Patent Application
20080080991
So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
A method and apparatus for lifting fluids from a well is provided. In one embodiment, a pump assembly comprises a rotary motor adapted to actuate a reciprocating pump. The motor shaft of the rotary motor is coupled to a drive member of the reciprocating pump. In operation, rotation of the rotary motor causes reciprocation of the reciprocating pump.
A motor seal 115 may be used to couple the motor 110 to the pump 100. The motor seal 115 allows for oil expansion as the pump 100 is reciprocated. Preferably, the motor seal 115 is a barrier type seal having a metal bellow or an elastomeric diaphragm or bag. Other suitable motor seals known to a person of ordinary skill are also contemplated.
In one embodiment, the pump 100 includes a housing 112 having one or more ports 113 for fluid communication with the wellbore 10. An expandable member 120 in the housing 112 fluidly seals off an interior portion 111 of the pump 100 from the wellbore fluids. Suitable expandable members include a diaphragm and a bellow.
The expandable member 120 is retracted or expanded using a ball screw type coupling with the motor shaft 125 of the motor 110. As shown in
A reciprocating member 140 connected to the plate 122 extends from the plate 122 and into an upper portion of the housing 112. The reciprocating member 140 includes an arm portion 143 and a valve portion 142. The valve portion 142, also known as the traveling valve, is adapted to selectively control the flow of wellbore fluids into and out of the fluid chamber 145. The fluid chamber 145 is defined by the traveling valve 142, a standing valve 150 and the housing 112. Each of the traveling valve 142 and the standing valve 150 includes a seat for mating with a seal member 141, 151. An exemplary seal member is a ball. The traveling valve 142 is adapted to allow inflow to the fluid chamber 145, while the standing valve 150 is adapted to allow outflow from the fluid chamber 145. The arm portion 143 is adapted and arranged to maintain the traveling valve 142 above the ports 113 such that during the downstroke, wellbore fluids entering the ports 113 may flow through the traveling valve 142 and into the fluid chamber 145.
In operation, the pump 100 acts as a reciprocating positive displacement pump to deliver wellbore fluids to the surface. As shown in
The nut 130 also imparts a downstroke to the reciprocating arm 140, thereby increasing the size of the fluid chamber 145. As the fluid chamber 145 is increased, the pressure in the fluid chamber 145 decreases. As the pressure decreases, the pressure differential between the inside and the outside of the fluid chamber 145 increases, thereby creating a vacuum like effect inside the fluid chamber 145. The strength of the vacuum is dependent on the length of travel of the traveling valve 141. The downstroke of the reciprocating arm 140 creates a vacuum sufficient to cause the ball 141 of the traveling valve 142 to unseat so that wellbore fluids are drawn upward into the fluid chamber 145. During this time period, the standing valve 151 preferably remains closed.
After the fluid chamber 145 is filled sufficiently with wellbore fluids, the motor 110 is rotated in the opposite direction to begin the upstroke of the pump 100. The opposite rotation causes the nut 130 to reverse directions and move away from the motor 110, i.e., upstroke. This motion expands the diaphragm 120 and draws the oil away from the motor seal 115. In this respect, reciprocation of the pump 100 may be accomplished by changing the rotational direction of the motor shaft 125.
During this upstroke, the traveling valve 142 is moved closer to the standing valve 150, thereby compressing the fluid chamber 145. In turn, the pressure in the fluid chamber 145 increases, which forces the ball 151 of the standing valve 150 to unseat. Opening of the standing valve 150 allows fluids in the fluid chamber 145 to be delivered to the production tubing 20. In this manner, wellbore fluids may be delivered by positive displacement toward the surface.
In another embodiment, the reciprocating pump 700 may be driven by a hydraulic pump 715 operated by a permanent magnet motor 710.
The expandable member 720 may be retracted or expanded using the hydraulic pump 715. An exemplary hydraulic pump suitable for use is a swash-plate hydraulic pump capable of providing high working pressure with high reliability. The hydraulic pump 715 may be driven by the permanent magnet motor 710 either directly or using a gearbox. One advantage of direct drive is reliability in long-term continuous operation. As shown, the hydraulic pump 715 and the motor 710 are immersed in the working fluid in the interior portion 711. In this respect, no motor seals are required.
The hydraulic pump 715 is connected to a piston 735 and cylinder 730 assembly adapted to reciprocate the expandable member 720. In one embodiment, the cylinder 730 includes a fluid chamber 731, 732 on each side of the piston 735. The piston 735 is extended or retracted by alternately directing the hydraulic pump output 740 into each chamber 731, 732. The piston 735 is connected to an upper portion (e.g., plate 722) of the expandable member 720 such that as the piston 735 is alternately extended and retracted, the expandable member 720 is reciprocated. Electronically operated hydraulic valves 751, 752 may be provided to control the flow of the hydraulic pump output 740 to the respective chambers 731, 732 of the cylinder 730. The electrical circuit of the valves 751, 752 may detect movement of the piston 735 and switch the valves 751, 752 in sympathy in accordance with the detected response. The piston 735 may optionally include a lower protrusion 736 to ensure the working surface on each side of the piston exerts the same force for the same injected pressure.
In operation, the motor 710 may be operated continuously in one direction to drive the hydraulic pump 715, which, in turn, may be adapted to reciprocate a reciprocating arm 140, as described with respect to
When the electrical circuit detects the piston 735 is at its upper travel limit, the electrical circuit switches the valves 751, 752 in sympathy. In this respect, the lower valve 752 is de-energized to allow the lower chamber 732 to drain and the upper valve 751 is energized to allow the upper chamber 731 to fill. In this manner, the piston 735 is urged downward to retract the expandable member 720, thereby placing the reciprocating arm 140 in a downstroke. The downstroke increases the size of the fluid chamber 145, which results in a pressure decrease in the fluid chamber 145. As the pressure decreases, the pressure differential between the inside and the outside of the fluid chamber 145 increases, thereby creating a vacuum like effect inside the fluid chamber 145. The strength of the vacuum is dependent on the length of travel of the traveling valve 141. The downstroke of the reciprocating arm 140 creates a vacuum sufficient to cause the ball 141 of the traveling valve 142 to unseat so that wellbore fluids are drawn upward into the fluid chamber 145. During this time period, the standing valve 151 preferably remains closed. After the fluid chamber 145 is filled sufficiently with wellbore fluids, the lower valve 752 is energized and cycle restarts.
In another embodiment, a check valve is used 242, and the traveling valve 142 is eliminated.
In another embodiment, the motor 310 may be coupled to two pumps 300, 400, as shown in
One advantage of this two pump system is that clean fluid in the interior portions 311, 411 of the pumps 300, 400 can pass from the top pump 300 to the bottom pump 400. While movement of the plate 122 and bellows 120 increases or decreases the volume in the interior portion 311 in one pump 300, an equal change in volume is occurring in the other pump 400. Therefore, the motor seal 315 does not need to compensate for the changing volume in the interior portions 311, 411. It should also be noted that the fluid in the interior portions 311, 411 may be clean oil that is used to cool and lubricate the motor 310. The transfer of oil transferred from one pump 300 to the other pump 400 may provide additional cooling for the motor 310.
Referring back to
The pump assembly 501 further comprises two pump chambers 511, 521 for accumulating formation fluids (also referred to as “pumped fluids.”) As shown, the pump chambers 511, 512 are stacked above one another. In another embodiment, the pump chambers may be positioned side by side. Each of the chambers 511, 521 is provided with a set of check valves 515, 516, 525, 526 for controlling the inflow and outflow of formation fluids. In this embodiment, inlet valves 515, 525 allow formation fluids to flow into their respective pump chambers 511, 521, and outlet valves 516, 526 allow the fluids accumulated in the pump chambers 511, 521 to flow out into the production tubing 20.
Each of the pump chambers 511, 521 are associated with a respective diaphragm 512, 522. The diaphragms 512, 522 control the volume available for retaining the formation fluid in each chamber 511, 521. The diaphragms 512, 522 are at least partially disposed within the chamber 511, 521 and are fluidly isolated from the formation fluids in the chamber 511, 521. Because the diaphragms 512, 522 are fluidly sealed from the formation fluid, inflation of the diaphragm 512, 522 will decrease the volume in the chamber 511, 521 available for accumulating formation fluids, while deflation of the diaphragm 512, 522 will increase the volume available for retaining formation fluids.
The diaphragms 512, 522 are inflated or deflated by an operating fluid pumped by the electrical submersible pump 500. The operating fluid may be a hydraulic fluid or other suitable incompressible fluid. In the preferred embodiment, the pump 500, diaphragms 512, 522, and the operating fluid form a closed hydraulic system. In this respect, the diaphragms 512, 522 share the same operating fluid, and a portion of the operating fluid from one diaphragm 512, 522 may be transferred to or from the other diaphragm 512, 522 depending on the direction of the pump 500. As a result, withdrawal of a portion of the operating fluid from one diaphragm 512, 522 will cause that diaphragm 512, 522 to deflate, while introduction of that portion of operating fluid to the other diaphragm 512, 522 will cause that diaphragm 512, 522 to inflate. In this respect, the two pump chambers 512, 522 operate at different phases of the pump cycle. In this manner, the two pump chambers 512, 522 may advantageously operate simultaneously to pump formations fluids to the surface.
In operation, the pump 500 is operated to pump operating fluid from the first diaphragm 512 to the second diaphragm 522, thereby deflating the first diaphragm 512 and inflating the second diaphragm 522. In turn, the volume of the first chamber 511 is increased. As the volume increases, the pressure in the first chamber 511 is reduced, thereby drawing in formation fluid through the first inlet check valve 515 to fill the first chamber 511. During filling, the first outlet check valve 516 is preferably closed or substantially closed. On the other hand, inflation of the second diaphragm 522 causes a reduction in the volume of the second chamber 522, thereby discharging the formation fluids accumulated in the second chamber 522. The formation fluids are expelled through the second outlet check valve 526, which leads to the production tubing 20. During this time, the second inlet check valve 525 is closed to prevent the formation fluids from returning into the wellbore.
After the second chamber 512 has expelled a sufficient amount of formation fluids, the second chamber 512 is ready for the filling phase, while the first chamber 511 is ready for the discharge phase. To make the transition, the motor 510 is rotated in the opposite direction to cause the pump 500 to pump the operating fluid in the opposite direction, thereby deflating the second chamber 521 and inflating the first chamber 511. In this respect, the diaphragm 512 in the first chamber 511 is expanded to force the accumulated formation fluids out of the chamber 511 and into the production tubing 20, while the diaphragm 522 in the second chamber 521 is retracted to draw formation fluids into the second chamber 521. In this respect, the pump 500 may be operated to alternately drive formation fluids to the surface. The use of a rotary motor that can rotate in at least two different directions provides an efficient manner of producing fluids to the surface.
To initiate the fill cycle in the first chamber 611, working fluid is moved from the first diaphragm 612 to the second diaphragm 622. Movement of the working fluid to the second diaphragm 622 initiates the discharge cycle in the second chamber 621. To discharge the accumulated fluid in the first chamber 611, the rotation of the motor 510 is reversed. In one embodiment, the motor rotation is reversed by reversing the phase sequence of the coils in the permanent magnet motor. The change in motor rotation results in a change in the flow of the operating fluid, now out of the second diaphragm 622 and into the first diaphragm 612. As a result, the first diaphragm 612 is expanded, there by forcing the accumulated formation fluid out of the first chamber 611, and the second diaphragm 622 is retracted, thereby by drawing in formation fluid to fill the second chamber 621.
In another embodiment, the diaphragms 612, 622 may be driven by the hydraulic pump 715 and motor 710 described with respect to
While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.
