Patent Application
20070110597
Not Applicable.
Not Applicable.
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.
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.
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.
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.
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.
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.
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.
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.
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.
For a more detailed description of the preferred embodiment of the present invention, reference will now be made to the accompanying drawings, wherein:
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.
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.
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.
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.
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.
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.
In certain embodiments, pump assembly 10 is installed downhole on reciprocating rod 12. Referring now to
As shown in
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.
Referring now to
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.
Referring now to
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.
Some current wells utilize rotating rods, as an alternative to reciprocating rods, to provide power to submersible pumps.
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.
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.
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.
