Beam pumping unit for inclined wellhead

A method and pumping unit for use with an inclined wellhead. Proper address of the wellhead is accomplished through incorporation of an elbow-shaped walking beam. The forward section of the walking beam is fabricated such that its longitudinal axis is angled to address the inclination of the wellhead. The rearward section of the walking beam and the four-bar linkage system remains unchanged relative to a prior art pump jack intended for vertical wells. This modification is a simple and effective means of addressing an angled wellhead while preserving the well-known operating characteristics of a prior art pumping unit. Torque factors, polished rod position, speed, acceleration, stroke length, and effective counterbalance remain unchanged.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to oilfield equipment, and in particular to surface-mounted reciprocating-beam sucker rod pumping units, commonly referred to as pump jacks. More particularly still, the invention relates to pump jacks for producing wells having inclined wellheads.

2. Background Art

Hydrocarbons are often produced from well bores by reciprocating downhole pumps that are driven from the surface by pumping units. A pumping unit is connected to its downhole pump by a rod string. Although several types of pumping units for reciprocating rod strings are known in the art, walking beam style pumps enjoy predominant use due to their simplicity and low maintenance requirements.

FIG. 1shows a class 1 walking beam pump jack (10) of prior art. The pump jack (10) is driven by a prime mover (12), typically an electric motor or internal combustion engine. The rotational power output from the prime mover (12) is typically transmitted by a belt or chain (14) to a gearbox (16). The gearbox (16) provides low-speed high-torque rotation of a crankshaft (22). Each end of the crankshaft (22) (only one is visible inFIG. 1) carries a crank arm (20) and a counterbalance weight (18). The reducer gearbox (16) sits atop a pedestal (17), which provides clearance for the crank arms (20) and counterweights (18) to rotate. The gearbox pedestal (17) is mounted atop a base (11). The base (11) also supports a samson post (13). The top of the samson post (13) acts as a fulcrum that pivotally supports a walking beam (24) via a saddle bearing assembly (15), commonly referred to as a center bearing assembly.

Each crank arm (20) is pivotally connected to a pitman arm (26) by a crank pin bearing assembly (19). The two pitman arms (26) are connected to an equalizer bar (27), and the equalizer bar (27) is pivotally connected to the rear end of the walking beam (24) by an equalizer bearing assembly (25). A horse head (28) with an arcuate forward face (29) is mounted to the forward end of the walking beam (24). The face (29) of the horse head (28) includes one or more tracks or grooves for carrying a flexible wire rope bridle (30). At its lower end, the bridle (30) terminates with a carrier bar (31), upon which a polished rod (32) is suspended. The polished rod (32) extends through a packing gland or stuffing box (34) at the wellhead (9). A rod string (36) of sucker rods hangs from the polished rod (32) within a tubing string (38) located within the well casing (40). The rod string is connected to the plunger of a subsurface pump (not illustrated). In a reciprocating cycle of the pump jack (10), well fluids are lifted within the tubing string (38) during the rod string (36) upstroke.

A walking beam pump jack operates, in essence, as a simple kinematic four-bar linkage mechanism, in which each of four rigid links is pivotally connected to two other of the four links to form a closed polygon. In a four-bar linkage mechanism, one link is typically fixed, with the result that a known position of only one other body is determinative of all other positions in the mechanism. The fixed link is also known as the ground link. The two links connected to the ground link are referred to as grounded links, and the remaining link not directly connected to the fixed ground link is referred to as the coupler link. Four-bar linkages are well known in mechanical engineering disciplines and are used to create a wide variety of motions with just a few simple parts.

Referring toFIG. 1, a four-bar linkage is embodied in the design of the pump jack (10) as follows: A fixed link (Link K) extends from the centerline of the crankshaft (12) to the centerline of the center hearing (15). Link K is defined by a grounded frame formed of interconnected rigid bodies including the samson post (13), the base (11), the gearbox pedestal (17), and the reducer gearbox (16). The first grounded link (Link R) is defined by the crank arms (20), and the second grounded link (Link C) is defined by the rear portion of the walking beam (24) extending from the centerline of the center bearing (15) to the centerline of the equalizer bearing (25). The pitmans (26) and the equalizer (27) together define the coupler link (Link P). This four-bar linkage is dimensioned so as to convert rotational motion of Link R into pivotal oscillation of Link C via the coupler Link P and the fixed Link K. That is, the crank arms (20) seesaw the walking beam (24) about the center bearing (15) atop the samson post (13) via the pitman arms (26) and equalizer (27).

Substantially all of the operating characteristics of a pump jack are determined by the dimensions of its four-bar linkage. For example, the torque factor relationship, polished rod position, stroke length, and counterbalance phase angle are dependent on the four-bar linkage dimensions. Torque factors and counterbalance phase angle are important parameters used to define the load carrying capacity of the pump jack. The varying interaction of these two terms with polished rod position is used to define permissible polished rod load envelope curves that are compared with measured dynamometer load data to verify that the reducer gearbox is operating within the designed torque loading.

The determination of pump jack operating characteristics is greatly simplified by the American Petroleum Institute (“API”) Specification 11E (“Specification for Pumping Units”). API Specification 11E includes derived operational parameters as a function of the geometry of a pumping unit's four-bar linkage, expressed in terms of standardized geometry designations. Accordingly, pump jacks are commonly specified in terms of the API geometry designations, and nearly all pump jack manufacturers provide these API geometry dimensions.

FIGS. 2A and 2Billustrate the geometry designations promulgated by API for class 1 lever and class 3 lever pump jacks, respectively. Dimension “A” is the distance from the center of the saddle bearing to the centerline of the polished rod. Dimension “C” is the distance from the center of the saddle bearing to the center of the equalizer bearing. Dimension “P” is the effective length of the pitman arm as measured from the center of the equalizer bearing to the center of the crank pin bearing. Dimension “R” is the distance from the centerline of the crankshaft to the center of the crank pin bearing. Dimension “H” is the height from the center of the saddle bearing to the bottom of the pump jack base. Dimension “I” is the horizontal distance from the center of the saddle bearing to the centerline of the crankshaft. Dimension “G” is the height from the centerline of the crankshaft to the bottom of the pump jack base. Finally, dimension “K” (FIG. 1) is the distance from the centerline of the crankshaft to the center of the saddle bearing. Dimension “K” may be computed as:
K=√{square root over ((H−G)2+I2)}  (Equation 1).

Pump jacks, like pump jack (10) ofFIG. 1, are typically designed to operate in conjunction with a vertically aligned wellhead (9). However, an increasingly common practice in drilling and production is for the well bore to be inclined at some non-vertical angle so that the well bore penetrates the fluid producing strata along a lengthened path, thus providing the well bore with greater exposure to the producing formation. Directional drilling allows wells to be completed down hole at angles up to and including 90 degrees from vertical.

Depending on the well depth, it may be necessary that the wellhead is also inclined relative to the vertical axis. Such is often the case in shallow wells with near horizontal downhole completion angle or when surface topology prohibits drilling the well from directly above the producing formation. The range of surface inclination typically varies between 0 and 45 degrees from vertical.

Non-vertical wellheads present problems for traditional surface-deployed sucker rod pumping units, because, from both a polished rod load and counterbalance (gravitational) alignment standpoint, pump jack design is based upon a fundamental assumption of vertical operation. This assumption has greatly influenced placement and orientation of structural members, working angles of articulation for the walking beam and horse head, and the phase angle of the crank-mounted counterbalance.

Referring toFIG. 3, U.S. Pat. No. 4,603,592, issued to Seibold et al. (“Seibold”), discloses one potential means of addressing an inclined wellhead with a modified pumping unit (10′) of the class 1 lever type. Seibold teaches adjustably lengthening the pitman arms (26′), tilting the samson post (13′), and enlarging the horse head (28′) so that the pumping unit (10′) can address wellheads (9′) of various inclinations. The effective length of the pitman arm (Link P′) and the rear span (Link C′) of the walking beam are increased to produce the desired angle bias. That is, Seibold approaches the problem of wellhead inclination by altering the four-bar linkage geometry so that the polished rod (32) aligns with the inclined wellhead (9′).

However, because the four-bar linkage is altered, these modifications have a significant effect on the operating characteristics of the pumping unit (10′). Modifications to the pumping unit four-bar linkage generally raise or lower the allowable polished rod load, change the shape of the permissible load envelope, alter the length of the pumping stroke, and induce a phase angle shift in the counterbalance. The polished rod speed and acceleration profiles are also sometimes substantially altered by these modifications.

Moreover, many downstream well analysis programs, diagnostic algorithms, rod pump controllers, and application tools involved in rod pump operation incorporate assumptions based upon standard four-bar linkage (K-R-P-C) usage into their calculations. While it is possible to predict the consequences of a modified linkage (K-R-P′-C′) and make adjustments as per Seibold's recommendations, the end user of the equipment is burdened with a more complex scenario with regard to proper application of the equipment.

Additionally, the prior art Seibold pump jack of FIG.3—with elongated pitman arms walking beam and horse head likely requires more steel than an ordinary pump jack. It is desirable, therefore, to have a pump jack suitable for pumping at inclined wellheads that employs a standard four-bar linkage arrangement.

3. Identification of Objects of the Invention

A primary object of the invention is to provide a method and beam pump apparatus arranged for pumping wells having inclined wellheads in which the four-bar linkage geometry of the pumping unit remains unchanged relative to the standard pumping unit geometry.

Another object of the invention is to provide a method and beam pump apparatus for properly addressing an angled wellhead while leaving the operational characteristics of the pumping unit, the allowable loading envelope, and the motion profile the same as a vertically aligned pumping unit of the same linkage geometry.

Another object of the invention is to provide a method and beam pump apparatus having a modified forward walking beam arranged for pumping wells having inclined wellheads in which torque factors associated with the pumping unit's four-bar linkage are not affected by the modified walking beam.

Another object of the invention is to provide a method and beam pump apparatus for pumping wells having inclined wellheads in which well load is converted to crankshaft torque throughout the pumping cycle at the same rate as with a standard pumping unit design.

Another object of the invention is to provide a method and beam pump apparatus for pumping wells having inclined wellheads in which the polished rod location, speed and acceleration profiles are essentially the same as with the standard vertically aligned pumping unit design.

Another object of the invention is to provide a method and beam pump apparatus having a modified forward walking beam arranged for pumping wells having inclined wellheads in which counterbalance is not affected by the modification and no phase angle mismatch is introduced between the counterbalance torque and well torque curves.

SUMMARY OF THE INVENTION

The objects described above and other advantages and features of the invention are incorporated in a method and apparatus that provides a modified pumping unit for operating in conjunction with a wellhead inclined relative to the vertical. Proper address of the angled wellhead is accomplished through incorporation of a non-linear, or bent, walking beam. The forward section of the walking beam is fabricated such that its longitudinal axis is angled to address the inclination of the wellhead. Specifically, the angled walking beam is shaped such that the bisector of the horse head swept arc, defined by the travel of the horse head during pump operation, is ideally normal to the wellhead axis. The rearward section of the walking beam, from the saddle bearing to the equalizer hearing, and the four-bar linkage system embodied by the pump jack, remains unchanged relative to a prior art pump jack intended for vertical wells.

The samson post is inclined as necessary to maintain proper wellhead clearance and to maintain predominantly compressive reaction forces in the individual samson post members.

Depending on the degree of inclination of the wellhead, the forward samson post members may even be vertical or be inclined forward.

These modification are a simple and effective means of addressing an angled wellhead while preserving the well-known operating characteristics of a prior art pumping unit. Torque factors, polished rod position, speed, acceleration, stroke length, and effective counterbalance remain unchanged.

DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION

Referring toFIG. 4, a preferred embodiment of the invention is a class 1 lever type pumping unit100. Like prior art pump jack10ofFIG. 1, pump jack100includes a prime mover12, typically an electric motor or internal combustion engine. The rotational power output from prime mover12is typically transmitted by a belt or chain14to a gearbox16. Gearbox16provides low-speed high-torque rotation to a crankshaft22. Each end of crankshaft22(only one is visible inFIG. 4) carries a crank arm20and a counterbalance weight18. Reducer gearbox16sits atop a pedestal17, which provides clearance for crank arms20and counterweights18to rotate. The gearbox pedestal17is mounted atop a base11.

Base11supports a samson post13′. The top of samson post13′ acts as a class 1 lever fulcrum that pivotally supports a walking beam24″ via a saddle bearing assembly15(commonly referred to as a center bearing assembly). Each crank arm20is pivotally connected to a pitman arm26by a crank pin bearing assembly19. The two pitman arms26are connected to an equalizer bar27, and equalizer bar27is pivotally connected to the rear end of walking beam24″ by an equalizer bearing assembly25. A horse head28′ with an arcuate forward face29is mounted to the forward end of the walking beam24″. The face29of horse head28′ includes one or more tracks or grooves for carrying a flexible wire rope bridle30. At its lower end, bridle30terminates with a carrier bar31, upon which a polished rod32is suspended. Carrier bar31includes a clamping arrangement to retain polished rod32with limited relative linear movement. Polished rod32extends through a packing gland or stuffing box34at the wellhead9′.

Walking beam24″ is elbow-shaped, which provides for proper address of angled wellhead9′. The elbow shape is formed by a bend or elbow section90that defines forward and rearward sections24A″,24B″, respectively. Bend90is located forward of the centerline of center bearing15. The forward section24A″ of walking beam24″ is fabricated such that its longitudinal axis is angled to address the inclination of the wellhead9′. The radius A from the centerline of center bearing15to the arcuate face29of horse head28′ is tangent to the inclined polished rod32. Ideally, the angled shape of walking beam24″ is such that the bisector52of the horse head swept arc50, defined by the travel of the horse head28′ during pump operation, is ideally normal to the wellhead axis48.

In a preferred embodiment, walking beam24″ is bent downwards, which allows pump jack100to be positioned close to wellhead9′ and allows a shorter bridle30and/or polished rod32. However, if desired, walking beam24″ may be bent upwards (see, e.g.,FIG. 5) to accommodate an inclined wellhead. The rearward section24B″ of walking beam24″ (in particular, rearward of the centerline of center bearing15) and pitman arms26remain unchanged relative to a class 1 lever type pumping unit10(preferably an improved-geometry phased counterbalance model) of prior art intended for vertical wells (FIG. 1). Accordingly, the connected four-bar linkage system is unchanged relative to prior art pump jack10. The non-linear bent walking beam24″ provides a simple and effective means of addressing angled wellhead9′ while preserving the operating characteristics of a prior art pumping unit10(FIG. 1). Torque factors, polished rod position, speed, acceleration, stroke length, and effective counterbalance are essentially unchanged relative to a standard vertical well pumping unit of the same four-bar geometry. And, because neither pitman arms26nor rear walking beam24B″ require elongation to accommodate the inclined wellhead angle, raw material is conserved.

Wellheads9′ of differing angles of inclination generally require fabrication of a bent walking beam24″ that closely matches the wellhead angle. Generally, operators know in advance the wellhead angle and arc able to include such information in the specification to the pumping unit manufacturer. However, an enlarged horse head28′ may be used with pump jack100, as taught by Seibold, so that minor angle variances can be accommodated.

The positioning of the front samson post legs13A in a typical class 1 type pumping unit10(FIG. 1) may interfere with inclined wellhead9′. Moreover, as described by Seibold, the inclined polished rod (well) force may cause undesirable tension forces in a conventionally oriented samson post13. Accordingly, similar to the samson post13′ ofFIG. 3, the forward samson post members13A in pump jack100may have an unusual inclination so that adequate wellhead clearance is maintained. For example, for wellheads having large inclinations, the forward samson post members13A may be inclined forward (i.e., the feet are shifted rearward of the center bearing15). The skewed samson post13′ also allows the direction of the resultant center bearing force to be directed between the front and rear samson post members13A,13B, respectively, ensuring that they are loaded in compression. U.S. Pat. No. 4,603,592, issued to Seibold et al. on Aug. 5, 1986 and entitled “Off-Vertical Pumping Unit,” (“Seibold”), which describes samson post13′, is incorporated herein by reference.

FIG. 5shows an alternate embodiment of the invention—a class 3 lever type pumping unit200. Pump jack200includes a prime mover212, typically an electric motor or internal combustion engine. The rotational power output from prime mover212is typically transmitted by a belt or chain214to a gearbox216. Gearbox216provides low-speed high-torque rotation to a crankshaft222. Each end of crankshaft222(only one is visible inFIG. 5) carries a crank arm220and a counterbalance weight218. Reducer gearbox216sits atop a pedestal217, which provides clearance for crank arms220and counterweights218to rotate. The gearbox pedestal217is mounted atop a base211.

Base211supports a samson post213. The top of samson post213acts as a class 3 lever fulcrum that pivotally supports a walking beam224via a saddle bearing assembly215(commonly referred to as a samson post bearing assembly). Each crank arm220is pivotally connected to a pitman arm226by a crank pin bearing assembly219. The two pitman arms226are connected to an equalizer bar227, and equalizer bar227is pivotally connected near the forward end of walking beam224by an equalizer bearing assembly225. A horse head228with an arcuate forward face229is mounted to the forward end of the walking beam224. The face229of horse head228includes one or more tracks or grooves for carrying a flexible wire rope bridle230. At its lower end, bridle230terminates with a carrier bar231, upon which a polished rod232is suspended. Polished rod232extends through a packing gland or stuffing box234at the wellhead9′.

Walking beam224is elbow-shaped, which provides for proper address of angled wellhead9′. The elbow shape is formed by a bend or elbow section290that defines forward and rearward sections224A,224B, respectively. Bend290is located forward of the centerline of equalizer bearing225. The forward section224A of walking beam224is fabricated such that its longitudinal axis is angled to address the inclination of the wellhead9′. The radius A from the centerline of samson post bearing215to the arcuate face229of horse head228is tangent to the inclined polished rod232. Ideally, the angled shape of walking beam224is such that the bisector252of the horse head swept arc250, defined by the travel of the horse head228during pump operation, is ideally normal to the wellhead axis48.

As shown inFIG. 5, walking beam224may be bent upwards. Walking beam224may also be bent downwards (see, e.g.,FIG. 4). The rearward section224B (in particular, rearward of the centerline of equalizer bearing225) of walking beam224, the pitman arms226, and the four-bar linkage (K″-R″-P″-C″) remain unchanged relative to a prior art class 3 lever type pumping unit. The non-linear bent walking beam224provides a simple and effective means of addressing angled wellhead9′ while preserving the operating characteristics of a prior art pumping class 3 lever type pump jack.

The Abstract of the disclosure is written solely for providing the United States Patent and Trademark Office and the public at large with a way by which to determine quickly from a cursory reading the nature and gist of the technical disclosure, and it represents solely a preferred embodiment and is not indicative of the nature of the invention as a whole.

While some embodiments of the invention have been illustrated in detail, the invention is not limited to the embodiments shown; modifications and adaptations of the above embodiment may occur to those skilled in the art.