Patent Publication Number: US-2013251547-A1

Title: Liquid Lift Pumps for Gas Wells

Description:
BACKGROUND 
     The invention relates generally to the field of downhole pump for use in hydrocarbon producing wells. More specifically, the invention relates to a downhole pump based on displacing water in a chamber where water is trapped using gas pressure, so that the trapped water is pushed toward the surface, for example from gas producing wells unable to transport the water to surface by energy in a hydrocarbon producing, e.g., gas, well. 
     Downhole pumps (i.e., pumps disposed in a wellbore drilled through subsurface formations) used for hydrocarbon production are typically powered either by an electrical cable extending from the surface into the wellbore, or by “sucker” rods connected to a surface drive mechanism. The foregoing types of pumps are typically complicated, have relatively large surface dimensions and can be expensive to install, maintain and retrieve. 
     There exists a need for pumps having smaller surface dimensions, that are less costly to install and maintain and that can also be used to pump oil and water from a wellbore, where the pump can interface directly with preinstalled tubulars (e.g., casing and production tubing in the wellbore. 
     SUMMARY 
     One aspect of the invention is a wellbore liquid lift pump including a pump chamber disposed in a wellbore at a selected longitudinal position and within a liquid column therein. The pump chamber has one way valves proximate each longitudinal end thereof. One of the one way valves is in fluid communication with the liquid column. The other one way valve is in fluid communication with a conduit extending from the pump chamber to the surface. The pump includes means for displacing a volume of the pump chamber by application of pressure thereto. The pressure provided by at least one of a gas and a liquid having a density lower than liquid within the liquid column. 
     A method for lifting liquid out of a wellbore drilled through subsurface formations according to another aspect of the invention includes applying pressure to displace a volume of a chamber disposed in a liquid column in the wellbore. The displacing is constrained to movement of liquid in the chamber in a direction toward the surface. The applying pressure includes at least one of applying gas pressure and applying liquid pressure, wherein the liquid has a density less than water in the water column. The pressure is released to enable water in the water column to enter the chamber. 
     Other aspects and advantages of the invention will be apparent from the description and claims which follow. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a gas well where water trapped therein prevents the gas from a gas producing zone flowing freely into the wellbore and then to the surface. The water needs to be removed to obtain maximum gas production. 
         FIG. 2  illustrates a wellbore where a downhole pump system is placed into the water column. The pump system has a tube attached between the pump and the surface disposed in a production tubing in the wellbore. 
         FIG. 3  illustrates the construction of the downhole pump, where a bladder, inflated by gas or fluids, are placed within a tube area that can be sealed off. 
         FIG. 4A  illustrates the pump system in “relaxed” mode, where water will be located outside the outer tube that the pump is installed within as well as in the area between the pump and the outer tube. 
         FIG. 4B  illustrates that gas, alternative lightweight fluid, (illustrated by red arrows) is pumped in through the center injection line from surface. This gas or fluid inflates the bladder from its lower side, pushing water (illustrated by blue arrows) through the check valves located above the bladder and into the area between the injection line and the tube that the pump is installed within. The check valves below the bladder will close due to increase in pressure of water located between the two check valve systems. 
         FIG. 4C ,  4 D and  4 E illustrates continued inflation of the bladder, pushing more of the trapped water towards surface. 
         FIG. 4F  illustrates that gas or lightweight fluid injection has stopped from surface via the injection line, where a dump valve function located in the outer tube attached nipple or within the pump unit releases the pressurized gas or fluid within the bladder to the area outside the outer tube. Releasing this pressure will cause bladder to collapse due to higher external than internal pressure in the bladder. Upper check valves will close, where these check valves can be spring loaded, while lower check valves will open so that water can enter into the area above the lower check valve system. 
         FIG. 4G  illustrates that bladder is collapsed and that water has entered the area between the upper and lower check valve system. 
         FIG. 5  illustrates a wellbore where a downhole pump system having a steam generator is placed into the water column. The pump system has a tube attached between the pump and the surface. 
         FIG. 6  shows a cross section of a semi-stiff, spoolable rod used to deploy the pump system shown in  FIG. 5 . 
         FIGS. 7A ,  7 B and  7 C illustrate the function of the steam generator. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a wellbore drilled through a gas producing formation  16  in the subsurface. The wellbore may include a pipe or casing  10  therein, and which may be cemented in place in the wellbore. Typically, the casing  10  will include perforations  20  or other fluid permeable devices, such as a screen (not shown) within the axial or longitudinal span of the gas producing formation  16 . Frequently, water  18  may become trapped in the casing  10 . The water  18  may enter the casing  10  from the gas producing formation  16  or other formation that is hydraulically connected to the interior of the casing  10 . Typically, a wellbore will include a production tubing  14  disposed inside the casing  10  and sealed against the interior of the casing  10  using a packer  12  or similar annular seal. The tubing  14  has a smaller diameter than the casing  10  and is used to increase the velocity of the produced gas and water to help entrain the water and lift it to the surface along with the produced gas. The water  18  may become trapped in the casing  10  in certain wellbores because gas entering the casing  10  may not have enough velocity to entrain and lift the water. Trapped water  18  may exert hydrostatic pressure against the gas producing formation  16  and thereby reduce or stop the gas from the gas producing formation  16  flowing freely into the wellbore and then to the surface. The trapped water  18  needs to be removed to obtain maximum gas production. 
       FIG. 2  shows a wellbore having a downhole pump system  26  according to various aspects of the invention disposed in the water  18  in the casing  10 . The pump system  26  may be inserted into the casing  10  through the tubing  14  by extending a tube  24  into the interior of the tubing  14 . The pump system  26  may be coupled to one longitudinal end of the tube  24 . The pump system  26  may be operated to displace the water  18  up the tube  24  to the surface, thereby relieving some of the hydrostatic pressure of the water  18  and enabling gas from the gas producing formation  16  to move to the surface. 
       FIG. 3  illustrates one example of the downhole pump system  26 . In the present example, the pump system  26  may include a pump chamber  37  that may be sealed to the interior of the tubing  14  proximate its longitudinal ends by annular seals  32 ,  32 A. Each annular seal  32 ,  32 A may include a check valve  30 ,  30 A or other type of one way valve, respectively, to enable fluid to enter the chamber  37  from below and move the fluid out of the pump chamber  37  into the tubing  14  above. 
     The pump system  26  may be inserted into the wellbore by using a spoolable tube such as coiled tubing, segmented (jointed) tube or other type of conduit used as the tube  24 . The tube  24  may be connected at its longitudinal end to the pump system  26  by a pressure tight connector  28 . The pump system  26  may include a gas-operated chamber volume displacement element  36 . In the present example, the gas operated chamber volume displacement element  36  may be an elastomer or other type of flexible bladder. Gas pressure applied from the surface into the interior of the tube  24  may be used to inflate the bladder and displace the volume inside the pump chamber  37 . As the volume in the pump chamber  37  is displaced, water in the pump chamber  37  may be moved through the one way valve  30  disposed in the upper annular seal  32 . Water and other fluid in the pump chamber  37  may be prevented from moving downwardly out of the pump chamber  37  by the lower one way valve  32  in the lower annular seal  32 A. 
     The pump system  26  may be installed inside the tubing  14  proximate a longitudinal end thereof, or at any other selected longitudinal position along the tubing  14  by using a nipple  42  threadedly connected within the tubing  14  using, for example, an internally threaded connector  38 . The nipple  42  may include an internal feature having smaller diameter than the internal diameter of the tubing, e.g., a landing shoulder  42 A as shown in  FIG. 3 . 
     If required, for example in highly inclined wells, the pump system  26  can be pumped into the tubing  14  until the pump system  26  lands on the landing shoulder  42 A of the nipple  42 . Fluid pressure applied to the surface end of the tubing  14  will act on the pump chamber  37  by reason of the annular seals  30 A,  32 A. The one way valves  30 ,  32  will seal against such pumping pressure, enabling the pump system  26  to be moved along the interior of the tubing  14  by the force exerted on the annular seals  30 A,  32 A and the pump chamber  37 . 
       FIG. 4A  illustrates the pump system  26  in “relaxed” mode, where water will be located within the tubing  14  as well as in the pump chamber  37 . 
       FIG. 4B  illustrates gas, or alternatively a low density fluid, e.g., kerosene or other liquid having a specific gravity less than that of the water  18 , being pumped in through the tube  24  from the surface. The gas or low density fluid may inflate the bladder (chamber volume displacement element  36 ), thereby pushing the water (illustrated by the arrows) through the upper one way valve  30  located above the chamber volume displacement element  36  and into the annular space  29  between the tube  24  and the tubing  14 . The one way valve  32  below the pump chamber  37  will close due to the increase in pressure of the water in the pump chamber  37  as the chamber volume displacement element  36  is actuated to displace the volume of the pump chamber  37 . 
       FIG. 4C  shows the chamber displacement element  36  continuing to expand, so as to move more of the water disposed in the pump chamber  37  into the annular space  29  between the tube  24  and the tubing  14 .  FIGS. 4D and 4E  illustrate continued expansion of the chamber volume displacement element  36 , pushing more of the water out of the chamber  37  and into the annular space  29  toward the surface. 
       FIG. 4F  illustrates that gas or low density fluid injection has stopped, whereupon a dump valve  44  located in the nipple  42  or within the pump system  26  may release the pressurized gas or fluid within the volume displacement element  36  (e.g., the bladder) to the annular space between the tubing  14  and the wellbore casing  10 . Releasing the pressure in the tube  24  will cause the bladder to collapse due to higher pressure exerted on the bladder. The upper check valve  30  may close, wherein the upper check valve  30  can be spring loaded. The lower check valve  32  will open because the pressure of the water is higher than the pressure in the pump chamber  37 , so that water can enter the pump chamber  37 . The bladder shown in and explained with reference to  FIGS. 4A through 4G  is only one example of a pressure operated chamber volume displacement element. Those skilled in the art will readily recognize that other devices may be used to displace the volume of the pump chamber  37 , for example a piston or bellows operated by gas or liquid pressure applied to the tube  24 . Accordingly, the invention is not limited in scope to the use of an inflatable bladder to displace the volume of the pump chamber. 
       FIG. 4G  illustrates the bladder (pump chamber volume displacement element  36 ) collapsed, and that water has entered and filled the pump chamber  37 . The foregoing process explained with reference to  FIGS. 4A through 4G  may be repeated to continue to lift water out of the wellbore. 
       FIG. 5  illustrates another example of a downhole pump system. In the present example, the pump system may be inserted into the wellbore through the interior of the tubing  14  using a combination semi-stiff, spoolable rod  50 . The semi-stiff spoolable rod (“spoolable rod”)  50  may be made as described, for example in U.S. Pat. No. 5,184,642 issued to Delacour and incorporated herein by reference. A cross-section of the spoolable rod  50  is shown in  FIG. 6  and may include embedded within the rod  50  an electrical cable including insulated electrical conductors  52  and a tube  54 , for example, a stainless steel or other high strength, pressure resistant tube. 
     In the present example, the pump system  26  may be disposed at the end of the spoolable rod  50 , and may be disposed within the wellbore at a selected position along the interior of the tubing ( 14  in  FIG. 5 ) or within the casing ( 10  in  FIG. 5 ) below the annular seal ( 12  in  FIG. 2 ). The present example does not require that the pump system  26  be seated in a nipple in the tubing  14 . The present example pump system  26  may be merely suspended in the wellbore at the end of the spoolable rod  50 . 
     In the present example, and with reference to  FIG. 7A , the chamber volume displacement element may be a steam generator comprising a housing  58  defining a chamber  66  therein. A one way valve may be disposed proximate the bottom of the chamber  66 , shown at  68 , and another one way valve may be disposed proximate the top of the chamber  66 , as shown at  60 . The upper portion of the chamber  66  may be in fluid pressure communication with the tube  54  portion of the spoolable rod ( 50  in  FIG. 5 ) through the upper one way valve  60 . One or more heating elements  62 , e.g., electrical resistance or electrical induction heating elements may be disposed in or around the chamber  66  and may be electrically connected to the electrical conductors  52  in the spoolable rod ( 50  in  FIG. 5 ). The heating elements  62  may include a reflector  64  on their exterior to reflect heat back into the chamber  66 . 
     Referring to  FIG. 7B , when electrical power is applied to the heating elements  64 , water in the chamber  66  may heat to the boiling point, converting the water into steam. The steam may be at a higher pressure than the water it was generated from, and thus cause the upper one way valve  60  to open. The steam may thus travel upwardly inside the tube  54  in the spoolable rod  50 . 
     When the steam pressure is relieved by movement thereof through the upper one way valve  60 , the electric current to the heating elements  64  may be switched off. The gas and steam remaining in the chamber  66  may then be allowed to cool, thus reducing the pressure. As the pressure in the chamber  66  falls below the hydrostatic pressure of the water in the wellbore, and with reference to  FIG. 7C , the water may enter the chamber  66  through the lower one way valve  68 , thus at least partially filling the chamber  66 . The foregoing process as explained with reference to  FIGS. 7A ,  7 B and  7 C may be repeated to continue to remove water from the wellbore. 
       FIG. 7A  illustrates the function of the downhole pump, or steam generator, where the pump system contains the following main components: a fluid intake in the lower end where water will enter the pump chamber  66 ; a spring loaded check valve  68  allowing fluid flow from the intake into the fluid chamber  66 ; and a sealing surface in the lower side of the check valve. The fluid chamber, i.e., steam chamber  66 , is surrounded by a housing that contains heating elements such as for example cables, coils, or similar. A thermal reflection chamber, being for example a thermos construction, a heat reflecting material or similar, can be placed outside the heating elements, but are not crucial for the function of the system. In the upper section of the fluid chamber, a second check valve is mounted, preventing fluids to enter the chamber from the upper side but allowing fluids or steam to escape from the fluid chamber. The upper section of the chamber is connected to a tube wherein the fluids, or steam, exerted from the pump system are pushed to the surface. An electrical cable suspended into the wellbore from the surface will be coupled to the upper section of the pump, where after the electrical conductors are coupled to the heating elements. Those skilled in the art will understand that the check valves here described can be ball types, piston types, or other constructions providing same function. 
       FIG. 7B  illustrates that fluids trapped in the pump chamber will be heated up by the heating elements, which results in an increase in pressure (“Pi”) within this chamber. When this pressure eventually exceeds the pressure in the tube (“Pd”) connected to the pump from the surface, the upper check valve will open causing some of the heated fluids to escape into the tube. When pressure across this valve is equalized, the valve will close. 
       FIG. 7C  illustrates that by switching off the heating elements, the fluids within the fluid chamber will cool down due to the lower temperature fluids externally (“Pe” on  FIG. 3B ) surrounding the pump, resulting in a lower pressure internally in the fluid chamber than the fluids at the fluid intake in the lower end of the pump system. This creates a suction effect within the pump, where cold fluids will enter the fluid chamber via the check valve mounted in the lower section of the pump system. Repeating the heating and cooling of the pump by switching on and off the heating elements, which can be controlled from the surface or built in as an automatic function in the pump system, will continuously evacuate water from a wellbore through the attached tube to surface. 
     The pump system can also be equipped with cooling elements that are electrically powered using the same electrical conductors  52  in the spoolable rod  50  from surface that are used to operate the one or more heating elements  62 . 
     Liquid pumps according to the various aspects of the invention may provide means to lift water and liquids out of a gas producing wellbore to reduce the hydrostatic pressure on gas producing formations without the need to retrofit existing wellbore completion components or without the need for expensive, difficult to install sucker rod pump systems. 
     While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.