Abstract:
A system for lifting liquid from a wellbore includes a turbine selectively coupled to a source of gas flow originating in the wellbore. The turbine is arranged to convert the gas flow directly into rotation of the turbine. An hydraulic pump is rotationally coupled to the turbine. An hydraulic cylinder and piston are arranged to move a sucker rod string disposed in the wellbore. Control valves are provided to selectively apply gas flow to the turbine and hydraulic pressure from the pump to lift the piston and enable lowering thereof by the weight of the sucker rod string. The system further comprises control circuits configured to operate the control valves.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    Not applicable. 
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not applicable. 
       BACKGROUND 
       [0003]    The invention relates generally to the field of removal of liquid from gas producing subsurface wellbores. More particularly, the invention relates to energy sources to operate hydraulic cylinder liquid lifting devices for removal of liquid from such wellbores. 
         [0004]    The oil and gas industry has undergone rapid development in the number of wells drilled for natural gas production from “shale” reservoirs. The number of such gas producing wellbores has increased the need for improved means for deliquification (removal of water) of these wells with typical liquid production rates and depths to as much as 12,000 (can we do 14,000 ft??) feet. 
         [0005]    Hydraulically operated vertical lift cylinders attached to the “wellhead” (control valves and related components at the surface to control fluid flow into and out of the wellbore), like that of electrically or gas engine powered “pump jacks” (reciprocating beam operated sucker rod pumps), provide advantage in many situations due to the incremental stroking of the plunger pump to cause liquids to rise more steadily in a production tubing disposed within the wellbore “casing” (a protective pipe extending to proximate the bottom of the wellbore and typically cemented in place). The action of hydraulic lift cylinders for rod pump well deliquification overcomes a disadvantage common to plunger lift apparatus which tends to release a larger burst of liquid when moved upwardly in the well bore and with such liquid volume comes associated gas. Such large volumes of liquid and gas released in a short time may cause the need for larger separation equipment, and sufficiently large surges of liquid and gas may disturb gas compressor operation. 
         [0006]    Large surges of gas negatively affect compressor intake conditions, control and performance, whereas it can be appreciated that much more attractive and steady flows of both natural gas and liquids are enabled using hydraulic lift cylinder deliquification apparatus. 
         [0007]    It is known in the art to use internal combustion (IC) engines to use a portion of the natural gas being produced from a wellbore to power a conventional beam pump jack. However, this method of producing the well has come under increasing regulatory scrutiny, and more stringent requirements for a well operator to use costly emissions certified IC engines, purchase and maintain IC engine exhaust gas treatment equipment, and costly time-consuming application for and maintenance of air emissions permits has made such wellbore deliquification techniques less attractive economically. In some geographic areas, for example California and the Texas Houston air quality attainment district, increased regulatory scrutiny and likely additional burdens will be placed on oil and gas well operators within a relatively large geographic areas. 
         [0008]    Gas and oil wells tend to decline in production over time, and some even increase liquid (particularly water) production relative to natural gas, natural gas condensate and crude oil, the commonly valued constituents of producing the petroleum well. 
         [0009]    The industry&#39;s commonly accepted threshold limit for producing natural gas and oil wells with the plunger lift method is described, for example, in E. Beauregard, et al., Introduction to Plunger Lift: Applications, Advantages and Limitations, Presented at The Southwestern Petroleum Short Course, Department Of Petroleum Engineering, Texas Tech University, Lubbock, Tex., Apr. 23-24, 1981. As can be appreciated, when the plunger lift method of production will no longer suffice, the oil and gas well operator has previously been faced with having to provide electricity or burn a portion of his produced hydrocarbons in an IC engine to provide the power to operate a sucker rod pump to lift the liquids from the wellbore. 
         [0010]    There exists a need for wellbore deliquification devices that do not require the use of external power sources, such as electricity and/or IC engines. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  shows an example installation of a deliqufication apparatus. 
           [0012]      FIG. 2  shows example hydraulic control circuits for the system of  FIG. 1 . 
           [0013]      FIG. 3  shows a modified form of the example shown in  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    The present invention provides a device and method to be able to produce hydrocarbons from wellbores previously unable to be produced as a result of excessive liquid production in cases where electricity is unavailable or costly to install to the site. Although electricity installation to wellsite would alleviate the air emissions burden, many wells are located either far from electricity access or where grid electricity access is difficult and costly. Since many wells have declined below the ability to naturally flow as a normal progression in mature production decline, large numbers of wells exist where no grid electricity connection has been provided to the wellsite and the costs of installing it are a substantial burden to profitable production of the well. 
         [0015]    The present invention may also provide wellbore operators with the ability to operate a sucker rod pump to remove liquid from wells to maintain and in many cases increase production, with no burning of a portion of produced natural gas, nor any costly, time-consuming requirement to seek regulatory approval for air emissions permit for IC engines, and thereafter the cost and maintenance associated with operating the IC engine to the U.S. Environmental Protection Agency and any state regulatory air emissions standards. 
         [0016]      FIG. 1  shows an example wellbore liquid lift installed on a wellbore. The wellbore terminates at the surface at the upper end of a wellbore casing  22 . A casing head  22 A may be used to seat therein a tubing hanger and production tubing (neither shown in  FIG. 1  for clarity), wherein the production tubing is disposed inside the casing  22 . The casing  22  may include a discharge port and associated control valve, shown at  14 , for venting natural gas pressure that accumulates in annular space between the tubing (not shown) and the wellbore casing  22 . Some of the vented gas may be transferred through a line  19  to processing equipment (not shown in  FIG. 1 ) to separate water to disposal, hydrocarbon liquids for sale and natural gas for eventual compression and transmission to a gas transmission pipeline (not shown). 
         [0017]    Flow and pressure of the gas from the casing  22  may be controlled using a control/regulation valve  16 . The pressure and flow regulated gas may be transferred through a hose or piping  17  to a power conversion unit  12 . The power conversion unit  12  uses flow of natural gas from the wellhead connection (discharge port  14 ) to operate a turbine ( 30  in  FIG. 2 ), the rotation of which may be used to operate an hydraulic pump ( 32  in  FIG. 2 ). The foregoing components will be further explained with reference to  FIG. 2 . The power conversion unit  12  may include control circuitry  12 B including, for example, a microcontroller (not shown separately) to operate the gas control valve  16 , and/or hydraulic valves as will be further explained with reference to  FIG. 2 . Electrical power for the power conversion unit circuitry  12 B may be provided by batteries and/or solar panels  12 A. 
         [0018]    Hydraulic power provided by the power conversion unit  12  may be used to operate an hydraulic lift cylinder  20 . The lift cylinder  20  may be connected to the uppermost portion of the casing  22  with a wellhead connection having an hydraulic oil port, shown generally at  13 . The hydraulic lift cylinder  20  may raise and lower a sucker rod string  20 A. The sucker rod string  20 A may be coupled at its lower end to a conventional wellbore fluid lift pump, including, for example, a standing valve and traveling valve therein (not shown in the figures). During operation, the power conversion unit  12  provides hydraulic pressure to cause the hydraulic cylinder  20  to lift the sucker rod string  20 A. When the sucker rod string  20 A reaches a predetermined upper travel limit, a switch  20 B may operate to send a signal to the control circuitry  12 B to allow controlled dropping of the sucker rod string  20 A within the hydraulic cylinder  20  by release of hydraulic pressure therefrom. 
         [0019]    In other examples (not shown) where desirable, the cylinder  20  could also be mounted at lower portion on a pedestal spaced above the wellhead and coupled to the top of a conventional polished rod; the cylinder/rod coupling would remain above a conventional stuffing box throughout its stroke. An adjustable setting spring over ball backpressure valve is shown at  15 . Such valves are commonly used to hold a backpressure on either the tubing outlet or the casing outlet  14 . Such valve  15  may be used in the present configuration to direct all flow of gas from the casing outlet  14  to the turbine ( 30  in  FIG. 2 ) up to a certain pressure, for example 100 to 150 pounds per square inch. Pressure exceeding the setpoint opens the valve  15  and it then releases the gas being produced by the well in excess of what the turbine needs to go downstream to processing, possible compression and to a pipeline as explained above. 
         [0020]      FIG. 2  shows an example turbine powered hydraulic unit to operate the hydraulic cylinder and sucker rod shown in  FIG. 1 . A turbine  30  is disposed in the flow of gas from the casing  22  as explained with reference to  FIG. 1 . The turbine  30  is rotated by the movement of the gas, and such rotation may be coupled to an hydraulic pump  32  which draws fluid such as hydraulic oil from a reservoir  34 . When it is desired to lift the sucker rod string  20 A, the control circuitry ( 12 B in  FIG. 1 ) may open the control valve  16  to enable turbine rotation and consequent pump  32  rotation, thus pressurizing hydraulic fluid to flow into the hydraulic cylinder  20  to lift the sucker rod string  20 A by applying hydraulic pressure under a piston  20 C connected to the rod string  20 A. When the rod string  20 A reaches the upper limit of its travel, the switch ( 20 B in  FIG. 1 ) may close and cause the circuitry ( 12  in  FIG. 1 ) to close the gas supply control valve  16 . The flow of gas from wellhead casing annulus ceases, as does then turbine rotation and hydraulic pump rotation. A check valve  36  causes the flow of hydraulic oil from out of the cylinder  20  (caused by the weight of the rod string  20 A) to be directed through a controllable orifice valve  38 , which may be manually or otherwise set to enable the rod string  20 A to drop at a practical, optimal descent rate according to the well pumping conditions. In another example, both the controllable orifice valve  38  and the gas supply valve  16  can be configured to be in signal communication with the control circuitry  12 B so that the rate of upstroke lift and downstroke drop of the sucker rod string  20 A may be controlled to optimum benefit, and the control circuitry  12 B may be organized to be in remote communication via any wired or wireless communication technique known in the art. 
         [0021]    Shown at  44  is a pilot operated and adjustable set point ( 46  being the set point adjustment knob) pressure relief valve. Turning the knob  46  changes the spring pressure on the relief valve  44  to obtain a selected relief pressure. By addition of pilot components including an orifice  48  and a pilot valve  42  , the relief valve  44  can also be used to open and let the hydraulic oil return on the downstroke out of the hydraulic cylinder  20  through the relief valve  44  into a filter  50  and ultimately into the supply reservoir  34 . The hydraulic fluid flow is checked at the hydraulic pump  32  outlet (by valve  40 ) to prevent reverse rotation of the hydraulic pump  32 . By further explanation, by re-directing the internal pilot line located upstream of the check valve  40 , the relief valve  44  opens by reduced pressure at the pilot. Hydraulic fluid then returns through the filter  50 . The function occurs due to the position of sourcing pilot pressure port holding the valve  44  closed, (in conjunction with internal pilot valve balance spring) for the duration of time the hydraulic pump  32  operates to lift the sucker rod  20 A. When the upstroke lift has been completed, and the control circuitry  12 B turns off the gas flow to the turbine  30 , the pressure on the pump side of the check valve  40  drops and the relief valve  44  opens, letting returning hydraulic oil out of the cylinder  20  and ultimately into the reservoir  34 . 
         [0022]    The upper portion of the hydraulic cylinder  20  located above the piston  20 C may be filled with hydraulic fluid. The flow of hydraulic fluid out of and into the upper portion may flow through a fluid conduit  20 D in fluid communication with the reservoir  34 . Such configuration may be preferred to accomplish several beneficial functions. The first is to provide for more stable hydraulic oil volume in the reservoir  34 ; this also facilitates minimal reservoir level change in the reservoir  34  from the upstroke to the downstroke. Another possible benefit is minimizing outside air and moisture exchange through a reservoir breather  52 . Further, cooling of the hydraulic oil is facilitated with the cylinder  20  releasing heat from the oil contained therein to the outside air, since in many installations the sucker rod string  20 A can remain in its downward most position and at rest a substantial portion of the time. Any seepage past piston  20 C seals may also be returned to the reservoir  34  because the hydraulic cylinder  20  is hydraulically closed at both ends. The cyclic influx and discharge of hydraulic fluid may clean and lubricate the piston/cylinder interface for longer service life. 
         [0023]      FIG. 3  shows a modified form of the example shown in  FIG. 2 , with the addition of an accumulator arrangement useful for purposes of energy conservation that may be particularly useful when the system is used in deeper wells. The function of the accumulator  60  is to offset, or balance part or all of the sucker rod string lift load. The sucker rod string  20 A may be made, for example, from steel and may weigh approximately 1.5 lbs per foot; thus a 10,000 foot length sucker rod string would weigh approximately 15,000 pounds. In such example a 4.00 inch bore diameter cylinder with a 1.5 inch diameter piston rod coupled to the sucker rod string would require (15,000/10.8) 1389 pounds per square inch pressure applied under the piston  20 C in the hydraulic cylinder  20  to balance the weight of the sucker rod string  20 A of this example. In practice, only a portion of the total hydraulic fluid pressure required to offset the full weight of the sucker rod string  20 A will be used. The particular portion may be chosen according to the particular well conditions, thus to generally maintain a sucker rod string positive weight bias, yet reduce casing head gas and energy consumption by almost half. A piston type accumulator may be preferred, with additional accumulator pressure bottles provided as needed, but the accumulator  60  can also be of the bladder type, where a gas exerts force on hydraulic fluid through a flexible barrier or membrane. The pump  32  receives this hydraulic fluid under pressure to its suction port from the accumulator  60 , reducing the energy required to be exerted by the pump  32  to lift the sucker rod string  20 A. A filter  64  may be used to remove contamination from the hydraulic fluid and may be configured in a manner to prevent contaminants collected therein from being re-entrained when the hydraulic fluid direction through the filter  64  is reversed. Upon completion of sucker rod lift, the relief valve  44  opens to return the hydraulic fluid under pressure to the accumulator  60 , preserving energy for the next sucker rod lift cycle. Pump shaft seal and/or pump case drain hydraulic fluid seepage losses that may result from the pressure imparted by the accumulator  60 , pump and cylinder circuit can be directed to a vent to the reservoir  34  and may be re-introduced to the pressurized hydraulic circuit by a charge pump  62  through a check valve  63 . An adjustable relief valve  61  may mediate the reintroduction of hydraulic fluid according to the relationship of its pressure setting to the lowest point of pressure exerted by the accumulator  60  on the pump  32  intake when the cylinder  20  has lifted the sucker rod  20 A to its highest position. The adjustable relief valve  61  also acts to protect the charging circuit from over-pressure conditions. 
         [0024]    While the example embodiments explained above with reference to  FIGS. 1-3  show the hydraulic cylinder and piston being directly coupled to the sucker rod string, it will be appreciated by those skilled in the art that the above described system could also be used in versions of reciprocating beam pump units (pump jacks) that are operated by selective expansion and contraction of an hydraulic cylinder and piston combination. In still other examples, rotation of the turbine may be converted by devices known in the art to cause reciprocating motion of the beam in such pump jacks, e.g., gearing and rotating pitman arms or cranks. 
         [0025]    A system and method according to the various aspects of the invention may use flow of natural gas out of a wellbore converted directly into mechanical energy to operate a liquid lift pump in the wellbore without the need for external sources of energy, such as electricity, or without the need to consume the gas to release its chemical energy (e.g., by internal combustion or catalytic conversion. 
         [0026]    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.