Abstract:
Devices and methods for recovering production fluid from a subterranean formation using a mechanical-hydraulic production system. A mechanical-hydraulic production system is described that includes a power fluid pump, a production fluid pump and a hydraulically-actuated motor that is associated with the production fluid pump to actuate the production fluid pump. The power fluid pump is mechanically driven from the surface to fluid hydraulic power fluid to the motor, thereby driving the production fluid pump to pump production fluid.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates generally to systems and methods for operating fluid pumps for subterranean production fluid recovery. 
         [0003]    2. Description of the Related Art 
         [0004]    Enhanced oil recovery techniques often utilize downhole pumps, such as electrical submersible pumps (ESPs) or progressive cavity pumps (PCPs), to increase the flow rate of hydrocarbons from a well. However, it is difficult to use these devices in many lateral or deviated wellbores having tight radius lateral bends. These bends can damage electrical cables and preclude the use of rigid drive rods for operation of the pumps. 
       SUMMARY OF THE INVENTION 
       [0005]    The invention provides devices and methods for the operation of fluid pumps used for recovery of fluids from subterranean formations. The systems and methods of the present invention are particularly suited to operation of fluid pumps in lateral or deviated wellbores. 
         [0006]    An exemplary mechanical-hydraulic pumping system is described that includes a mechanically-actuated power fluid pump that is preferably located within a proximal area of the wellbore and a mechanically-actuated production fluid pump that is preferably located in a distal portion of the wellbore. Mechanical operation of the power fluid pump produces a hydraulic output that is used to power a downhole motor that mechanically drives the production fluid pump. In a described embodiment, flexible power fluid transmission conduits extend between the power fluid pump and the downhole motor and serve to transmit power fluid between the power fluid pump and the downhole motor. In a described embodiment, the power fluid transmission conduits are coaxial. The described transmission conduits also transmit power fluid that has been exhausted by the downhole motor back to the power fluid pump from the motor. Also in a described embodiment, a shroud defines a further fluid transmission conduit that extends between the power fluid pump and the downhole motor to transmit hydrocarbon production fluid from a formation to be produced into production tubing. The production fluid may be transmitted toward the surface via the production tubing. 
         [0007]    In exemplary operation, mechanical power is transmitted from a surface-based mechanical driver, such as a rod drive unit, to the power fluid pump which is preferably located in a proximal portion of a wellbore or other subterranean region. The power fluid pump generates an output of power fluid which drives the downhole motor. The downhole motor mechanically drives the production fluid pump which is preferably located in a distal portion of the wellbore or other subterranean region. In particular embodiments, the proximal portion is a substantially vertical portion of a wellbore while the distal portion is a deviated or lateral portion of the wellbore. 
         [0008]    According to some embodiments of the invention, the exemplary mechanical-hydraulic pumping system includes a fluid accumulator to accommodate thermal expansion/contraction of the power fluid. Also according to some embodiments of the invention, the motor includes a speed increaser which increases the rate of rotation provided by the motor to the production fluid pump. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    For a thorough understanding of the present invention, reference is made to the following detailed description of the preferred embodiments, taken in conjunction with the accompanying drawings, wherein like reference numerals designate like or similar elements throughout the several figures of the drawings and wherein: 
           [0010]      FIG. 1  is a side, cross-sectional view of a wellbore containing an exemplary mechanical-hydraulic pumping system constructed in accordance with the present invention. 
           [0011]      FIG. 2  is a cross-sectional view taken along lines  2 - 2  in  FIG. 1 . 
           [0012]      FIG. 3  is a cross-sectional view of an exemplary accumulator bellows that could be used within the pumping system shown in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0013]      FIG. 1  depicts an exemplary wellbore  10  that has been drilled from the surface  12  down through the earth  14  to a hydrocarbon-bearing formation  16 . The wellbore  10  has a substantially vertical portion  18  and a lateral, deviated portion  20  which are interconnected by angular bend  22 . The substantially vertical portion  18  is proximate the opening  17  at the surface  12  (i.e., a proximal portion of the wellbore  10 ), while the lateral portion  20  is in a distal portion of the wellbore  10 . Perforations  24  extend outward from the lateral portion  20  into the formation  16 . Although perforations  24  are shown in the described embodiment, it will be understood that these are depicted as an example of a wellbore and are not necessary to the invention. The systems and methods of the present invention may be used in open hole wellbores or other wells which do not have perforations. In particular embodiments, at least the substantially vertical portion  18  of the wellbore  10  is lined with casing  19 , of a type well known in the art. Also in particular embodiments, the casing  19  is provided with a gas removal port  21  which permits gas within the casing  19  to escape the casing  19 . 
         [0014]    An exemplary mechanical-hydraulic pumping system, generally indicated at  26 , is disposed within the wellbore  10 . The system  26  includes a mechanically-driven power fluid pump  28  which is disposed within the substantially vertical portion  18  of the wellbore  10 . The power fluid pump  28  includes a lower pump section  30  and an upper seal section  32 , as is known in the art. In one embodiment, the exemplary power fluid pump  28  is actuated by rotation of drive rod  34 . Drive rod  34  extends from the seal section  32  to the surface  12  within production tubing  35  and is rotated at the surface  12  by a mechanical driver in the form of a rod drive unit  36 . In an alternative embodiment, the power fluid pump  28  is actuated by axial reciprocation of rod  34  by the rod drive unit  36 . Suitable pumps for use as the power fluid pump  28  include any of a number of electrical submersible pumps or progressive cavity pumps which are available commercially from Baker Hughes Incorporated of Houston, Tex. In particular embodiments, the rod drive unit  36  is operable to rotate (or axially reciprocate) the rod  34  at variable speeds. 
         [0015]    A production fluid pump, mechanically-actuated fluid pump  38 , is disposed within the lateral portion  20  of the wellbore  10 . The production fluid pump  38  includes fluid intake openings  40  and fluid discharge openings  42 . The production fluid pump  38  may be an ESP or a PCP style pump. Suitable fluid pumps for use as the production fluid pump  38  include a number of ESP or PCP pumps which are available commercially from Baker Hughes Incorporated. A downhole hydraulic motor  44  is affixed to the production fluid pump  38 . The motor  44  uses the power fluid supplied by the power fluid pump  28  to cause rotational energy. In particular embodiments, the motor  44  includes a speed increaser which will increase the rate of rotation that is transmitted from the motor  44  to the second fluid pump  38 . In particular embodiments, the speed increaser of the motor  44  is a gearing arrangement that converts rotation at a lower speed to rotation at a higher speed. A suitable component for use as the speed increaser is a device known in the industry as a gear box. For example, if the power fluid provided by the motor  44  generated a rotational speed of about 500 RPM, the speed increaser might use gears having a ratio of 7:1 to increase the rate of rotation applied to the production fluid pump  38  to 3500 RPM. Suitable motors for use as the hydraulic motor  44  any of a number of motors for driving downhole pumps which are available commercially from Baker Hughes Incorporated. In operation, the hydraulic motor  44  uses hydraulic power fluid as a power input to drive the production fluid pump  38  mechanically. The production fluid pump  38  draws hydrocarbon production fluid into the intake openings  40  and expels the production fluid through the discharge openings  42 . Gas that is within the casing  19  is removed from the casing annulus by gas removal port  21 . Some gas, or substantially all gas, may also be produced through the production fluid pump  38  and through the production tubing  35 , depending upon the application and the selection of pump  38 . 
         [0016]    Flexible hydraulic power fluid conduits  46 ,  48  extend between the power fluid pump  28  and the hydraulic motor  44  that is associated with the production fluid pump  38 . In the embodiment depicted in  FIGS. 1 and 2 , these conduits  46 ,  48  are coaxial. However, in an alternate embodiment, the conduits  46 ,  48  are not coaxial but are, instead, separate, parallel conduits. In the exemplary embodiment, the coaxially inner conduit  46  is a power fluid supply conduit that transmits hydraulic power fluid exiting the first fluid pump  28  to the motor  44 . Also in the exemplary embodiment, the outer coaxial conduit  48  is a power fluid return conduit that returns hydraulic power fluid from the motor  44  to the first fluid pump  28 . 
         [0017]    A flexible shroud  50  radially surrounds the power fluid pump  28 , the hydraulic power fluid conduits  46 ,  48 , the hydraulic motor and speed increaser  44 , and the discharge openings  42  of the production fluid pump  38 . At its proximal end, the shroud  50  is interconnected with the production tubing  35 . At its distal end, the shroud  50  is affixed to the production fluid pump  38 . In particular embodiments, the shroud  50  is formed of resilient steel, polymer or composite material and has sufficient pressure capability and integrity to handle the full discharge pressure of the production fluid pump  38 . 
         [0018]    In operation, the rod drive unit  36  rotates the drive rod  34  to mechanically operate the power fluid pump  28 . In an alternative embodiment, the drive rod  34  is axially reciprocated to operate the power fluid pump  28 . The power fluid pump  28  flows hydraulic power fluid as an output through the power fluid supply conduit  46  to the hydraulic motor and speed increaser  44 . Power fluid that is exhausted by the hydraulic motor and speed increaser  44  is returned to the power fluid pump  28  through the power fluid return conduit  48 . The hydraulic power fluid causes the production fluid pump  38  to draw hydrocarbon production fluid in through the intake openings  40  and expel it through the discharge openings  42 . Expelled hydrocarbon production fluid is flowed through the shroud  50  to production tubing  35 . The production fluid will then flow through the production tubing  35  upwardly toward the surface  12  wherein it will exit the production tubing  35  into production line  52 . 
         [0019]    In particular embodiments, a fluid accumulator  54 , of a type known in the art, is associated with the power fluid conduits  46 ,  48  to accommodate increases and decreases in fluid volume due to thermal expansion and contraction.  FIG. 3  depicts an exemplary fluid accumulator  54  that is incorporated into the production fluid pump  28  below the pump section  30 . The exemplary fluid accumulator  54  includes an outer housing  55  which houses an expandable elastomeric bladder  56  that interconnects with the lower pressure power fluid return conduit  48 . It is noted that the passage of production fluid past the power fluid pump  28  will help to cool the power fluid pump  28  and associated gear box speed increaser. 
         [0020]    The systems and methods of the present invention permit a mechanical drive means at surface  12 , such as rod drive unit  36  to mechanically operate a power fluid pump  28  which, in turn, operates a production fluid pump  38  that is driven by hydraulic power fluid. Thus, the invention provides a power transmission system that can operate efficiently and reliably in deviated wells. Systems constructed in accordance with the present invention are capable of producing hydrocarbon fluid through any reasonable radius lateral bend  22  without conventional concerns relating to side loading of sucker rods or ESP cables being damaged. In addition, the systems and methods of the present invention allow for the intake openings  40  of the second pump  38  to be placed anywhere within the lateral section  20  of the wellbore  10 . 
         [0021]    According to exemplary methods of the present invention, a mechanical-hydraulic pumping system  26  constructed in accordance with the present invention is disposed within the wellbore  10  such that the power fluid pump  28  is located within a proximal portion of the wellbore  10 , and, in particular, the substantially vertical portion  18 . The production fluid pump  38  is disposed within a distal portion of the wellbore  10 , and in particular, the lateral deviated portion  20 . Thereafter, the rod drive unit  36  mechanically drives the power fluid pump  28  via rotation or axial reciprocation of the drive rod  34 . Actuation of the power fluid pump  28  in this manner will flow hydraulic power fluid along the power fluid supply conduit  46  to operate the downhole motor  44 . The motor  44 , in turn, drives the production fluid pump  38  to draw production fluid into the shroud  50 . 
         [0022]    Those of skill in the art will recognize that numerous modifications and changes may be made to the exemplary designs and embodiments described herein and that the invention is limited only by the claims that follow and any equivalents thereof.