ROD-PUMPING SYSTEM
A rod-pumping system is provided. In one embodiment, the system includes a downhole pump positioned in a well and coupled to a well string, such as a sucker-rod string. The system also includes a first hydraulic actuator arranged with respect to the well string so as to enable the first hydraulic actuator to move the well string within the well. The first hydraulic actuator is connected in fluid communication with a second hydraulic actuator. A control pump is connected to both the first and second hydraulic actuators to enable the control pump to alternate between pumping control fluid to the first hydraulic actuator to cause the well string to move in a first direction within the well and pumping control fluid to the second hydraulic actuator to cause the well string to move in an opposite, second direction within the well. Additional systems, devices, and methods are also disclosed.
This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the presently described embodiments. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present embodiments. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
In order to meet consumer and industrial demand for natural resources, companies often invest significant amounts of time and money in finding and extracting oil, natural gas, and other subterranean resources from the earth. Particularly, once a desired subterranean resource such as oil or natural gas is discovered, drilling and production systems are often employed to access and extract the resource. These systems may be located onshore or offshore depending on the location of a desired resource. Further, such systems generally include a wellhead assembly mounted on a well through which the resource is accessed or extracted. These wellhead assemblies may include a wide variety of components, such as various casings, valves, pumps, fluid conduits, and the like, that control drilling or extraction operations.
In some instances, resources accessed via wells are able to flow to the surface by themselves. This is typically the case with gas wells, as the accessed gas has a lower density than air. This can also be the case for oil wells if the pressure of the oil is sufficiently high to overcome gravity. But often accessed oil does not have sufficient pressure to flow to the surface and the oil must be lifted to the surface through one of various methods known as artificial lift. Artificial lift can also be used to raise other resources through wells to the surface, or for removing water or other liquids from gas wells. One form of artificial lift uses a pump that is placed downhole in the well and is operated by a reciprocating rod string extending through the well from the downhole pump to the surface. Such systems are commonly referred to as rod-pumping or sucker-rod systems.
SUMMARYCertain aspects of some embodiments disclosed herein are set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of certain forms the invention might take and that these aspects are not intended to limit the scope of the invention. Indeed, the invention may encompass a variety of aspects that may not be set forth below.
Embodiments of the present disclosure generally relate to a rod-pumping system for lifting fluids from a well. The rod-pumping system of one embodiment includes a pair of hydraulic actuators, such as hydraulic cylinders; a rod string moved by one of the hydraulic actuators and coupled to a downhole pump; and a control pump. The hydraulic actuators are connected in series, and the control pump is connected to pump fluid to one end of each hydraulic actuator such that alternating the flow direction from the control pump controls operation of the hydraulic actuators and operates the downhole pump via the rod string. In some embodiments, sensors are used to detect the positions of pistons in the actuators and a controller synchronizes the pistons to facilitate proper operation.
Various refinements of the features noted above may exist in relation to various aspects of the present embodiments. Further features may also be incorporated in these various aspects as well. These refinements and additional features may exist individually or in any combination. For instance, various features discussed below in relation to one or more of the illustrated embodiments may be incorporated into any of the above-described aspects of the present disclosure alone or in any combination. Again, the brief summary presented above is intended only to familiarize the reader with certain aspects and contexts of some embodiments without limitation to the claimed subject matter.
These and other features, aspects, and advantages of certain embodiments will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
One or more specific embodiments of the present disclosure will be described below. In an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.
When introducing elements of various embodiments, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. Moreover, any use of “top,” “bottom,” “above,” “below,” other directional terms, and variations of these terms is made for convenience, but does not require any particular orientation of the components.
Turning now to the present figures, a system 10 is illustrated in
The system 10 also includes an artificial lift system 18. In one embodiment generally depicted in
As depicted in
The artificial lift system 18 depicted in
The auxiliary pump 34 is connected to provide fresh control fluid (i.e., new or reconditioned control fluid) to at least some portions of the hydraulic circuit that includes the slave cylinder 26 and the master cylinder 28. The auxiliary pump 34 can also, but need not, draw control fluid from the fluid tank 38 and be driven by the prime mover 36 independent of the control pump 32. (It is noted that taking a slip stream off of the control pump circuit to feed the auxiliary pump 34, while possible, would reduce system speed.) In one embodiment, control fluid is flushed from various portions of the hydraulic circuit (e.g., with one or more flushing valves) and replaced by fresh control fluid pumped from the fluid tank 38 by the control pump 32 and the auxiliary pump 34. The flushed control fluid can be routed through a conditioning system 40, such as through one or more filters to remove any contaminants in the control fluid and through a cooler that lowers the temperature of the control fluid to reduce wear on components of the artificial lift system 18. Control fluid reconditioned by the conditioning system 40 can be returned to the fluid tank 38 to be reused in the pumping system 30.
The pumping system 30 also includes a controller 42. The controller 42 processes inputs from various sensors 44 to control operation of other components of the pumping system 30 (e.g., the control pump 32, the auxiliary pump 34, the prime mover 36, any flushing valves, and the cooler of the conditioning system 40) and, by extension, operation of the slave cylinder 26 and the master cylinder 28. In some embodiments, the sensors 44 include proximity switches and a linear position transducer that allow the determination of positions of pistons within the slave cylinder 26 and the master cylinder 28. The sensors could also, for example, include a temperature sensor to monitor temperatures of control fluid or components in the artificial lift system 18, pressure sensors to detect hydraulic pressures at various locations within the system 18, or a level sensor to detect the amount of control fluid available in the fluid tank 38. The controller 42 in one embodiment is a programmable logic controller that is programmed to provide the control functionality described herein. But in other embodiments, the controller 42 could be any circuit-based device (with or without software) suitable for controlling operation of the artificial lift system 18, such as a processor-based device that executes instructions (firmware or software) stored in a suitable memory of the device.
The depicted pumping system 30 also includes a skid 46 to facilitate transport of various system components. For example, in one embodiment the primary pump 32, the auxiliary pump 34, the prime mover 36, the fluid tank 38, the conditioning system 40, the controller 42, and some sensors 44 are provided on the skid 46, allowing an operator to more easily move all of these components to a desired location. Other components, such as the master cylinder 28, can also be mounted on the skid 46.
As noted above, the slave cylinder 26 engages the sucker-rod string 22 to operate the downhole pump 24 and lift fluid up the well 14 to the surface. The slave cylinder 26 can be attached to wellhead equipment to receive the sucker-rod string 22 and operate the downhole pump 24. One example of such an arrangement is depicted in
The wellhead equipment 16 also includes a stuffing box 60 attached to the tubing head 54. As will be recognized by those knowledgeable in the art, the stuffing box 60 includes packing that allows the polished rod 50 to move up-and-down through the stuffing box 60 while inhibiting leaking. The polished rod 50 is connected to a series of sucker rods to form the sucker-rod string 22 that extends through the well 14 to the downhole pump 24. Movement of the polished rod 50 causes corresponding movement of the sucker rods to operate the downhole pump 24. In other embodiments, the stuffing box 60 is omitted and the slave cylinder 26 itself isolates wellbore fluids from the external environment.
The slave cylinder 26 includes a housing 66 in which a piston rod 68 is disposed. The piston rod 68 of the depicted embodiment is hollow (see
As depicted in
As noted above, the connecting rod 70 is positioned with respect to the piston rod 68 and is coupled to the sucker-rod string 22 to enable the movement of the piston rod 68 to operate the downhole pump 24. In the embodiment depicted in
In at least some embodiments, the slave cylinder 26 includes one or more sensors to detect the position of the piston head 92 within the housing 66. Any suitable sensor could be used, such as a proximity switch or a linear transducer. In one embodiment depicted in
Certain operational aspects of the rod-pumping system described above may be better understood with reference to
The master cylinder 28 is arranged in series with the slave cylinder 26, with the chamber 128 connected in fluid communication with the chamber 96 on the cap end of the slave cylinder 26. Primary pump 32 is connected in fluid communication with both the chamber 130 and the chamber 98 on the rod end of the slave cylinder 26. Pressurized hydraulic fluid in the chambers 128 and 130 may be manipulated to act on the piston head 122 and move the piston 120 within the master cylinder 28. The master cylinder 28 in
The system depicted in
In one embodiment, the one or more accumulators 136 are set (e.g., pre-charged) to counterbalance the full load of the slave cylinder 26 during operation. That is, the force on the master cylinder piston 120 caused by the one or more accumulators 136 meets or exceeds the load on the slave cylinder piston due to gravity (which includes loading by the components borne by the piston rod 68, such as the sucker-rod string 22 and any portion of the downhole pump 24 connected to move with the sucker-rod string 22). This fully counterbalanced arrangement is in contrast to systems in which the load on the slave cylinder is only partially counterbalanced. In such partially counterbalanced systems, upstrokes rely on pressure from control pumps to provide sufficient force to overcome gravitational loading on pistons of slave cylinders coupled to a rod string and the systems rely on gravity to retract the slave cylinder piston and push the master cylinder piston back toward accumulators. But having the primary pump 32 control one side of the slave cylinder 26, as described above, reduces or eliminates the reliance on gravity to retract the slave cylinder piston, allowing the counterbalance pressure from the accumulators 136 to be set at or above the load on the slave cylinder piston.
In one embodiment, the biasing force from the accumulators 136 balances the full load on the piston of slave cylinder 26, and the primary pump 32 is used to offset this hydraulic balance between the cylinders to provide directional control and speed control of the piston rod 68 (and, by extension, of the sucker-rod string 22). As one line from the primary pump 32 is connected to the rod end of the slave cylinder 26 (rather than the pump having direct control over the reciprocating of the master cylinder 28 by being directly connected to both sides of its piston), the pistons of the two cylinders move in consort based on differential pressures. Such an arrangement allows the use of a differential cylinder (e.g., slave cylinder 26) in a closed-loop system without venting to atmosphere. This is in contrast to other arrangements that rely on gravity to reset the piston of a slave cylinder and in which the rod end of the slave cylinder is vented to atmosphere so as to not inhibit movement of the piston. By not venting the rod end of the slave cylinder 26 to atmosphere, the present arrangement avoids large pressure differentials across seals provided on piston head 92 to isolate the chambers 96 and 98 (such pressure differentials could contribute to premature seal failure) and reduces the likelihood of rust and contamination of the rod end components of the slave cylinder 26, like piston rod 68.
In at least some embodiments, the master cylinder 28 is constructed proportionally to the slave cylinder 26 to have larger piston heads and a shorter stroke. The connection of the primary pump 32 to both the slave cylinder 26 and the master cylinder 28 in the manner depicted in
During normal operation of the hydraulic system depicted in
To facilitate proper operation, the controller 42 receives inputs from various sensors and controls the pumping system components to synchronize the cylinders 26 and 28. Sensors (e.g., proximity switches 110 and 112, and linear position transducer 138) facilitate determination of the positions of the cylinder pistons. Based on this information, the controller 42 can synchronize the cylinders 26 and 28. More specifically, at startup, the controller 42 determines whether the cylinders are synchronized. If they are not, the controller 42 automatically synchronizes the cylinders before starting normal operation of the system. That is, the controller 42 operates the pumps 32 and 34, the flushing valves, or both to vary the amount of fluid in the various chambers and, consequently, to adjust the distance between the piston heads 92 and 122 in the circuit such that the pistons of both cylinders 26 and 28 can travel their intended stroke lengths during operation. As one example, such synchronization can be achieved by pumping control fluid with the primary pump 32 into chamber 98 to retract the piston rod 68 and then varying the amount of fluid in chamber 128 (to properly space the piston head 122 with respect to the piston head 92) by either pumping additional fluid into the chamber 128 with the auxiliary pump 34 or by flushing fluid from chamber 128. Such synchronization of the cylinders 26 and 28 can also be based on other inputs, such as feedback from other sensors 144 (e.g., pressure sensors in the hydraulic circuit, temperature sensors, and a level sensor in the fluid tank 38 (
In some embodiments, the controller 42 provides additional control functionality. For instance, the controller 42 can vary operation of the hydraulic system based on temperature detected by one or more temperature sensors. On a cold startup, the controller 42 may operate the system at a reduced speed (e.g., operate the primary pump at a set percentage of maximum flow) until a desired system temperature is achieved. This may reduce cavitation of the pumps and damage to seals and filter elements in the system. And during operation, the controller 42 can cause operation of the system to be slowed if the detected temperature exceeds a first threshold temperature and stopped if the detected temperature exceeds a second, higher threshold. It is noted that continued operation at a reduced speed allows hydraulic fluid to be passed through a cooler of the conditioning system 40, which may allow the system to cool faster than if the system were simply stopped.
Additionally, the controller 42 may provide an emergency alarm or shut-off function to stop undesirable operation of the system, which may include motion of the piston 120 outside of a desired range. By way of example, the master cylinder 28 and the slave cylinder 26 may be configured such that the maximum volume of the chamber 128 exceeds that of chamber 96 to which it is hydraulically connected. Movement of the piston head 122 to the left in
Further, in some embodiments the controller 42 monitors the position of the piston 120 (via transducer 138) to facilitate synchronization and ensure the piston 120 is not traveling too close to the end of the master cylinder 28 at chamber 128. The controller 42 can be programmed with one or more threshold distances based on the allowable maximum travel of the piston 120. For example, if the distance from the end of the master cylinder 28 and the piston head 122 falls below a first, set threshold the controller 42 can trigger an alarm to alert an operator that the piston 120 is moving to a distance from the end of the cylinder that is near a minimum allowable distance. In addition to or instead of triggering an alarm, the controller 42 can automatically activate the auxiliary pump 34 to pump additional control fluid into the chamber 128 to try to push the piston 120 to the right in
Closed-loop hydraulic systems typically have sections of dead fluid (i.e., control fluid that cannot be removed from a hydraulic circuit for cooling or filtration). Additionally, synchronization between master and slave cylinders is maintained by trying to minimize fluid loss across seals of the system, and dead fluid resulting from trying to minimize fluid losses can lead to damage as the fluid degrades or is contaminated. But in some embodiments of the present technique, and as generally noted above, control fluid can be continually flushed from the different portions of the hydraulic circuit and replaced by fresh control fluid. The flushed fluid can be conditioned (e.g., filtered and cooled) via conditioning system 40 and returned to the hydraulic circuit or to the fluid tank 38. During such flushing and refilling, the controller 42 monitors the positions of the pistons of the cylinders 26 and 28 and can automatically keep or put the system back in synchronization by controlling the operation of the primary pump 32 and the auxiliary pump 34 to replace the flushed control fluid with a corresponding amount of fresh control fluid. In some embodiments, the auxiliary pump 34 operates independently from the primary pump 32 and pulls control fluid directly from the fluid tank 38, which has fluid that will be generally cooler and cleaner than fluid that could be drawn from the primary pump 32. For instance, in the embodiment depicted in
While the aspects of the present disclosure may be susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and have been described in detail herein. But it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the following appended claims.
Claims
1. A rod-pumping system comprising:
- a downhole pump positioned in a well;
- a well string coupled to the downhole pump;
- a first hydraulic actuator arranged with the well string so as to enable the first hydraulic actuator to move the well string within the well;
- a second hydraulic actuator connected in fluid communication with the first hydraulic actuator; and
- a control pump connected to the first hydraulic actuator and to the second hydraulic actuator in a manner that enables the control pump, during operation, to alternate between pumping control fluid to the first hydraulic actuator to cause the well string to move in a first direction within the well and pumping control fluid to the second hydraulic actuator to cause the well string to move in an opposite, second direction within the well.
2. The rod-pumping system of claim 1, wherein the control pump is connected to a rod end of the first hydraulic actuator.
3. The rod-pumping system of claim 1, wherein the second hydraulic actuator is connected to at least one accumulator set to counterbalance the full load of the first hydraulic actuator.
4. The rod-pumping system of claim 3, wherein the connection of the control pump to the first and second hydraulic actuators enables the control pump to offset hydraulic balance between the first and second hydraulic actuators.
5. The rod-pumping system of claim 1, comprising sensors to facilitate detection of piston positions in the first and second hydraulic actuators.
6. The rod-pumping system of claim 5, wherein the sensors include proximity switches that facilitate detection of the position of a piston of the first hydraulic actuator and a linear transducer that facilitates detection of the position of a piston of the second hydraulic actuator.
7. The rod-pumping system of claim 5, comprising a controller configured to receive input from the sensors that facilitate detection of the piston positions and to synchronize the first and second hydraulic cylinders.
8. The rod-pumping system of claim 1, comprising an auxiliary pump that enables the introduction of fresh control fluid to a hydraulic circuit that includes the first hydraulic actuator and the second hydraulic actuator.
9. The rod-pumping system of claim 1, wherein the first hydraulic actuator is a double-acting hydraulic cylinder.
10. The rod-pumping system of claim 1, wherein the first hydraulic actuator is coupled to a wellhead installed at the well.
11. The rod-pumping system of claim 1, wherein the well string includes a sucker-rod string that is coupled to a rod clamp that engages the first hydraulic actuator.
12. A rod-pumping system comprising:
- a slave cylinder mounted on or adjacent to wellhead equipment installed at a well;
- a master cylinder connected in fluid communication with the slave cylinder, wherein the master cylinder is counterbalanced with fluid from at least one accumulator and is able to absorb the full load of the slave cylinder; and
- a closed-loop hydraulic circuit including a pump connected in fluid communication with the slave cylinder and with the master cylinder to enable the pump to drive a piston in the slave cylinder and a piston in the master cylinder to reciprocate a well string within the well.
13. The rod-pumping system of claim 12, comprising an additional pump that enables hydraulic fluid to be pumped into the closed-loop hydraulic circuit to replace used hydraulic fluid flushed from the closed-loop hydraulic circuit.
14. The rod-pumping system of claim 13, comprising a prime mover coupled to drive both the pump and the additional pump.
15. The rod-pumping system of claim 12, comprising:
- position sensors on the slave cylinder and the master cylinder; and
- a controller configured to synchronize the slave cylinder and the master cylinder based on input from the position sensors.
16. The rod-pumping system of claim 12, comprising a downhole pump coupled to the well string.
17. A method comprising:
- lowering a well string that is positioned in a well and is coupled to a downhole pump within the well by pumping control fluid to a first linear actuator; and
- raising the well string by pumping control fluid to a second linear actuator that is connected to the first linear actuator.
18. The method of claim 17, wherein pumping control fluid to the first linear actuator includes pumping control fluid to a rod end of the first linear actuator.
19. The method of claim 17, comprising:
- determining the positions of pistons within the first linear actuator and the second linear actuator; and
- synchronizing the first linear actuator and the second linear actuator based on the determined positions of the pistons.
20. The method of claim 17, comprising alternating flow of control fluid between the first linear actuator and the second linear actuator by reversing flow of a bidirectional pump connected to the first linear actuator and the second linear actuator.
21. The method of claim 17, comprising:
- continually flushing control fluid from a hydraulic or pneumatic circuit including the first and second linear actuators and replacing the flushed control fluid with fresh control fluid during operation of the first and second linear actuators; and
- maintaining synchronization between the first and second linear actuators during operation.
Type: Application
Filed: Feb 15, 2013
Publication Date: Aug 21, 2014
Applicant: ICI ARTIFICIAL LIFT INC. (Houston, TX)
Inventors: Nicholas Donohoe (Edmonton), Lee D. Basset (Lloydminster)
Application Number: 13/769,017
International Classification: F04B 19/00 (20060101);