Abstract:
Aspects of this invention include a method for deploying a small diameter submersible pump in a deviated wellbore. The submersible pump is first lowered into the production tubing under the influence of gravity. The pump includes a sealing member deployed thereabout which provides a releasable seal with an interior surface of the production tubing. The pump is then forced deeper into the production tubing (e.g., into a deviated section of the wellbore). This is accomplished via introducing a column of liquid (such as water) into the production tubing above the pump. The liquid exerts a force on the pump and sealing member so as to force the pump deeper into the well, thereby drawing one or more power lines into the wellbore with the pump. The invention advantageously enables a small diameter submersible pump to be economically deployed in a highly deviated wellbore. The invention also advantageously enables deployment into partially obstructed and/or damaged tubing.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to downhole submersible pumping systems. More particularly, the invention relates to a method and apparatus for hydraulically installing a submersible pump used in artificial lift applications in hydrocarbon producing wells. 
       BACKGROUND OF THE INVENTION 
       [0002]    Hydrocarbons, and other fluids, are often contained within subterranean formations at elevated pressures. Wells drilled into these formations allow the elevated pressure within the formation to force the fluids to the surface. However, in low pressure formations, or when the formation pressure has diminished, the formation pressure may be insufficient to force the fluids to the surface. In these cases, a pump may be installed to provide the required pressure to produce the fluids. 
         [0003]    The volume of well fluids produced from a low pressure well is often limited, thus limiting the potential income generated by the well. For wells that require pumping systems, the installation and operating costs of these systems often determine whether a pumping system is installed to enable production or the well is abandoned. Among the more significant costs associated with pumping systems are the costs for installing, maintaining, and powering the system. Reducing these costs may allow more wells to be produced economically and increase the efficiency of wells already having pumping systems. 
         [0004]    In recent years, the deployment of small diameter pumps in the production tubing has often provided for economic recovery of well bore fluids. One example of such a small diameter pump is disclosed in commonly invented and commonly assigned U.S. Pat. No. 7,252,148. Commercially available small diameter pumps are commonly powered via hydraulic actuation and are therefore connected to the surface via one or more hydraulic lines. Flexible hydraulic tubing is often preferred due to its low cost. Those of skill in the art will appreciate that electrical and mechanical actuation of downhole pumping systems is also known. 
         [0005]    In service, the production tubing is typically first deployed in a cased wellbore. The small diameter pump is then typically lowered into the well under of the influence of the Earth&#39;s gravitational field. The hydraulic (or electric) power lines are dragged behind until the pump reaches the bottom of the well and is seated in an appropriate connector (e.g., a nipple deployed at the bottom or somewhere along the length of the production tubing). 
         [0006]    Deviated wells are commonly utilized to improve production. Wellbores including vertical, doglegged, and horizontal sections are now common. In such deviated wellbores, deployment of a small diameter pump into the production tubing can be problematic. Gravitational force alone is usually not sufficient to drag the pump around the dogleg or along the horizontal section of the well. To overcome this problem, the pump may be rigidly mounted in the production tubing and forced downhole with the production tubing. However, this results in a “permanent” deployment of the pump and necessitates the removal of the production tubing should the pump fail or merely require routine service. As will be appreciated by those of ordinary skill in the art, such removal of the production tubing is time consuming and therefore expensive. The use of rigid hydraulic lines (or rigid power lines) by which the pump may be forced down the well has also been contemplated. However, rigid hydraulic lines are prone to buckling under compression and are therefore not typically suitable for forcing a pump through a highly deviated section of a wellbore (or through a section having a high dogleg severity). Moreover, this approach adds significant cost to the operation (due to the increased cost of the rigid power lines). 
         [0007]    Therefore, a need remains for a method for deploying a small diameter pump in a deviated borehole and a small diameter pump or small diameter pumping system suitable for such deployment. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention addresses one or more of the above-described drawbacks of the prior art. One aspect of the invention includes a method for deploying a small diameter submersible pump in a deviated wellbore. Methods in accordance with the present invention include at least a two-stage deployment of the pump in the deviated wellbore. In a first stage, the submersible pump is lowered into the production tubing under the influence of gravity. During this first stage the pump is typically supported by at least one power line (e.g., a hydraulic line) that extends from the pump to the surface. The pump includes a sealing member deployed thereabout which provides a releasable seal with an interior surface of the production tubing. In a second stage, the pump is forced deeper into the production tubing (e.g., into a highly deviated section of the wellbore). This is accomplished via introducing a column of liquid (such as water) into the production tubing above the pump. The liquid exerts the necessary force on the pump and sealing member so as to force the pump deeper into the well. The pump preferably includes at least one power line that extends to the surface and is drawn into the wellbore during the first and second stages of the deployment. 
         [0009]    Exemplary embodiments of the present invention advantageously provide several technical advantages. For example, the present invention enables a small diameter submersible pump to be economically deployed in a highly deviated wellbore (e.g., a wellbore including an extended reach horizontal section). The invention also allows the deployment of pumps into tubing that is partially obstructed by solids such as paraffin or scale, and allows pumps to pass by tight spots caused by mechanical tubing damage. Moreover, the invention does not require the use of rigid power lines. Nor is it necessary to mount the pump in the production tubing prior to deployment. The invention also advantageously enables simple and economic removal of the pump from the wellbore. 
         [0010]    In one aspect the present invention includes a method for installing a small diameter submersible pump in production tubing. The method includes providing a length of production tubing deployed in a deviated wellbore, the production tubing including a sealing device deployed therein at a predetermined measured depth. The method further includes providing a small diameter pump having a fluid inlet and a fluid outlet. The pump further includes a sealing member deployed about an outer surface of the pump, the sealing member deployed axially between the fluid inlet and the fluid outlet. At least one power line is coupled to the pump. The pump is lowered into the production tubing with gravitational force drawing the pump into the tubing. The sealing member contacts and provides a releasable seal with an inner surface of the production tubing. The power line extends upward from the pump out an upper end of the production tubing. The method still further includes forcing the pump deeper into the production tubing by introducing a liquid into the production tubing above the pump. The liquid provides a downward force on the sealing member and the pump, the downward force being sufficient to force the pump deeper into the wellbore through a deviated section of the production tubing and into engagement with the sealing device. 
         [0011]    In another aspect, this invention includes a method for installing a small diameter submersible pump in production tubing, the production tubing being deployed in a deviated wellbore. The method includes lowering a small diameter submersible pump into the production tubing, gravitational force drawing the pump into the production tubing. The pump includes a sealing member deployed about an outer surface thereof, the sealing member being deployed axially between a fluid inlet and a fluid outlet. At least one power line is coupled to the pump and extends upward to a surface location. The method further includes forcing the pump deeper into the production tubing by introducing a liquid into the production tubing above the pump. The weight (and/or pressure) of the liquid provides a downward force on the sealing member and the pump, the downward force being sufficient to force the pump deeper into the wellbore and into engagement with a seating nipple deployed in the production tubing. 
         [0012]    In still another aspect, the invention includes a submersible pumping system. The pumping system includes a submersible pump deployed in a length of production tubing, the production tubing deployed in a deviated subterranean wellbore. The submersible pump includes a pump body having a fluid inlet and a fluid outlet. A releasable sealing member is deployed about an outer surface of the pump body axially between the fluid inlet and the fluid outlet. The sealing member contacts and forms a releasable seal with an inner surface of the production tubing. The pump further includes at least one power line connected thereto, the power line extending upwards through the production tubing to a surface location. 
         [0013]    The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: 
           [0015]      FIG. 1  depicts a prior art arrangement in which a submersible pump is deployed in production tubing in a vertical wellbore. 
           [0016]      FIG. 2  depicts one exemplary embodiment of the present invention in flow chart form. 
           [0017]      FIG. 3  depicts a semisubmersible pump partially deployed in a deviated wellbore. 
           [0018]      FIG. 4  depicts the semisubmersible pump depicted on  FIG. 3  fully deployed in the deviated wellbore. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    With reference now to  FIG. 1 , a prior art pumping system  100  includes a small diameter submersible pump  120  operatively connected with surface equipment  150 . The pump  120  is deployed in production tubing  140  in a cased wellbore  32 . The production tubing  140  forms a flowbore that extends upward to surface equipment  150  and carries wellbore fluid from the submersible pump  120  to the surface. Submersible pump  120  is connected to surface equipment  150  via power lines  122 . The surface equipment  150  may include various pumping equipment, valves, piping, power sources, and the like, for example, including a gas-over-liquid scheme to develop the necessary hydraulic pressure needed to drive the submersible pump  120 . 
         [0020]    As is known to those of ordinary skill in the art, the operation of the submersible pump  120  draws wellbore fluid from the wellbore  32  into the pump  120  via a fluid inlet  124 . The fluid is pressurized by the pump  120  and pumped out through fluid outlet  126  to the surface as depicted at  130 . As depicted, pump  120  is engaged with a sealing device  142  (e.g., a seating nipple) deployed at the bottom of the production tubing  140 . Such engagement enables wellbore fluids in the wellbore to enter the pump via inlet  124 . 
         [0021]    In operation, submersible pump  120  may be lowered into the production tubing  140  under the influence of gravity. During this operation, the pump is typically supported by the power lines  122  (e.g., by hydraulic or electrical power lines). The weight of the pump provides the necessary force for the above-described engagement with the sealing device  142 . This practice is well established in vertical (or near vertical) wells. However, in deviated wellbores such gravity assisted deployment can be problematic as the gravitational force is not sufficient to move the pump through the deviated section of the wellbore. Deployment of submersible pumps is particularly problematic in wellbores having horizontal or near horizontal sections (e.g., having an inclination greater than about 75 degrees). 
         [0022]    With reference now to  FIGS. 2 through 4 , one exemplary method embodiment  200  in accordance with the present invention is described in more detail. In  FIG. 2 , the invention is depicted in flowchart form. An exemplary submersible pump  320  in accordance with the present invention is depicted in a deviated wellbore  42  both before ( FIG. 3 ) and after ( FIG. 4 ) step  208  in method  200 . 
         [0023]    At  202 , a length of production tubing  140  is provided in a deviated wellbore  42 . The production tubing  140  includes a sealing device  142  (e.g., a seating nipple) deployed at a predetermined depth in the well (e.g., at the lower end of the tubing as depicted in  FIGS. 3 and 4 ). The production tubing may optionally further include a stripper  148  deployed at the surface for sealingly engaging power line(s) extending upward from a pump. The production tubing typically also includes one or more ports  144  located at the surface. 
         [0024]    A small diameter submersible pump  320  is provided at  204 . The pump  320  includes a fluid inlet  324  and a fluid outlet  326 . The fluid inlet  324  is typically on a lower end of the pump  320  and the fluid outlet  326  on an upper end of the pump  320 , although the invention is not limited in this regard. The pump  320  further includes a sealing member  328  deployed about an outer surface  329  of the pump, the sealing member  328  being located axially between the fluid inlet  324  and outlet  326 . In a preferred embodiment of the invention, the sealing member includes a conventional sand seal, for example, a Flexite® ring available from Harbison-Fisher Mfg. Co., Fort Worth, Tex. At least one power line  322 , e.g., one or more hydraulic lines, is further coupled to an upper end of the pump  320 . 
         [0025]    At  206 , the semisubmersible pump  320  is lowered into the deviated wellbore  42  under the influence of gravity (i.e., gravity draws the pump  320  down into the well). As shown on  FIG. 3 , sealing member  328  contacts an inner surface  145  of the production tubing  140  forming a releasable seal (which may also be referred to as a partial seal) therewith. As the pump  320  is lowered into the well  42 , the power line(s)  322  (e.g., the hydraulic lines) are typically used to support the pump  320  and are drawn down into the well with the pump  320 . In a preferred embodiment of the invention (and as depicted on  FIG. 3 ), the power line(s)  322  may be pulled through a conventional stripper  148 , which is deployed atop the production tubing  140  and which sealingly engages the power line(s)  322 . The pump  320  is typically lowered at step  206  until it can&#39;t be lowered any further by gravitational force alone. As depicted on  FIG. 3 , the pump is often lowered until it reaches a deviated section of the well (e.g., having an inclination greater than about 45 degrees) or a section of the well having a high dogleg severity. 
         [0026]    At  208 , a liquid (preferably water or an aqueous based liquid) is introduced into the production tubing  140  via a port  144  at the surface. The weight of the liquid in the tubing  140  provides a downward force (depicted at  360  on  FIG. 4 ) on the sealing member  328  and on an upper surface of the pump  320  which forces the pump  320  deeper into the well, e.g., through the deviated section of the wellbore  42  and into engagement with the sealing device  142  in the production tubing  140  as depicted on  FIG. 4 . In certain embodiments it may be advantageous to pressurize the liquid so as to increase the downward force  360  on the pump  320 . Such pressurization is sometimes necessary in wellbores  42  having a high dogleg severity section and/or an extended reach horizontal section. Pressurization may also be advantageous when forcing the pump  320  through a mechanically damaged section of the tubing  140 . Notwithstanding, the invention is not limited in these regards as the weight of the liquid alone is often sufficient to force the pump  320  into engagement with the seating nipple  142 . 
         [0027]    As is known to those of ordinary skill in the art, submersible pumps can fail unexpectedly or can simply wear out over time depending on the particular submersible pump and the conditions in the well. This requires removal of the pump from the well since the well ceases to produce once the submersible pump fails. Other reasons for removing the pump from the well are also know (e.g., including a failed installation). Thus, with continued reference to  FIG. 2 , methods in accordance with the invention may optionally further include removing the pump  320  from the wellbore  42 . This may be accomplished, for example, via exerting an upward force on the power line(s)  322  at  210  to disengage the pump  320  from the sealing device  142  (e.g., the seating nipple) and to release (break) the releasable seal between the sealing member  328  and the production tubing  140 . The pump  320  may then be pulled out of the production tubing  140  (and out the well  42 ) by the power line(s)  322  at  212 . 
         [0028]    As described above, the submersible pump  320  is equipped with a sealing member  328  deployed about an outer surface  329  of the pump  320 . Upon deployment of the pump  320  in the wellbore  42 , the sealing member  328  sealingly engages an inner surface  145  of the production tubing  140  (as depicted on  FIGS. 3 and 4 ). In preferred embodiments of the invention, the sealing member  328  forms a releasable seal with the production tubing when deployed therein. By releasable it is meant that the seal between the pump  320  and the production tubing  140  is of moderate strength. On the one hand, the seal must be sufficiently strong so as to support the pressure exerted by the column of liquid in the production tubing at step  208 . On the other hand, it is important that the seal not be so strong as to significantly resist the movement of the pump  320  down into the wellbore (either under the influence of gravity at step  206  or under the influence of the downward force  360  provided at step  208 ). Moreover, it is also important that the seal not be so strong so as to prevent the removal of the pump  320  from the wellbore as described above at steps  210  and  212  ( FIG. 2 ). A seal that is too strong, may render it impossible (or overly difficult) to remove the pump  320  via pulling upward on the power line(s)  322  or may cause the power lines  322  to be damaged during removal of the pump  320 . This can result in the need for expensive fishing operations or in extreme cases, the need to remove the production tubing  140  from the wellbore  42  (if the pump  320  is stuck) or replacement of the power lines  322  ( if they are damaged). It has been found that a hard, self-lubricating, plastic ring (such as a Flexite® ring sand seal available from Harbison-Fischer) provides a seal having a suitable strength for use in embodiments of the present invention. The ring advantageously expands against the production tubing to form the seal between the pump and the tubing. Moreover the ring tends not to swell in service, which advantageously enables the pump to be pulled out of the wellbore. 
         [0029]    In a preferred embodiment of the invention, the pump  320  includes a hydraulically driven diaphragm pump and includes first and second flexible hydraulic lines connected thereto. Preferred embodiments of the pump may employ substantially any known hydraulic actuation mechanism, and may therefore include, for example, one or more pressure intensifiers such as disclosed in commonly invented and commonly assigned U.S. Pat. No. 7,252,148. Furthermore, the pump  320  preferably has a sufficiently small diameter (e.g., less than or equal to 2.5 inch) so as to be deployable in conventional 2⅞ inch production tubing. 
         [0030]    Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alternations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.