Abstract:
Methods and systems for removing water from gas wells are described herein. The water is removed by positioning a pump in a liquid layer below the perforations through which gas enters a gas well and powering a water pump with electrical power generated by an energy recovery system which produces electricity from a gas flow through the energy recovery system to an earth surface.

Description:
RELATED APPLICATIONS 
     This invention is entitled to and hereby claims the benefit of the filing date of U.S. provisional patent application 61/067,774 entitled “Downhole Gas Flow Powered Deliquefaction Pump” filed Feb. 29, 2008 by Bryan D. Dotson. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a method and system for removing water from gas wells. The water is removed by positioning a pump in a liquid layer below the perforations through which gas enters the gas well and powering a liquid pump with electrical power generated by an energy recovery system which produces electricity from a gas flow through the energy recovery system to an earth surface. 
     BACKGROUND OF THE INVENTION 
     Many wells which primarily produce gas are also prone to produce liquid in varying quantities with the produced gas. As the gas is produced, the liquid accumulates in the well to a height such that it may well cover the perforations through the well casing into the gas-bearing formation, thereby slowing the production of gas from the well due to the increased hydrostatic head over the outlet from the gas-bearing formation. In some instances the liquid may reach sufficient depths that it substantially stops the production of gas. Such is clearly an undesirable situation. The liquid may be water, oil or mixtures thereof and is referred to herein as “water” or “liquid”. 
     In many instances it has been necessary to position pumps in the well powered by an external source at the surface to remove water from the gas well. This procedure requires additional expense for the installation of the pump and pump motor as well as expense for the electricity required to power the pump and additionally possible expensive maintenance for the pumping equipment. Many such gas wells may be prematurely abandoned due to such expenses when compared to the value of the produced gas. 
     U.S. Pat. No. 4,531,593 issued Jul. 30, 1985 to Guy R. Elliott, et al (Elliott) and entitled “Substantially Self-Powered Fluid Turbines” discloses a system for a self-powered turbine powered by mixtures of gas and liquid with turbines to produce hydrocarbon gases, water vapor, carbon dioxide, other gases and petroleum from watered out wells and from deep or hot wells. This system uses coaxially shaft-coupled turbines which do not provide the capability to run a pump at a necessary and controlled variable speed. 
     It would be highly desirable if a system could be developed to pump the water from the gas well with the pumping being powered by a downhole source which does not reply upon imported electricity but relies instead on power produced within the well to drive the pump. A continuing search has been directed to the development of such equipment. 
     SUMMARY OF THE INVENTION 
     It has now been found that such gas removal can be readily accomplished by a method for removing liquid from a gas well comprising a wellbore extending from an earth surface to penetrate a subterranean gas-bearing formation and a casing positioned in the wellbore, the casing including perforations to permit gas to flow from the subterranean gas-bearing formation into and inside of the casing, the method consisting essentially of: sealingly positioning a packer in the casing above the perforations to sealingly close an inside of the casing; positioning a pump beneath a first liquid surface below the packer in the casing; producing electrical power with an energy recovery system by passing a gas recovered from the subterranean gas-bearing formation at a pressure greater than a pressure at the earth surface through the energy recovery system; powering the pump with the electrical power and operating the pump at a variable rate to maintain the first liquid surface below a first selected level by pumping liquid via a line through the packer to the earth surface; and, providing a liquid drain through the packer and draining liquid from above the packer to maintain a second liquid surface above the packer at a second selected level. 
     The invention further comprises a system for removing water from a gas well comprising a wellbore extending from an earth surface to penetrate a subterranean gas-bearing formation and a casing positioned in the wellbore, the casing including perforations to permit gas to flow from the subterranean gas-bearing formation into an inside of the casing, the system comprising: a packer adapted to sealingly close the inside of the casing above the perforations; an energy recovery system including a passageway sealingly positioned through the packer and adapted to produce electrical energy from gas flowing through the passageway; a pump positioned beneath the packer to pump liquid from the casing beneath the packer through a line sealingly positioned through the packer and in fluid communication with a pump outlet and the earth surface; an electrical connector connecting the energy recovery system and an electric motor positioned to drive the pump; a level controller positioned in operative contact with at least one of the energy recovery system and the pump motor to control the pump to maintain a selected liquid level beneath the packer; and, a drain pipe sealingly positioned through the packer, the drain pipe including a drain pipe level controller to control a liquid level above the packer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The FIGURE is a schematic diagram of an embodiment of the present invention. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     In the FIGURE, a well  10  is shown penetrating a subterranean gas-bearing formation  11  which may produce quantities of liquids, such as water, oil, mixtures of water and oil and the like. The oil may be an oleaginous substance which commonly may be referred to as oil. Well  10  comprises a wellbore  12  which includes a casing  14  cemented in place with cement  16 . The well extends to a bottom  18  of wellbore  12  with the bottom  20  of the casing positioned slightly above bottom  18 . Broken sections  22  and  24  indicate that the well is not to scale, especially with respect to length. 
     Perforations  28  are positioned to provide fluid communication between gas-bearing formation  11  and an inside  26  of casing  14 . As shown, liquid has accumulated in well  10  to a level  30  beneath perforations  28  and a packer  40  which is positioned to sealingly shut-off the inside of casing  14  as shown. A pump  32  is positioned beneath liquid level  30  although pump  32  could be positioned at any level from which suction could be had from the liquid below level  30 . The liquid may be water, brine, crude oil or any other oleaginous fluid. These fluids may be present in any mixture and are equally problematic no matter in what proportions they are mixed. Covering the perforations with fluid is detrimental to the continued production of natural gas from gas-bearing formation  11 . The liquid is pumped by pump  32  powered by a motor  34  through a line  36  to a discharge at the surface as shown by arrow  38 . Line  36  is sealingly positioned through packer  40 . 
     An energy recovery system  41  is shown and includes a passageway  43  through packer  40 . The energy recovery system comprises a generator  42  driven by a fan, turbine, or the like  44 . The fan  44  is housed in a housing  46  which also houses a control system  58  connected with a level control sensor  62  via a line  60 . The level control sensor  62  is adapted to control the level  30  by adjusting the speed of pump  32  by varying the power to pump motor  34  or shutting motor  34  off if required. The control sensor  62  may also be used to adjust the amount of electricity produced by generator  42  by bypassing a portion of the gas passed to fan  44  and upward through passageway  43  to discharge as shown by arrows  52  and  54  upwardly through the inside  22  of casing  14 . A cap  50  is positioned over the top of passageway  43  to prevent liquids, debris and the like from falling into passageway  43 . An exhaust passageway  48  is formed to provide a greater length of passageway  43  to facilitate the passage of gas through energy recovery system  41 . 
     This added height to the energy recovery system enables the maintenance of a liquid layer surface  64  above packer  40 . A drain pipe  66  is sealingly positioned through packer  40  and serves to drain liquid from the liquid layer above packer  40 . It is desirable that a liquid layer be maintained so that gas does not pass through drain pipe  66  rather than through passageway  43 . The liquid level is desirably maintained at a height shown at  65  by the use of a level controller  68 . Drain pipe  66  may comprise simply a one-way valve positioned at a lower end of drain pipe  65  to permit liquid to flow under sufficient pressure to maintain the desired hydrostatic head  65  above packer  40 . Other types of flow controller can be used since a variety of controllers are known to control the depth of a liquid level in a zone controlled by a drain pipe. This results in returning liquid which may be condensed, entrained or otherwise escaped from the area below packer  40  back to the liquid level maintained by pump  32  and motor  34 . Similarly the energy recovery system is sealingly positioned through packer  40 . 
     In the practice of the invention, gas is produced through perforations  28  and liquid level  30  will tend to increase if liquid is produced at a rate high enough to threaten to cover one or more of the perforations without controlled removal. In this instance, the gas which is typically at a pressure greater than the pressure at the earth&#39;s surface, will be produced and passed upwardly through energy recovery system  41  thereby generating electrical power which can be used to power pump  32  and motor  34  to pump the excess liquid from well  10 . 
     When liquid surface  30  has dropped to a desired level, motor  34  may be either shut-off or motor  34  may be reduced to a lesser speed or the like to control the level of liquid in well  10 . This achieved by controllers (not shown) included in controller  58  and motor  34  which are controllable and responsive to level sensor  62 . The liquid level is thus maintained within a defined range by the use of electricity generated downhole so that the well may be produced with no surface power, pumps or the like. 
     The apparatus of the present invention is readily installed by simply assembling the apparatus at the surface and passing it into the well using line  36  to support the assembly for installation at a desired level above perforations  28  so that the pump and motor apparatus are positioned at a suitable distance beneath energy recovery system  41 . The system then operates unattended to effectively enable the efficient production of gas from a gas well with continued removal of liquids as required. 
     The items of equipment needed to construct the apparatus of the present invention are well known and individually available. For instance, the fan  44  may be a turbine, a fan, an axial system or the like. The system is effective to recover energy from the flowing gas stream, as well known to those in the art. This enables the operation of a generator  42  controlled by a controller  58 . The generator may be disengaged partly or entirely to provide either a shut-off or a reduced electric current which will result in a reduced speed at motor  34 . The system is self-controlling based upon the level of liquid in well  10 . The generator may be a centrifugal or axial turbine, sliding vane progressing cavities or the like generator. On such generator which could be adapted to this service is the GT-400 generator, available from Natural Gas Turbine Technologies, Inc. 
     The controls to engage and disengage the generator are considered to be well-known as is the level sensor and the controls to control the speed of motor  34  based upon variations in current. The pump may be a centrifugal pump, a progressing cavity pump, a diaphragm pump, a plunger pump or the like. Such pumps are known for such applications. Similarly, the motor is of a well-known type which can be used to drive any of the types of pumps. 
     The combination of these materials results in a self-regulating system which can operate solely with the energy produced by the gas pressure to maintain a selected liquid level in a gas well. This is a significant improvement in the art and results in the production of natural gas from subterranean formations which also produce liquid at a greatly reduced cost with greatly reduced expense for maintenance, equipment, power and the like. 
     While the present invention has been described by reference to certain of its preferred embodiments, it is pointed out that the embodiments described are illustrative rather than limiting in nature and that many variations and modifications are possible within the scope of the present invention. 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.