower packer LP. 
       FIGS. 5 through 9  offer colored illustrations of the instant tool and of the tool as it resides within the casing. (Note: in  FIG. 9 , spring SP should be drawn to extend upward against the upper barrier in the spring chamber.) 
       FIG. 10  and the parts drawings thereafter illustrate in greater detail portions of the instant preferred embodiment tool. Detail B of  FIG. 10  illustrates the crossover tool where fluid in the secondary chamber defined by the separator housing, only partially shown, can pass vertically down the tool while fluid from the production zone outside the separator housing can flow into the center of the tool through the horizontal oval ports. 
     In operation, a relatively slowly producing well is identified where the rate of production is such that the water has time to significantly settle in the production tubing and the oil to significantly rise. 
     In a preferred embodiment, a tool incorporating the instant invention is attached at the end of a pump jack and the tool and pump jack is inserted into the production tubing in the well and located opposite a producing strata with perforated casing. The pump and the tool inserted into the production tubing is packed off with upper and lower packers, creating a production zone inside the casing. 
     The bias of the valve, and in the case of a preferred embodiment, the spring of the valve, is initially set on a high side. The weight of the fluid in production tubing and secondary chamber can be roughly estimated based on the depth of the production zone, the weight of the formation fluids, in particular the water and the oil, and the water cut of formation fluids in the hole. A spring is selected for the valve that corresponds roughly to the appropriate levels of resistance. In a preferred embodiment the spring is further preset by the capacity to adjust a lower portion of the spring chamber. The upper portion of the spring chamber is preferably initially set at or close to a maximal resistance level. The initial operational intent is that the valve does not exhaust until the production tubing and secondary chamber contains a significant portion of water, significant in relation to the anticipated or expected downhole water cut. 
     After production is begun the sucker rod and lower extensions of the sucker rod and pump cylinder connected to the tool can be rotated when the sucker rod is in a lower position. Such rotation, through the action of fittings, raises an upper limit to the spring chamber, thereby reducing the biasing force of the spring and reducing the level of pressure required for the fluid in the production tubing to force the valve from the valve seat. Gradually the spring bias resistance is reduced by operation at the surface, thereby gradually exhausting greater amounts of water through the valve until essentially only oil is produced at the surface. 
     The pump rate of the pump lifting the oil to the surface may also be regulated or coordinated such that a hypothetical oil/water interfere remains within the production tubing. 
     The instant invention could be designed to work with pumps other than a jack pump. The biasing means of the valve could include biasing means other than a spring. In particular a pilot valve system might be used to control the valve in order to increase sensitivity and accuracy. 
     The foregoing description of preferred embodiments of the invention is presented for purposes of illustration and description, and is not intended to be exhaustive or to limit the invention to the precise form or embodiment disclosed. The description was selected to best explain the principles of the invention and their practical application to enable others skilled in the art to best utilize the invention in various embodiments. Various modifications as are best suited to the particular use are contemplated. It is intended that the scope of the invention is not to be limited by the specification, but to be defined by the claims set forth below. Since the foregoing disclosure and description of the invention are illustrative and explanatory thereof, various changes in the size, shape, and materials, as well as in the details of the illustrated device may be made without departing from the spirit of the invention. The invention is claimed using terminology that depends upon a historic presumption that recitation of a single element covers one or more, and recitation of two elements covers two or more, and the like. Also, the drawings and illustration herein have not necessarily been produced to scale.