Abstract:
An electric submersible pump (ESP) torque absorbtion anchor system (TAS) and a method to assemble the same are disclosed. The TAS includes a collar having an uphole end coupled to a production string and a flange formed on an outer diameter of the collar. The TAS also includes a sleeve having a rim extending radially inward from an uphole end of the sleeve. The collar is positioned in a cavity of the sleeve so that oppositely facing shoulders of the collar and the sleeve contact and transfer axial loads between the sleeve and the collar. A spring is positioned in an annulus between the sleeve and the collar and mounts to the collar and the sleeve so that rotational loading of the sleeve relative to the collar transfers to the spring.

Description:
This application claims priority to and the benefit of U.S. Provisional Application No. 61/445,855, by Ghazi-Moradi, et al., filed on Feb. 23, 2011, entitled “TORQUE ABSORBTION ANCHOR SYSTEM,” which application is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates in general to electric submersible pumps and, in particular, to a system to absorb torque generated by electric submersible pump startup and a method to assemble the same. 
     BRIEF DESCRIPTION OF RELATED ART 
     Wells may use an artificial lift system, such as an electric submersible pump (ESP) to lift well fluids to the surface. Where ESPs are used, the ESP may be deployed by connecting the ESP to a downhole end of a tubing string and then run into the well on the end of the tubing string. The ESP may be connected to the tubing string by any suitable manner. In some examples, the ESP connects to the tubing string with a threaded connection so that an uphole end or discharge of the ESP threads onto the downhole end of the tubing string. 
     ESP assemblies generally include a pump portion and a motor portion. Generally, the motor portion is downhole from the pump portion, and a rotatable shaft connects the motor and the pump. The rotatable shaft is usually one or more shafts operationally coupled together. The motor rotates the shaft that, in turn, rotates components within the pump to lift fluid through a production tubing string to the surface. ESP assemblies may also include one or more seal sections coupled to the shaft between the motor and pump. In some embodiments, the seal section connects the motor shaft to the pump intake shaft. Some ESP assemblies include one or more gas separators. The gas separators couple to the shaft at the pump intake and separate gas from the wellbore fluid prior to the entry of the fluid into the pump. 
     The pump portion includes a stack of impellers and diffusers. The impellers and diffusers are alternatingly positioned in the stack so that fluid leaving an impeller will flow into an adjacent diffuser and so on. Generally, the diffusers direct fluid from a radially outward location of the pump back toward the shaft, while the impellers accelerate fluid from an area proximate to the shaft to the radially outward location of the pump. Each impeller and diffuser may be referred to as a pump stage. The shaft couples to the impeller to rotate the impeller within the non-rotating diffuser. In this manner, the stage may pressurize the fluid to lift the fluid through the tubing string to the surface. 
     When ESPs are run into a well, the motor is not operating and must be started following positioning of the ESP at the desired location in the well. In addition, the pump may be selectively started and stopped as necessary to control production from the well. During startup of an ESP motor, a substantial amount of torque is transferred up the tubing string due to the inertia of the motor. This torque can be detrimental to threaded components in the tubing string depending on the horsepower of the motor and the direction of rotation of the system. In embodiments where the tubing string is formed of a weaker material, such as fiberglass, these torsional forces can cause cracking or breaking at coupled joints of the tubular members forming the tubing string. In this manner, the torsional forces generated during motor startup limit the total horsepower of the motor that can be used and, consequently, the overall size of the ESP system. Smaller ESP systems mean that ESPs may not be used in deeper wells having greater pumping heads to overcome. Therefore, a system is needed that can reduce or eliminate the torsional forces generated by motor startup. 
     SUMMARY OF THE INVENTION 
     These and other problems are generally solved or circumvented, and technical advantages are generally achieved, by preferred embodiments of the present invention that provide a torque absorbtion anchor system and method to assemble the same. 
     In accordance with an embodiment of the present invention, an electric submersible pump (ESP) torque absorbtion anchor system is disclosed. The ESP torque absorbtion anchor system includes an annular sleeve having a lower end coupled to an ESP, and an annular collar having a portion coaxially inserted within the sleeve and an uphole coupled to a string of production tubing. The collar and the sleeve define an annulus therebetween. The ESP torque absorbtion anchor system also includes a torsional spring in the annulus that has a portion coupled to the sleeve and another portion coupled to the collar so that when the ESP rotates with respect to the production tubing, the torsional spring is compressed. 
     In accordance with another embodiment of the present invention, an electric submersible pump (ESP) system is disclosed. The ESP system includes a pump to pressurize and lift fluid through a production string, and a motor coupled to the pump so that the motor may operate the pump to pressurize and lift the fluid. The ESP system also includes a torque absorbtion anchor system having a sleeve coupled to a discharge of the pump, a collar coupled to the production string opposite the pump, and a spring connected between the sleeve and the collar. The spring is changeable from a non-compressed configuration to a compressed configuration when the pump rotates with respect to the tubing. 
     In accordance with yet another embodiment of the present invention, a method to assemble a torque absorbtion anchor system coupled between a production string and an electric submersible pump (ESP) is disclosed. The torque absorbtion anchor system is adapted to absorb rotational inertia of the (ESP) during startup of the ESP to prevent transfer of the rotational inertia to the production string. The method provides a collar having an axis and a flange formed proximate to a medial portion thereof, the flange forming an upward and downward facing shoulder, the collar adapted to mount to a production tubing string. The method positions a torsional spring around an outer diameter of the collar so that the torsional spring is axially below the flange and mounts an uphole end of the torsional spring to the collar. The method provides a sleeve having a rim extending radially inward from an upper end of the sleeve to form a downward facing shoulder and inserts the collar into the sleeve so that a downward facing shoulder of the rim of the sleeve rests on an upward facing shoulder of the flange. The method also mounts a lower end of the torsional spring to the sleeve so that when the sleeve rotates relative to the collar, the torsional spring winds and unwinds in response. 
     The disclosed embodiments provide a system that reduces the transfer of rotational inertia or torsional forces up a production string during ESP motor startup. Reducing the transfer of rotational inertia eliminates many of the torsional stresses on coupled joints secured with threaded connections. This, in turn, decreases the risk of early failure of the coupled joints. In addition, removing these torsional stresses permits use of higher horsepower ESP systems and larger ESP systems. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the features, advantages and objects of the invention, as well as others which will become apparent, are attained, and can be understood in more detail, more particular description of the invention briefly summarized above may be had by reference to the embodiments thereof which are illustrated in the appended drawings that form a part of this specification. It is to be noted, however, that the drawings illustrate only a preferred embodiment of the invention and are therefore not to be considered limiting of its scope as the invention may admit to other equally effective embodiments. 
         FIG. 1  is a schematic representation of an electric submersible pump coupled inline to a production string and suspended within a cased wellbore in accordance with an embodiment of the present invention. 
         FIG. 2  is a sectional view of a torque absorbtion anchor system coupling the electric submersible pump and the production string of  FIG. 1  in accordance with an embodiment of the present invention. 
         FIG. 3  is a sectional assembly drawing of the torque absorbtion anchor system of  FIG. 2  in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention will now be described more fully hereinafter with reference to the accompanying drawings which illustrate embodiments of the invention. This invention may, however, be embodied in many different forms and should not be construed as limited to the illustrated embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout, and the prime notation, if used, indicates similar elements in alternative embodiments. 
     In the following discussion, numerous specific details are set forth to provide a thorough understanding of the present invention. However, it will be obvious to those skilled in the art that the present invention may be practiced without such specific details. Additionally, for the most part, details concerning electric submersible pump operation, construction, use, and the like have been omitted inasmuch as such details are not considered necessary to obtain a complete understanding of the present invention, and are considered to be within the skills of persons skilled in the relevant art. 
     The exemplary embodiments of the downhole assembly of the present invention are used in oil and gas wells for producing large volumes of well fluid. As illustrated in  FIG. 1 , downhole assembly  11  has an electrical submersible pump (ESP)  13  with a number of stages of impellers and diffusers. The pump may be driven by a downhole motor  15 , which is a three-phase AC motor. Motor  15  may receive power from a power source (not shown) via power cable  17 . In an embodiment, motor  15  is filled with a dielectric lubricant. A seal section  19  separates motor  15  from ESP  13  and equalizes the internal pressure of the dielectric lubricant within motor  15  to that of a cased wellbore  14  in which ESP  13  is disposed. Additional components may be included, such as a gas separator, a sand separator, and a pressure and temperature measuring module. The devices may couple to the illustrated components to remove gas, remove sand, and monitor fluid pressure and temperature of ESP  13 , respectively. An uphole end of ESP  13  couples to a tubing or production string  21 . 
     ESP  13  couples to a production string  21  through a torque absorbtion anchor system  20 . Production string  21  is formed of one or more tubing string members  18  coupled with joints  16 . In an exemplary embodiment, joints  16  are threaded connections. A person skilled in the art will understand that other couplings may be used to connect tubing string members  18 . Tubing string members  18  and joints  16  may be formed of any suitable material, such as steel, fiberglass, or the like. An uphole end of ESP  13  couples to a downhole end of torque absorbtion anchor system  20 . Similarly, an uphole end of torque absorbtion anchor system  20  couples to a coupler  23  that in turn couples to a downhole end of production string  21 . In this manner, production string  21  supports the axial weight of ESP  13  within wellbore  14  as shown in  FIG. 1 . 
     Referring to  FIG. 2 , production string  21  defines a passageway  22  allowing for the passage of fluids, such as hydrocarbons, uphole. The downhole end of production string  21  is tapered and has a thread formed on an outer diameter of production string  21 . In an exemplary embodiment, the downhole end of production string  21  inserts into coupler  23  and threads to a matching thread on the inner diameter of coupler  23 . In this manner, production string  21  secures to coupler  23  so that production string  21  and coupler  23  are coaxial with an axis  25 . In addition, coupler  23  and production string  21  are non-rotational relative to each other. 
     The torque absorbtion anchor system  20  includes an annular collar  27 , coaxial with axis  25  that has an uphole end with an outer diameter having a thread that mates with a corresponding thread on an inner diameter of a downhole end of coupler  23 . The uphole end of collar  27  inserts into and screws to coupler  23 , securing collar  27  to production string  21 . Similar to production string  21 , collar  27  and coupler  23  are non-rotational relative to each other. Collar  27  includes a flange  26  formed on an outer diameter of a medial portion of collar  27 . Flange  26  has an upward facing shoulder  29  and a downward facing shoulder  28  facing ESP  13  opposite upward facing shoulder  29 . Collar  27  also includes a collar passageway  30  that is coaxial with passageway  22  for passage of fluids, such as hydrocarbons, from ESP  13  through collar  27  to production string  21 . 
     The torque absorbtion anchor system  20  also includes a pump head or sleeve  31  with a rim  32  extending radially inward from the uphole end of sleeve  31 . Rim  32  has a downward facing shoulder  33  on an inner portion of sleeve  31  facing the cavity formed by sleeve  31  and rim  32 . Collar  27  resides within the cavity formed by sleeve  31  and is coaxial with axis  25 . The uphole threaded end of collar  27  extends through and is spaced-apart from an uphole end of sleeve  31 . When collar  27  is positioned within sleeve  31  as shown in  FIG. 2 , shoulder  33  may abut shoulder  29 , so that an upward axial load on collar  27 , such as when ESP  13  must be removed and repaired, will transfer to sleeve  31 . Similarly, a downward axial load on sleeve  31 , such as the weight of ESP  13 , will transfer to collar  27 . In an exemplary embodiment, one or more bearings  35  are interposed between upward facing shoulder  29  of collar  27  and downward facing shoulder  33  of sleeve  31 . Bearings  35  may be rolling element bearings or the like, such that bearings  35  may facilitate rotation of sleeve  31  relative to collar  27  while bearing the axial load between collar  27  and sleeve  31 . In an example, sleeve  31  and collar  27  may rotate independently through bearings  35 . As shown in  FIG. 2 , a seal  36  circumscribes flange  26  axially beneath bearings  35 . Seal  36  substantially fills a gap between flange  26  of collar  27  and an inner diameter of the cavity of sleeve  31 . Seal  36  seals collar  27  to sleeve  31  so that fluid flows through collar passageway  30  into passageway  22  of production tubing  21 . A person skilled in the art will understand that any suitable seal may be used, such as the o-ring seal illustrated in  FIG. 2 . 
     An inner diameter of sleeve  31  is larger than an outer diameter of collar  27  such that an annulus  37  is formed between collar  27  and sleeve  31  axially below flange  26 . A torsional spring  39  is positioned within annulus  37  and surrounds collar  27  in annulus  37 . Collar  27  includes a notch  38  formed proximate to downward facing shoulder  28  of flange  26  so that the uphole end of torsional spring  39  may insert into notch  38  and retain to collar  27 . Notch  38  is of a sufficient size and shape to allow torsional spring  39  to exert a rotational force on notch  38  that will wind and unwind spring  39  without the end inserted into notch  38  slipping out of or becoming dislodged from notch  38 . A downhole end of torsional spring  39  couples to sleeve  31  near a downhole end of sleeve  31  at a slot  40  configured to receive a downhole end of torsional spring  39 . Similar to notch  38  of collar  27 , slot  40  of sleeve  31  will be of sufficient size and shape to allow torsional spring  39  to receive a rotational force from sleeve  31  that will wind and unwind spring  39  without the end inserted into slot  40  slipping out of or becoming dislodged from slot  40 . As sleeve  31  begins to rotate relative to collar  27  due to a torque applied to sleeve  31 , described in more detail below, torsional spring  39  will initially absorb the rotation, maintaining collar  27  stationary by winding around collar  27 . Torsional spring  39  will then unwind as the torque applied to sleeve  31  reaches an equilibrium, returning sleeve  31  to its original position relative to collar  27  prior to the application of the torque to sleeve  31 . 
     In the illustrated embodiment, an alignment bushing  41  is positioned within annulus  37  between the outer diameter of collar  27  and the inner diameter of sleeve  31 . Alignment bushing  41  maintains the downhole ends of sleeve  31  and collar  27  coaxial relative to one another during assembly and operation of torque absorbtion anchor system  20 . As shown, alignment bushing  41  mounts proximate to the downhole ends of collar  27  and sleeve  31 . Alignment bushing  41  may be formed of any suitable material, such as an elastomer, provided alignment bushing  41  permits relative rotation between collar  27  and sleeve  31 . A downhole end of sleeve  31  couples to ESP  13  in any suitable manner such that ESP  13  and sleeve  31  may move axially and rotationally as a single body. In the illustrated embodiment, ESP  13  and sleeve  31  couple through a mating threaded connection. A person skilled in the art will understand that any suitable coupling may be used to couple sleeve  31  to ESP  13 , provided ESP  13  may transfer rotational inertia from ESP  13  to sleeve  31  as described in more detail below. 
     As shown in  FIG. 3 , torque absorbtion anchor system  20  may be assembled as follows. Bearings  35  may be positioned on upward facing shoulder  29  of collar  27 , and torsional spring  39  will be placed around collar  27  so that the uphole end of torsional spring  39  inserts and secures to notch  38  axially beneath flange  26 . Collar  27  may then be inserted into sleeve  31  so that the uphole threaded portion of collar  27  passes through the uphole end of sleeve  31  allowing downward facing shoulder  33  of rim  32  to abut bearings  35  opposite upward facing shoulder  29  of flange  26 . Torsional spring  39  will insert into slot  40  of sleeve  31 , thereby securing the downhole end of torsional spring  39  to sleeve  31 . Coupler  23  is then threaded onto the uphole end of collar  27 . When collar  27  is fully threaded to coupler  23 , a downhole rim of coupler  23  may be proximate to rim  32  of sleeve  31 , providing a barrier to upward axial movement of sleeve  31 . In this manner, coupler  23  may limit axial movement of sleeve  31  by axially securing sleeve  31  to collar  27 , while allowing for independent rotational motion between collar  27  and sleeve  31  at bearings  35 . 
     In operation, during startup of ESP  13 , initial operation of motor  15  generates rotational inertia in ESP  13  that urges ESP  13  to rotate. Rotation of ESP  13  causes sleeve  31  to rotate. Sleeve  31  rotates on bearings  35  relative to collar  27 . In so doing, torsional spring  39 , mounted to a downhole end of sleeve  31 , receives the torsional load through slot  40 , causing torsional spring  39  to wind in response. The uphole end of torsional spring  39  is secured to collar  27  in notch  38 , which remains stationary as torsional spring  39  absorbs the rotational inertia. As the rotational inertia reduces and stabilizes during the startup process of ESP  13 , the reactive forces generated by rotating torsional spring  39  from equilibrium may exert a counter rotational force that overcomes the equalizing rotational inertia of ESP  13 , causing torsional spring  39  to unwind. This rotates sleeve  31  relative to collar  27  in the opposite direction, returning sleeve  31  and ESP  13  to their original positions. In an example, total rotation of ESP  13  and sleeve  31  is less than one revolution. 
     Accordingly, the disclosed embodiments provide numerous advantages. For example, the disclosed embodiments provide a system that reduces the transfer of rotational inertia or torsional forces up a production string during ESP motor startup. Reducing the transfer of rotational inertia eliminates many of the torsional stresses on coupled joints secured with threaded connections. This, in turn, decreases the risk of early failure of the coupled joints. In addition, removing these torsional stresses permits use of higher horsepower ESP systems and larger ESP systems. 
     This application claims priority to and the benefit of co-pending U.S. Provisional Application No. 61/445,855, by Ghazi-Moradi, et al., filed on Feb. 23, 2011, entitled “TORQUE ABSORBTION ANCHOR SYSTEM,” which application is incorporated herein by reference. 
     It is understood that the present invention may take many forms and embodiments. Accordingly, several variations may be made in the foregoing without departing from the spirit or scope of the invention. Having thus described the present invention by reference to certain of its preferred embodiments, it is noted that the embodiments disclosed are illustrative rather than limiting in nature and that a wide range of variations, modifications, changes, and substitutions are contemplated in the foregoing disclosure and, in some instances, some features of the present invention may be employed without a corresponding use of the other features. Many such variations and modifications may be considered obvious and desirable by those skilled in the art based upon a review of the foregoing description of preferred embodiments. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.