Abstract:
Apparatus and methods for well pumping utilizing a submersible system comprising a pump body having a pump chamber and a hydraulic chamber. A diaphragm is disposed within the pump chamber and divides the pump chamber into a pumped fluid chamber and a hydraulic fluid chamber. A piston is disposed within the hydraulic chamber such that movement of the piston within the hydraulic chamber creates a differential pressure across the diaphragm. A coupling is connected to the piston and operable to connect the piston to a rod extending from the top of the well.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     Not Applicable.  
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     Not Applicable.  
       BACKGROUND  
       [0003]     The present invention relates generally to methods and apparatus for submersible pumping systems. More particularly, the present invention relates to methods and apparatus for submersible pumps used in artificial lift systems for producing low flow rate oil, gas and coal bed methane wells.  
         [0004]     Hydrocarbons, and other fluids, are often contained within subterranean formations at elevated pressures. Wells drilled into these formations allow the elevated pressure within the formation to force the fluids to the surface. However, in low pressure formations, or when the formation pressure has diminished, the formation pressure may be insufficient to force the fluids to the surface. In these cases, a pump can be installed to provide the required pressure to produce the fluids.  
         [0005]     The volume of well fluids produced from a low pressure well is often limited, thus limiting the potential income generated by the well. For wells that require pumping systems, the installation and operating costs of these systems often determine whether a pumping system is installed to enable production or the well is abandoned. Among the more significant costs associated with pumping systems are those for installing, maintaining, and powering the system. Reducing these costs may allow more wells to be produced economically and increase the efficiency of wells already having pumping systems.  
         [0006]     The operation of a downhole pumping system depends on providing energy, which is converted to hydraulic power that lifts fluid from the well. Thus, the transmission of hydraulic power between the surface and a downhole pump is one the key elements that determines the efficiency, size, and operating characteristics of a downhole pumping system. For example, a rod pump, which is the dominate means of pumping fluids from oil and gas wells, uses a reciprocating steel rod as the means to transmit energy from the surface to the downhole pump. Rod pumps, although plentiful, suffer serious limitations, especially under harsh conditions. Most of the problems stem from wear in the pump due to the interaction of the pumped fluid with the pressure generating (piston-cylinder) portions of the pump.  
         [0007]     There remains a need to develop lower cost, more efficient methods and apparatus for pumping fluids from a low pressure wellbore that overcome some of the foregoing difficulties while providing more advantageous overall results.  
       SUMMARY OF THE PREFERRED EMBODIMENTS  
       [0008]     The embodiments of the present invention are directed toward apparatus and methods for well pumping utilizing a submersible system comprising a pump body having a pump chamber and a hydraulic chamber. A diaphragm is disposed within the pump chamber and divides the pump chamber into a pumped fluid chamber and a hydraulic fluid chamber. A piston is disposed within the hydraulic chamber such that movement of the piston within the hydraulic chamber creates a differential pressure across the diaphragm. A coupling is connected to the piston and operable to connect the piston to a rod extending from the top of the well.  
         [0009]     In certain embodiments, a well pumping system comprises a rod extending into a tubing string disposed in a well. A submersible pump is disposed in the well and coupled to the rod. The submersible pump comprises a pump body having a pump chamber and a hydraulic chamber, where a diaphragm is disposed within the pump chamber and divides the pump chamber into a pumped fluid chamber and a hydraulic fluid chamber. A piston is disposed within the hydraulic chamber such that movement of the piston within the hydraulic chamber creates a differential pressure across the diaphragm. An inlet valve selectively controls the flow of fluid from the well into the pumped fluid chamber and an outlet valve selectively controls the flow of fluid from the pumped fluid chamber into an annular region between said rod and the tubing string.  
         [0010]     In some embodiments, a method for installing an operating a well pumping system comprising connecting a submersible pump to a rod and extending the rod into a tubing string disposed in a well. The submersible pump is connected to the tubing string. The pump is operated by actuating the rod so as to reciprocate a piston that is disposed within a hydraulic chamber of the submersible pump. Fluid pressure is transferred from the hydraulic chamber to a pump chamber of the submersible pump, wherein a diaphragm divides the pump chamber into a pumped fluid chamber and a hydraulic fluid chamber so that as pressure within the hydraulic fluid chamber decreases, fluid is pulled into the pumped fluid chamber from the well and as pressure within the hydraulic fluid chamber increases fluid is moved from the pumped fluid chamber into an annular area between the rod and the tubing string.  
         [0011]     Thus, the present invention comprises a combination of features and advantages that enable it to overcome various problems of prior devices. The various characteristics described above, as well as other features, will be readily apparent to those skilled in the art upon reading the following detailed description of the preferred embodiments of the invention, and by referring to the accompanying drawings.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     For a more detailed description of the preferred embodiment of the present invention, reference will now be made to the accompanying drawings, wherein:  
         [0013]      FIG. 1  is a schematic view of one embodiment of a reciprocating rod-driven submersible pumping system utilizing a boot seal;  
         [0014]      FIG. 2  is a schematic view of a submersible pump utilizing a bottom hold down system;  
         [0015]      FIG. 3  is a schematic view of a submersible pump utilizing a top hold down system;  
         [0016]      FIG. 4  is a schematic view of a submersible pump mounted on production tubing  
         [0017]      FIG. 5  is a schematic view of one embodiment of a reciprocating rod-driven submersible pumping system utilizing wiper seals; and  
         [0018]      FIG. 6  is a schematic view of one embodiment of a rotating rod-driven submersible pumping system. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]      FIG. 1  shows a submersible pump  10  coupled to a reciprocating rod  12  via connecting rod  14  and couplings  16 . Pump  10  comprises body  18 , inlet valve  20 , diaphragm  22 , pump chamber  24 , outlet valve  26 , hydraulic cylinder  28 , piston  30 , and boot seal  32 . Inlet valve  20  controls the flow of fluid through inlet  34  and comprises ball  36  and seat  38 . Outlet valve  26  controls the flow of fluid through outlets  40  and comprises ball  44  and seat  42 . Diaphragm  22  is disposed within pump chamber  24  and provides a flexible membrane allowing the transfer of hydraulic forces, i.e. pressure, but not fluid between the pumped fluid from the wellbore and the hydraulic fluid in the pump.  
         [0020]     Pumped fluid flows from the wellbore, through inlet valve  20 , and into pump chamber  24 . The fluid exits pump chamber  24  through outlet valve  26  and into the tubing string above pump  10 . Pump chamber  24  is a constant volume chamber and has rigid boundaries. Diaphragm  22  divides pump chamber  24  into a pumped fluid chamber  46 , which is connected to valves  20  and  26 , and a hydraulic fluid chamber  48 , which is in fluid communication with hydraulic cylinder  28 .  
         [0021]     Piston  30  is moveably disposed within hydraulic cylinder  28 . Seals  47  engage the wall of cylinder  28  and divide the cylinder into an upper chamber  50  and a lower chamber  52 . Both upper chamber  50  and lower chamber  52  are filled with a fixed volume of hydraulic fluid that is preferably a clean, dry hydraulic oil. Upper chamber  50  is isolated from the wellbore by boot seal  32  which sealingly engages pump body  18  and piston  30  and allows for volumetric changes in the upper chamber. Lower chamber  52  is fluidly connected to hydraulic fluid chamber  48 .  
         [0022]     Piston  30  is coupled to reciprocating rod  12  via connecting rod  14  and couplings  16 . As piston  30  is moved upward by reciprocating rod  12 , hydraulic fluid is drawn from hydraulic fluid chamber  48  into lower chamber  52 . This decreases the fluid volume in hydraulic fluid chamber  48  and causes diaphragm  22  to expand. The expansion of diaphragm  22  closes outlet valve  26 , opens inlet valve  20 , and draws fluid through inlet  34  into the diaphragm. The upward movement of piston  30  also causes boot seal  32  to expand.  
         [0023]     Once reciprocating rod  12  has reached the upward limit of its stroke it reverses direction and moves downward. As piston  30  is moved downward by reciprocating rod  12 , hydraulic fluid is pushed back into hydraulic fluid chamber  48  from lower chamber  52 . This increases the fluid volume in hydraulic fluid chamber  48  and causes diaphragm  22  to contract. The contraction of diaphragm  22  closes inlet valve  20 , opens outlet valve  26 , and pushes fluid through out of the diaphragm and through outlets  40 . The downward movement of piston  30  also causes boot seal  32  to contract.  
         [0024]     Thus, the reciprocation of hydraulic fluid into and out of hydraulic fluid chamber  48  causes pumped fluid to move through valves  20  and  26  and into and out of the diaphragm  22 , causing a pumping action. Boot seal  32  and diaphragm  22  provide static seals that help to assure a complete seal and long life for the pump. This arrangement also assures that pumped fluid never comes into contact with dynamic seals  46  located on piston  30 . The linear movement of reciprocating rod  12  and piston  30  is preferably designed such that diaphragm  22  is substantially emptied on each stroke. In certain embodiments, piston  30  is designed to have a potential stroke distance that is about 50% larger then the actual stroke of reciprocating rod  12  so as to accommodate mechanical alignment and rod stretch.  
         [0025]     Pump dynamics are also improved as the delivery stroke is the downstroke rather then the upstroke as in conventional rod pumps. This allows the weight of the reciprocating rod  12 , rather then the lifting force provided by the surface unit, to be the driving force delivering fluid from pump  10  to the surface. The use of a viscous hydraulic fluid to transmit pressure between hydraulic cylinder  28  and the pump chamber  24 , with appropriate restrictions  43  between the two, can eliminate rod pound by providing slowing of the downward motion of the reciprocating rod  12  when pumping gas. Such a viscous connection provides increased resistance to the movement of piston  30  when high velocities may be encountered due to a lack of resistance that may occurs, such as when gas is drawn into diaphragm  22 .  
         [0026]     In certain embodiments, pump assembly  10  is installed downhole on reciprocating rod  12 . Referring now to  FIG. 2 , the lower end of pump  10  is fitted with a mechanical, or cup-type, bottom hold down system  58  to attach the pump to landing nipple  56  in tubing string  54 . This embodiment is installed in the same way as a standard insert rod pump, and can directly replace almost any standard downhole rod pump.  FIG. 3  illustrates an alternate hold down system for pump  10  where the pump is coupled to tubing string  60  via the engagement of top hold down system  64  with landing nipple  62 . Both top and bottom hold down systems are well known in the art.  
         [0027]     As shown in  FIGS. 2 and 3 , pump  10  may further comprise check valve  70  disposed on piston  30 . Check valve  70  comprises seat  72 , ball  74 , and biasing member  76 . Check valve  70  provides selective fluid communication between upper chamber  50  and lower chamber  52 . Biasing member  76  urges ball  74  into sealing engagement with seat  72  preventing fluid communication between upper chamber  50  and lower chamber  52 . As piston  30  moves downward, pressure within lower chamber  52  increases. As the fluid within lower chamber  52  reaches a predetermined pressure, the differential pressure across ball  74  will compress biasing member  76 . The compression of biasing member  76  opens check valve  70  and allows fluid communication between lower chamber  52  and upper chamber  50  so that the pressure within the chambers will equalize.  
         [0028]     Check valve  70  and biasing member  76  are selected such that the valve opens at a predetermined pressure that is less than the failure pressure of diaphragm  22 . Thus, valve  70  prevents damage to diaphragm  22  due to overpressurization. Check valve  70  compensates for pump setting variations, and other variations in volume of fluid due to leakage, thermal expansion, or other factors. In other embodiments, a small orifice through piston  30  may be used in place of check valve  70 .  
         [0029]     Referring now to  FIG. 4 , a tubing-mounted pump  100  is shown. Pump  100  comprises body  118 , inlet valve  120 , diaphragm  122 , pump chamber  124 , outlet valve  126 , hydraulic cylinder  128 , piston  130 , check valve  131 , and boot seal  132 . Pump  100  is attached to tubing string  102  and installed into a well with the tubing string. Reciprocating rod  112  is then run into tubing string  102  and connected to piston  130  via releasable coupling  116 . Coupling  116  may be a mechanical hold down assembly, such as Harbison-Fischer part number 7381H1b, engaging a standard F-type seating nipple. Coupling  116  is designed to remain connected until the pulling force exceeds a selectable maximum, at which time, the coupling disengages, allowing the reciprocating rod  112  to be pulled from the well separately from tubing string  102 .  
         [0030]     The reciprocating movement of rod  112  operates pump  100  in the same manner as described in relation to pump  10  above. In general, as piston  130  moves upward, hydraulic fluid is drawn into hydraulic cylinder  128  from pump chamber  124 , expanding diaphragm  122  and drawing fluid through inlet valve  120 . As piston  130  moved downward, hydraulic fluid is forced back into pump chamber  124 , collapsing diaphragm  122  and pushing fluid into tubing string  102  through outlet valve  126 . Check valve  131  provides fluid communication across piston  130  so as to limit the fluid pressure acting on diaphragm  122 . Mounting pump  100  to tubing string  102  allows for a larger diameter pump to be used which in turn allows for a larger diaphragm  122  and an increased pumping capacity.  
         [0031]     Referring now to  FIG. 5 , submersible pump  150  is coupled to a reciprocating rod  162  via connecting rod  164  and couplings  166 . Pump  150  comprises body  168 , inlet valve  170 , diaphragm  172 , pump chamber  174 , outlet valve  176 , hydraulic cylinder  178 , piston  180 , piston seals  182 , and wiper seal  184 . As with pump  10 , as piston  180  moves upward, hydraulic fluid is drawn into hydraulic cylinder  178  from pump chamber  174 , expanding diaphragm  172  and drawing fluid through inlet valve  170 . As piston  180  moved downward, hydraulic fluid is forced back into pump chamber  174 , collapsing diaphragm  172  and pushing fluid through outlet valve  176 .  
         [0032]     Wiper seal  184  provides an effective seal that engages piston  180  and minimizes the loss of hydraulic fluid. Wiper seal  184  may preferably be used in less severe environments where fluid loss and seal wear is not expected on the wiper. Although the boot seal of pump  10  may form a better seal, wiper  184  will, in many environments, effectively accomplish the same job while being less complicated and more compact.  
         [0033]     Some current wells utilize rotating rods, as an alternative to reciprocating rods, to provide power to submersible pumps.  FIG. 6  illustrates a submersible pump  200  configured for use with a rotating rod  212 . Pump  200  comprises body  218 , inlet valve  220 , diaphragm  222 , pump chamber  224 , outlet valve  226 , expansion element  227 , hydraulic cylinder  228 , piston  230 , check valve  231 , and barrel cam  232 . Pump  200  is connected to rotating rod  212  by coupling  216 . A non-contact coupling, such as a magnetic coupling, can be used to seal the pump assembly without the use of dynamic seals.  
         [0034]     The rotation of rod  212  causes barrel rod  234  to rotate and barrel body  236  and piston  230  to reciprocate within hydraulic cylinder  228 . As piston  230  moves upward, hydraulic fluid is drawn into hydraulic cylinder  228  from pump chamber  224 , expanding diaphragm  222  and drawing fluid through inlet valve  220 . Expansion element  227  is constructed from an expandable material so as to compensate for the change in volume of chamber  228  as piston  230  moves. As piston  230  moves downward, hydraulic fluid is forced back into pump chamber  224 , collapsing diaphragm  222  and pushing fluid through outlet valve  226 . Check valve  231  provides fluid communication across piston  230  so as to limit the fluid pressure acting on diaphragm  222 .  
         [0035]     Although the submersible pump systems shown and described herein use sucker rods activated by existing drive systems, such as reciprocating rod pump drive heads or progressing cavity rotating rod drive heads to operate the pump, other methods, such as using a cable and weight system to operate a reciprocating pump, are also possible. The embodiments shown and described herein provide a mechanically actuated hydraulic diaphragm pump that can utilize the motion of a rotating and/or reciprocating rod string to operate the pump. The preferred pump systems isolate the pumped fluid from the working fluid with one or more flexible diaphragms and/or sealing systems. The systems can be designed to work in the same way, and use the same infrastructure, e.g. surface units, rod strings, hold down systems, balls and seats, installation methods, etc., as conventional rod pump bottom hole assemblies, but operate using a diaphragm pump instead of a conventional piston-cylinder pump or progressing cavity pump.  
         [0036]     While preferred embodiments of this invention have been shown and described, modifications thereof can be made by one skilled in the art without departing from the scope or teaching of this invention. The embodiments described herein are exemplary only and are not limiting. Many variations and modifications of the system and apparatus are possible and are within the scope of the invention. For example, the relative dimensions of various parts, the materials from which the various parts are made, and other parameters can be varied, so long as the apparatus retain the advantages discussed herein. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims.