Abstract:
Water is removed from a natural gas well using a piston pump is driven by a power fluid that is pumped into the wellbore. The power fluid is intermixed within wellbore water and pumped out of the wellbore along with the removed water.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates generally to devices and methods for removing water from a subterranean wellbore. 
         [0003]    2. Description of the Related Art 
         [0004]    The presence of water is natural gas wells is a significant hindrance to the production of natural gas. Water naturally migrates into a wellbore along with natural gas from the surrounding formation. In the beginning of production, the gas flow rate is high lo enough that it carries the water to surface. As the well matures, the flow rate begins to drop. Eventually, water collects in the wellbore to the point where the production rate becomes very low. In some cases, the weight of the water increases pressure within the wellbore and prevents gas in the surrounding formation from entering the wellbore. 
         [0005]    Prior art approaches to the removal of water from a natural gas well are discussed in U.S. Pat. Nos. 5,211,242; 5,501,279 and 6,629,566. 
       SUMMARY OF THE INVENTION 
       [0006]    The invention provides devices and systems that are useful for removing water from a gas well. In accordance with systems and methods of the present invention, water is removed from a natural gas well using a piston pump is driven by a power fluid that is pumped into the wellbore. An exemplary hydraulic downhole pump is described that is double-acting and double-ended. However, other pump designs may be used, depending upon the depth of the wellbore and the desired output. 
         [0007]    In preferred embodiments, a pilot valve is used to actuate the pump. In the instance where a double-acting downhole pump is used, the cycling valve alternately directs a flow of power fluid into opposing hydraulic chambers in the downhole pump to actuate the downhole pump. 
         [0008]    In preferred embodiments, brine is used as the power fluid for the pump. A surface unit pumps filtered brine down a conduit to the downhole pump. The brine mixes with the produced water and is returned to the surface along with the produced water. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The advantages and further aspects of the invention will be readily appreciated by those of ordinary skill in the art as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference characters designate like or similar elements throughout the several figures of the drawing and wherein: 
           [0010]      FIG. 1  is a side, cross-sectional view of an exemplary natural gas wellbore with a dewatering pump apparatus in accordance with the present invention. 
           [0011]      FIG. 2  is an enlarged, side cross-sectional view of downhole portions of the exemplary pump apparatus shown in  FIG. 1 . 
           [0012]      FIG. 3  is a side cross-sectional view of the pump portions shown in  FIG. 2 , now with the piston member having been shifted to a second position. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0013]      FIG. 1  depicts an exemplary natural gas production wellbore  10  that has been drilled through the earth  12  down to a natural gas-bearing formation  14 . The wellbore  10  has been lined with casing  16 . Perforations  18  extend through the casing  16  and into the formation  14 . A production tubing string  20  extends downwardly into the wellbore  10  and is set into place by one or more packers  22 . An annulus  24  is defined between the production tubing string  20  and the casing  16 . A collection of water  26  is located at the lower end of the wellbore  10 . 
         [0014]    A dewatering apparatus, generally designated at  28  is disposed within the wellbore  10  through the production tubing string  20 . The dewatering device  28  generally includes a downhole hydraulic pump device  30  which has been disposed into the production tubing string  20  by a running string  32 . The running string  32  may be a wireline running string or a string of coiled tubing, as are known in the art. An inflow fluid conduit  34  is incorporated into or disposed along side of the running string  32  and extends from a fluid pump  36 , which is preferably located at the surface  38 , down to the pump device  30 . The pump  36  is operably interconnected with a supply of power fluid  40 . The power fluid  40  is an operating fluid for the downhole pump device  30  and is preferably filtered brine (salt water). A fluid return line  42  extends from the downhole pump  30  to the surface  38  wherein it is preferably associated with a fluid collection point  44 , such as a sump. In some preferred embodiment, a controller  46  is operably associated with the downhole pump  30  via a control line  48 . The controller  46  may be a preprogrammed programmable computer controller, of a type known in the art for actuating the pilot valve  54  of the downhole pump  30  in accordance with a predetermined scheme. In a currently preferred embodiment, the controller  46  operates the pilot valve  54  on a timer. During operation, the fluid pump  36  preferably flows power fluid down through the inflow fluid conduit  34  in a continuous manner. 
         [0015]      FIG. 2  illustrates an exemplary downhole pump  30  in greater detail. The pump device  30  includes a pilot control section  50  and a piston pump portion  52 . It can be seen that the inflow fluid conduit  34  runs into a pilot valve  54  within the control section  50 . A pilot valve is a known device which can be used to control the flow of fluid through the inflow conduit  34  and direct it into either of two chamber conduits  56 ,  58 . An example of a suitable pilot valve for this application is an air-operated directional, four-way, direct acting, spool (4/2) control valve. Pilot valves of this type are available commercially from a number of manufacturers. One such valve suitable for use as the pilot valve  54  is the AODV-12-4A valve available from Command Controls Corporation of Elgin, Ill. In the depicted embodiment, the pilot valve  54  is operably interconnected via control line  48  to the controller  46 . A fluid exhaust line  59  extends from the pilot valve  54  to the fluid return line  42 . 
         [0016]    The pump portion  52  includes an elongated, generally cylindrical housing  60  which defines an interior piston chamber  62 . A piston member  64  is disposed within the piston chamber  62  and is axially moveable therewithin. The piston member  64  includes a central shaft portion  66  with a radially outwardly extending flange  68 . The flange  68  forms a fluid seal against the housing  60  with the preferred assistance of an annular seal ring  70 . The flange  68  divides the piston chamber  62  into upper and lower power chambers  72 ,  74 , respectively. In  FIG. 2 , the piston member  64  is shown in an axially upward position with respect to the housing  60 , and as a result, the volume within the upper chamber  72  is minimized, while the volume of the lower chamber  74  has been maximized. 
         [0017]    The housing  60  of the pump portion  52  as two axial ends  76  and  78 . A tubular sand screen  80 , of a type known in the art for filtering sand and other debris from fluid, is preferably secured to each axial end  76 ,  78 . A first fluid inlet  80  is formed within the upper axial end  76  of the housing  60  to permit fluid communication between the sand screen  80  and the upper power chamber  73 . A one-way check valve  82  is located within the fluid inlet  80  so that fluid may pass into the upper power chamber  73  through the fluid inlet  80 , but cannot exit the upper power chamber  73  via the fluid inlet  80 . 
         [0018]    A second fluid inlet  84  is formed into the lower axial end  78  of the housing  60  to permit fluid communication between the lower sand screen  80  and the lower power chamber  75 . One-way check valve  86  is located within the second fluid inlet  84  to ensure that fluid may pass into the lower power chamber  75  through the fluid inlet  84 , but not exit the lower chamber  75  through the inlet  84 . 
         [0019]    A first fluid outlet  88  is also disposed within or near the upper axial end  76  of the housing  60 . A fluid conduit  90  extends between the fluid outlet  88  and the fluid return line  42 . A one-way check valve  92  is associated with the first fluid outlet  88  so that fluid may exit the upper power chamber  73  via the fluid outlet  88  but not enter the upper power chamber  73  via the fluid outlet  88 . 
         [0020]    A second fluid outlet  94  is formed within or near the lower axial end  78  of the housing  60 . The second fluid outlet  94  is associated with the fluid return line  42  so that fluid may be communicated from the lower fluid chamber  74  and the fluid return line  42 . A one-way check valve  96  is associated with the second fluid outlet  94  so that fluid may exit the lower power chamber  75  via the fluid outlet  94  but not enter the lower power chamber  75  via the fluid outlet  94 . 
         [0021]    In a preferred embodiment, the upper and lower power chambers  73 ,  75  each contain collars  96 ,  98 , respectively. The collars  96 ,  98  function to guide the shaft  66  of the piston member  64  and provide a fluid seal against the shaft  66  preventing power fluid from flowing into chambers  73  or  75 . In addition, the collars  96 ,  98  each include a power fluid inlet  100 ,  102 , respectively, which are formed into the collar  96  or  98 . The first chamber conduit  56  is interconnected via a fluid inlet  96  with the upper power chamber  73 , while the second chamber conduit  58  is interconnected via fluid inlet  102  with the lower power chamber  75 . 
         [0022]    The pump portion  52  is a dual-acting and dual-ended pump. The pump portion  52  is dual-acting in that the pump portion  52  pumps fluid as the piston member  64  is moved axially both in the upward direction and in the downward direction, relative to the housing  60 . The pump portion  52  is dual-ended in that a pumping mechanism is provided at both axial ends  76 ,  78  of the pump portion  52 . 
         [0023]      FIG. 3  depicts the pump  30  now moved from the position shown in  FIG. 2  to a second, stroked position. The pilot valve  54  has flowed fluid through the chamber conduit  56  and into the upper power chamber  73 . Increased fluid pressure bears upon the flange  68  of the piston member  64  to urge it downwardly within the piston chamber  62 . As the piston member  64  moves downwardly, the volume of the upper power chamber  73  is increased while the volume of the lower power chamber  75  is decreased. As power fluid is flowed into the upper power chamber  73  through chamber conduit  56 , power fluid exits the lower power chamber  75  via the chamber conduit  58 . Power fluid exiting the lower chamber  75  via conduit  58  will be returned to the pilot valve  54  and directed by the pilot valve  54  to the fluid return line  42  via exhaust line  59 . Wellbore water within the lower power chamber  75  is pumped toward the surface  38  through the fluid outlet  94 , check valve  96  and fluid return line  42 . As the wellbore water enters the fluid return line  42  it is mixed with the power fluid from the lower power chamber  75 . At the same time, downward movement of the piston member  64  within the piston chamber  62  draws wellbore water into the upper power chamber  73  through the fluid inlet  82 . 
         [0024]    The pump  30  is then operated to move from the position shown in  FIG. 3 , back to the position shown in  FIG. 2 . The pilot valve  54  switches the flow of power fluid from the chamber conduit  56  to the chamber conduit  58 . This causes power fluid to enter the lower power chamber  75  through power fluid inlet  102 . Fluid pressure bears upon the flange  68  of the piston member  64  and urges the piston member  64  axially upwardly within the piston chamber  62 . As the piston member  64  moves upwardly, the shaft  66  displaces wellbore water  26  and power fluid from within the upper power chamber  73 . The displaced wellbore water is flowed through the fluid outlet  82  past check valve  92  and into the fluid return line  42  for return to the fluid collection point  44 . Power fluid within the upper power chamber  73  exits the upper chamber  73  via the chamber conduit  56  to the pilot valve  54  where it is directed via exhaust line  59  to the fluid return line  42 . Once within the return line  42 , the power fluid is mixed with wellbore water. Also, upward movement of the piston member  64  draws wellbore water  26  into the lower power chamber  75  via the fluid inlet  86 . 
         [0025]    As the pilot valve  54  continues to switch fluid flow between the two chamber is conduits  56 ,  58 , the piston member  64  will be alternately moved axially upwardly and downwardly with respect to the housing  60  of the pump portion  52  in a reciprocating manner. Each axial movement of the piston member  64 , or stroke, of the piston member  64 , will result in an amount of wellbore water  26  being flowed upwardly through the fluid return line  42  to the collection point  44 . It is pointed out that, in  FIG. 1 , the supply of operating fluid  40  is shown as separate from the fluid collection point  44 . However, those of skill in the art will understand that the fluid supply  40  and the collection point  44  may be combined. 
         [0026]    As noted, the controller  46  may operate the pilot valve  54  in accordance with a predetermined scheme, and, in a preferred embodiment, the pilot valve  54  is operated according to a time scheme from the controller  46 . In that case, the pilot valve  54  switches fluid flow between the two chamber conduits  56 ,  58  for a particular amount of time that is sufficient to substantially completely shift the piston member  64  within the piston chamber  62 . In an alterative embodiment, the predetermined controller  46  scheme is based upon a substantially complete stroke of the piston member  64  within the piston chamber  62 . A substantially complete stroke would be when the piston member  64  has reached either its furthest upward position or furthest downward axial position with respect to the housing  60 . When the piston member  64  has achieved a substantially complete stroke, the pilot valve  54  will detect a pressure spike within either chamber line  56  or  58 . When the pressure spike is detected, the controller  46  will command the pilot valve  54  to switch the fluid flow between the chamber conduits  56 ,  58  in order to move the piston member  64  in the opposite axial direction with respect to the housing  60 . 
         [0027]    The foregoing description is directed to particular embodiments of the present invention for the purpose of illustration and explanation. It will be apparent, however, to one skilled in the art that many modifications and changes to the embodiment set forth above are possible without departing from the scope and the spirit of the invention.