Patent Application
20150071794
The present disclosure relates to an improved type of oilfield pumping unit used to reciprocate a down-hole rod pump. Historically, conventional oilfield pumping units used a “walking beam” pivoting on a ground-based support frame. The beam is rocked back and forth by a crank arm connected to a rotary gear-drive. The beam is typically connected to the rod string via a wire rope, and the reciprocating motion of the beam provides the reciprocal lifting and lowering of the rod string. These pumping units were relatively large, massive structures, necessitated by the overhung lifting loads.
More recently, hydraulically powered pumping units have become increasingly popular. In one configuration, a linear motion system employs a single hydraulic cylinder centered above or below the polished rod. Often, a mast is used to suspend a single hydraulic cylinder above the polished rod. The polished rod is directly coupled to the cylinder, and hydraulic pressure applied to the ring side of the piston causes the cylinder to retract, thus lifting the rods. The mast can be attached to the ground, the casing, or the tubing. Other configurations have employed an offset cylinder with one or more pulley wheels are attached to the rod-end of the cylinder. A wire rope passes across the pulley wheel such that one rope end is attached to the rod string and the other end is dead-lined. As the cylinder extends, the wire rope transmits a lifting motion to the rod string.
Described herein is a compact artificial lift hydraulic pumping system providing simplified installation, longer life and ease of maintenance. A beam is pivotally mounted to a wellhead, ground, or other anchor structure, and one or more hydraulic cylinders are asymmetrically mounted with respect to the beam. The mounting is designed to pivot and slide about the pivot so as to provide self-aligning lift forces to the down-hole pump rod string. The self-aligning nature of the pump system eliminates side loads on both the hydraulic cylinder and polished rod.
In some embodiments, the system comprises a beam asymmetrical and parallel to the polished rod. The base of the beam is pivotally or rigidly attached to the wellhead, tubinghead or casing and one or more hydraulic cylinders are mounted parallel but axially offset from the center of the pivoting beam. In some embodiments, the end of the hydraulic cylinder is attached to a traveling assembly that comprises a traveling head that rolls along a track formed by the profile of the beam. The polished rod is attached to the traveling head such that the reciprocating movement of the hydraulic cylinders is thus coupled to cause a similar movement of the rod string. In one embodiment, the traveling assembly comprises a rotating member, such as a sprocket or sheave, connected to the rod end of the hydraulic cylinder. The traveling assembly further includes a flexible linkage, such as a chain, cable, wire, or rope passing over the rotating member and providing a lifting force to the polished rod.
Some embodiments require no elevated mast to suspend a hydraulic cylinder above the polished rod. The entire pumping unit may be assembled at ground-level, and then pivotally erected into place. This can be done without the use of overhead lifting equipment such as a crane or boom truck. Some embodiments may be configured to lift the rods when hydraulic pressure is applied to cap end of the hydraulic cylinder and the cylinder is extending. In the prior art utilizing a single cylinder suspended above the well, the ring side of the cylinder must be used to lift the rods on the up-stroke. Since the ring side of the cylinder piston has less surface area than the cap side, this configuration requires higher hydraulic pressure to develop the force required to lift the rods.
In some embodiments, it may be desirable to suspend the hydraulic cylinder above the polished rod, using the retracting cylinder force to lift the rods from the well. Here again, the unit may be assembled at ground level and pivotally erected into place.
The embodiments described herein also have a number of inherent advantages over traditional hydraulic pumping units configured with wire rope sheaves. In the prior art, the wire rope often become a high wear item due to the physical limitations of the size of the sheave. While conventional “walking beam” pumping units are configured with a wire-rope bending radius of 70 inches or more, the prior art hydraulic units are typically configured with rope sheaves with a bending radius of 12 inches or less. This small diameter bending radius severely reduces the life of the wire rope, thus increasing maintenance cost, and increasing HSE risk due to frequency of wire rope failures. In contrast, to the rigidly mounted cylinders provided in the prior art, the embodiments described herein allow use of larger radius sheaves due to the freely pivoting nature of the cylinder attachment to the well structure. In such a case, the angle of the cylinder with respect to the polished rod would infinitely change as the cylinder passes between the retracted and extended position.
Other advantages are present with respect to multiple symmetrically arranged hydraulic cylinders. Some hydraulic pumping units require two or more specially designed hydraulic cylinders rigidly attached between upper and lower mounting plates, the illustrative embodiments may utilize a single cylinder configuration. Fewer cylinders would inherently reflect lower initial cost, as well as lower future maintenance cost. Further still, regardless of the number of hydraulic cylinders, these embodiments may utilize low-cost, commodity type hydraulic cylinder configured with pin and clevis end connections. These cylinders are less expensive than custom-manufactured cylinders with a ridged mounting base arrangement required in the prior art. In some embodiments, the cylinders may be rigidly attached to a vertical mounting beam at multiple points. Thus able to are better able to handle column loading than the base-mounted cylinders found in the prior art.
Still other advantages are present with respect to rigid mounted cylinder configurations, whether that be single or multiple cylinder configurations. Rigid mounting of the cylinders with respect to the polished rod requires a high degree of accuracy in manufacturing and installation so as to cause the lifting force to be aligned parallel and congruent with the polished rod. Yet even with such care, there may still be some slight misalignment. Such misalignment of rigidly mounted cylinders will inherently cause side loads and wear between the polished rod and the stuffing box, and between the hydraulic cylinder rod and the cylinder rod bushings. The gimbaled mounting presented in this illustrative embodiment overcome these deficiencies by providing pivoting and sliding degrees of freedom with respect to the wellhead mounting pins, thus allowing the lifting force to be always transmitted parallel to the polished rod.
The illustrative embodiments also overcome problems associated with low pressure wellhead fixtures. In contrast to the bolted flanged face tubing holder utilized in high pressure wellheads, many low pressure wellheads utilize hammer union pack-off assemblies, thus lacking any flat faced surfaces to which a base plate or cylinder mounting assembly could be bolted or fastened. The illustrative embodiments overcome that problem by utilizing existing, symmetrically opposed wellhead piping ports as a means of attachment.
Hydraulic pumping units require a directional shifting valve to cyclically change the flow of oil and the directional motion of the hydraulic cylinders. An electric limit switch that senses the end of each stroke of the hydraulic cylinder may be used to shift a solenoid operated hydraulic valve from one position to another. In an improved system, mechanical controls linked to the movement of the hydraulic cylinder travel may be utilized to shift a valve spool from either the “up” or “down” position to the other. A spring detent mechanism is required to snap the valve from one position to the other so as to prevent the hydraulic directional valve from being stuck in a center position where no oil flows to the cylinder, preventing completion of the stroke. Unfortunately, sudden reversal of direction of the cylinder caused by the snap action of a spring detent mechanism on the valve can cause tensile or buckling fatigue and failure of the down-hole rod string, in addition to accelerated wear from the shock loads on the hydraulic system. Soft shifting valve configurations can be used to reduce the acceleration and deceleration forces at the beginning and end of each stroke.
Hydraulic systems typically have an overall energy efficiency of between 75%-85%. The loss of motive energy is translated into heating of the hydraulic fluid. This heat must be removed in order to prolong the life of the hydraulic components. Fan-powered heat exchangers may be used to cool the hydraulic fluid. In certain applications, particularly in shallow well pumping applications, the volume of fluid pumped from the well may be sufficient to dissipate this excess heat. In this situation, a tube and shell heat exchanger may use the fluid pumped from the well as a medium to dissipate the heat from the hydraulic fluid. A temperature switch in the production fluid downstream of the heat exchanger could be used as a “pump-off” controller. Production fluid pumped from the well is normally at a constant temperature. As such, a higher than normal temperature reading after the heat exchanger would signal that the volume rate of the production fluid from the well is decreasing, thus indicating the well is approaching a pumped-off condition. This may trigger a control circuit to set the pumping unit to an idle or off state. Alternatively, a similar temperature monitoring circuit could monitor the hydraulic fluid temperature for the same purpose. In either case, a reset timer would be used to re-start the pump cycle at a pre-determined interval.
The following figures are included to illustrate certain aspects of the present disclosure, and should not be viewed as exclusive embodiments. The subject matter disclosed is capable of considerable modifications, alterations, combinations, and equivalents in form and function, without departing from the scope of this disclosure.
In the following detailed description of the illustrative embodiments, reference is made to the accompanying drawings that form a part hereof. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is understood that other embodiments may be utilized and that logical structural, mechanical, electrical, and chemical changes may be made without departing from the spirit or scope of the invention. To avoid detail not necessary to enable those skilled in the art to practice the embodiments described herein, the description may omit certain information known to those skilled in the art. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the illustrative embodiments is defined only by the appended claims.
Unless otherwise specified, any use of any form of the terms “connect,” “engage,” “couple,” “attach,” or any other term describing an interaction between elements is not meant to limit the interaction to direct interaction between the elements and may also include indirect interaction between the elements described. In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to”. Unless otherwise indicated, as used throughout this document, “or” does not require mutual exclusivity.
As used herein, the phrases “hydraulically coupled,” “hydraulically connected,” “in hydraulic communication,” “fluidly coupled,” “fluidly connected,” and “in fluid communication” refer to a form of coupling, connection, or communication related to fluids, and the corresponding flows or pressures associated with these fluids. In some embodiments, a hydraulic coupling, connection, or communication between two components describes components that are associated in such a way that fluid pressure may be transmitted between or among the components. Reference to a fluid coupling, connection, or communication between two components describes components that are associated in such a way that a fluid can flow between or among the components. Hydraulically coupled, connected, or communicating components may include certain arrangements where fluid does not flow between the components, but fluid pressure may nonetheless be transmitted such as via a diaphragm or piston.
An upright beam 15 is rigidly attached to the base 11. In the operating position, the beam is horizontally offset, but approximately parallel with the polished rod 16. Typically, a standard 6 or 8 inch wide-flange I-beam would be used for most shallow well applications. In some embodiments, the beam 15 merely acts as a guide for the traveling head assembly 17 and is not subject to column loading. Light strength material such as aluminum or fiberglass composite can be used instead of steel.
One or more hydraulic cylinders 18 are connected between the base 11 and the head assembly 17. The length of the hydraulic cylinder 18 determines the stroke of the pumping unit. The polished rod load determines the required diameter of the hydraulic cylinder and the system pressure. In some long stroke applications, limitations on the buckling strength of the hydraulic cylinder rod 19 may be design criteria. Typically, a single 4 inch diameter hydraulic cylinder would meet the design criteria for most shallow well applications. Alternately, multiple cylinders can be symmetrically arranged about the beam 15 to provide additional lift capacity.
Energy efficient hydraulic circuits may be employed with the hydraulic pumping units described herein. A charge of compressed gas such as nitrogen may be used in the form of an accumulator to balance the dead weight of the rod string. Another form of energy savings applicable in this and other hydraulic pumping units is to use one or more coil springs 38 to serve the same balancing function as the hydraulic accumulator. In one embodiment, the springs would be sized such that the average hydraulic energy necessary to lift the polished rod 16 on the upstroke is identical, but opposite that required to retract the pump on the down stroke. For example, if the polished rod load is 10,000 lbs. during the upstroke, and the dead weight of the rod string in the well is 5,000 lbs., the springs 38 would be sized to provide an average lifting force of 7,500 lbs. This simple example ignores the difference in force developed on the ring side and cap side of the hydraulic cylinder. In practice, the ideal mechanical spring configuration would attempt to make the hydraulic horsepower equal on both the up stroke and the down stroke.
In contrast to the prior art, a simplified shifting and control system is now presented. As illustrated in
Valve spool 41 is held in place by spring detent assembly 42, illustrated here in prospective view showing only one half of the symmetrically arranged roller bearings that will seat in either the upper detent seat or lower detent seat, each seat corresponding to a respective valve position. The travel of control rod 40 causes shift spring 43 to be compressed until such time there is sufficient force to suddenly unseat detent mechanism. Once unseated, compressed shift spring 43 begins to force valve spool 41 from the present position to the other. Instead of snapping quickly to the alternate valve position, velocity control devices 45, coupled to valve spool 41, dampens the stored energy of the shifting spring 43, thus allowing the valve spool to travel slowly and smoothly from one position to the other. Velocity control device 45 may be an adjustable, variable orifice shock absorber, commercially available to control the velocity of an object being acted upon with an applied force. In a preferred embodiment, the amount of time involved in the shifting process is between 1-5 seconds.
While one embodiment of “soft” mechanical shifting of a hydraulic directional control valve has been described herein, it should be noted that other types of mechanical hydraulic control could provide additional beneficial results. For instance, a valve spool profile can configured so as to provide taper so as to create a variable Cv factor as it travels from one position to the next. In such a case, both valve spool position within the valve body and valve spool geometry can provide non-linear velocity control as the spool changes from one flow path to the other.
In yet another embodiment, two separate valves can be linked to the movement of the hydraulic cylinder stroke such that one valve provides variable flow control, and another separate valve provides directional control. For instance, as the hydraulic cylinder approaches the end of a stroke, a flow control valve begins to progressively reduce the volume rate of fluid flowing to the directional shifting valve. Based on the design of the control valve, the reduction in flow can be in direct or variable relationship to the position of the cylinder with respect to the desired reversal point. An adjustable stop on the flow control valve is used to set a minimum fluid volume rate so as to allow the cylinder to “creep” slowly to the point where direction is reversed. Similar to the function as previously described, a detent used in combination with shifting springs would be used to shift a separate directional control valve. Upon shifting direction, the control valve would progressively open from “creep” for full open position.
The heat exchanger 76, necessary to maintain oil temperature within operating limits, may be of tube and shell construction. In contract to conventional air cooled-radiator type oil coolers, tube-and shell oil coolers can be designed to handle the high operating pressure of the hydraulic system. In one embodiment, fluid pumped from the well may be used as the coolant. As illustrated, heat exchanger 76 is located just prior to the accumulator or tank 80. It is noted that the heat exchanger can be located in most any flow path in the system.
While the embodiments described herein refer to the term “hydraulic” when describing the motive fluid used to raise and lower the cylinders, it should be noted that any type of fluid or mechanical energy could be similarly employed to achieve the same results, including pneumatic sources of energy. For example, an internal combustion engine may be located at or near the location of the pumping unit. In such a case, waste heat from the engine may be converted into steam, either alone or combined with additional input energy. This steam could be used to provide the fluid power necessary to raise and lower the pumping unit. Alternate forms of mechanical linear actuators may also be used to provide the lifting force described herein as that produced by a hydraulic cylinder.
It should be apparent from the foregoing that an invention having significant advantages has been provided. While the invention is shown in only a few of its forms, it is not limited to only these embodiments but is susceptible to various changes and modifications without departing from the spirit thereof.
This application claims the benefit of and priority to U.S. Provisional Application No. 61/875,561, filed Sep. 9, 2013, which is hereby incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61875561 | Sep 2013 | US |
