Abstract:
The present invention generally provides a gas operated pump having a removable and insertable valve. In one aspect, the invention includes a pump housing having a fluid path for pressurized gas and a second fluid path for exhaust gas. The fluid paths are completed when the valve is inserted into a longitudinal bore formed in the housing.

Description:
RELATED APPLICATIONS 
     This application claims benefit of U.S. provisional patent application, Ser. No. 60/239,403, filed Oct. 11, 2000, which is herein incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to artificial lift for hydrocarbon wells. More particularly, the invention relates to gas operated pumps for use in a wellbore. More particularly still, the invention relates to a gas operated pump having a removable valve insertable in a housing with fluid pathways in the housing that operate in conjunction with the valve. 
     2. Description of the Related Art 
     Oil and gas wells include a wellbore formed in the earth to access hydrocarbon-bearing formations. Typically, a borehole is initially formed and thereafter the borehole is lined with steel pipe, or casing in order to prevent cave in and facilitate the isolation of portions of the wellbore. To complete the well, at least one area of the wellbore casing is perforated to form a fluid path for the hydrocarbons to enter the wellbore. In some instances, natural formation pressure is adequate to bring production fluid to the surface for collection. More commonly however, some form of artificial lift is necessary to retrieve the fluid. 
     Artificial lift methods are numerous and include various pumping arrangements. One common pump is a gas operated pump, as shown in FIG.  1 . FIG. 1 is a section view of a wellbore with a gas operated pump disposed therein. The pump  30  is located adjacent perforations in the wellbore  10 . The pump operates with pressured gas injected from a high pressure gas vessel  24  into a gas supply line  80  to a valve assembly  40  disposed in a body of the pump  30 . The valve assembly  40  consists of an injection control valve  70  for controlling the input of gas into a accumulation chamber  34  and a vent control valve  90  for controlling the venting of gas from the chamber  34 . Operational power is brought to the valve assembly  40  by input lines  75 ,  77 . The pump  30  has a first one-way valve  36  at the lower end  38  of the chamber  34 . An aperture  37  at the lower end  38  of the chamber permits formation fluid to flow through open valve  36  to enter the chamber  34 . After the chamber  34  is filled with formation fluid, the vent control valve  90  closes and the injection control valve  70  opens. Gas from the gas supply line  80  is allowed to flow through the open injection control valve  70  into the chamber  34 . As gas enters the chamber  34 , gas pressure forces the formation fluid downward, thereby closing the first one-way valve  36 . As the gas pressure increases, formation fluid therebelow is urged into outlet  42  and opens a second one-way valve  47 . Fluid enters the valve  47  and travels along passageway  32  and into the tubing string  20 . After formation fluid is displaced from the chamber  34 , the injection control valve  70  is closed, thereby restricting the flow of gas from the high pressure gas vessel  24 . 
     Hydrostatic fluid pressure in the passageway  32  acts against second one-way valve  47 , thereby closing the valve  47  and preventing fluid from entering the chamber  34 . The vent control valve  90  is opened to allow gas in the chamber  34  to exit a vent line  100  into an annulus  22  formed between the casing  12  and the tubing string  20 . As the gas vents, the gas pressure decreases thereby reducing the force on the valve  36 . At a point when the formation fluid pressure is greater than the gas pressure in the chamber  34  the valve  36  opens thereby allowing formation fluid to once again fill the chamber  34 . In this manner, a pump cycle is completed. As the gas operated pump  30  continues to cycle, formation fluid gathers in the tubing string  20  and eventually reaches the surface of the well for collection. 
     U.S. Pat. No. 5,806,598 to Mohammad Amani, incorporated herein by reference in its entirety, discloses a method and apparatus for pumping fluids from a producing hydrocarbon formation utilizing a gas operated pump having a valve actuated by a hydraulically actuation mechanism. In one embodiment, a valve assembly is disposed at an end of coiled tubing and may be removed from the pump for replacement. 
     The conventional pumps illustrated in FIG.  1  and described in the &#39;598 patent suffer from problems associated with size limitations in downhole pumps. These valve assemblies for a gas operated pump have an internal bypass passageway for injecting gas into the chamber. The internal bypass passageway must be a large enough diameter to facilitate a correct amount of gas flow into the chamber. These internal structures necessarily make the valve large and bulky. A bulky valve assembly is difficult to insert in a downhole pump because of space limitations in a wellbore and in a pump housing. 
     There is a need, therefore, for a gas operated pump having a valve assembly that is less bulky. There is a further need for a gas operated pump with a removable valve that does not include a bypass passageway. 
     SUMMARY OF THE INVENTION 
     The present invention generally provides a gas operated pump having a removable and insertable valve. In one aspect, the invention includes a pump housing having a fluid path for pressurized gas and a second fluid path for exhaust gas. The fluid paths are completed when the valve is inserted into a longitudinal bore formed in the housing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     So that the manner in which the above embodiments of the present invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings. 
     It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
     FIG. 1 is a cross section view of a prior art gas operated pump assembly in a well. 
     FIG. 2 is a section view showing a housing having a first and second fluid paths formed therein. 
     FIG. 3 illustrates the removable valve assembly disposed on a coiled tubing string. 
     FIG. 4 is a section view showing the removable valve assembly disposed on coiled tubing and located in the bore of the housing. 
     FIG. 5 illustrates another embodiment of a removable valve assembly for a gas operated pump. 
     FIG. 6 illustrates the valve assembly of FIG. 5 in a housing with an alignment tool to install the valve in the housing. 
     FIG. 7 illustrates a removable valve assembly and a housing with an electrical connection means therebetween housing. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 2 is a section view showing a housing  200  of a gas operated pump. In a preferred embodiment, the housing includes two longitudinal bores as well as a number of internally formed motive fluid paths to operate a valve and to direct gas through the pump. The housing  200  includes a first threaded portion  205  formed in an interior of an upper end for connection to a string of tubulars (not shown) and a second threaded portion  210  on the exterior of a lower end for connection to an accumulation chamber (not shown). The housing  200  includes a first longitudinal bore  215  therethrough having an internal threaded portion  220  at a lower end for connection to a diptube (not shown). In use, the bore  215  serves as a conduit for production fluid pumped towards the surface of the well. The housing also includes a second longitudinal bore  225 . An aperture  235  formed in a wall of the housing provides communication between the second longitudinal bore  225  and an exterior of the housing  200 . A third bore  230  provides communication between an injection port  250  in a wall of the second longitudinal bore  225  and a lower end of the housing  200  for injection of pressurized gas into the accumulation chamber (not shown). 
     The second longitudinal bore  225  further includes a first  240  and a second  245  profile formed in an interior of the bore  225  to receive a removable valve assembly (not shown) that is inserted in an upper end  255  of bore  225 . In the preferred embodiment, the profiles  240 ,  245  are continuous grooves and are formed to permit mating formations of the valve assembly to mate therewith as will be more fully described herebelow. 
     FIG. 3 illustrates the removable valve assembly  300  disposed on the end of a coiled tubing string  325 . The removable valve assembly  300  includes an inlet control valve  305 , a vent control valve  310 , a valve stem  315  and an actuator  320 . The valve stem  315  is connected to both the inlet control valve  305  and the vent control valve  310 . The actuator  320  moves the valve stem  315 , alternatively opening and closing the inlet control valve  305  and the vent control valve  310 . When the inlet control valve  305  is in the open position, gas flows down a coiled tubing string  325  into the assembly  300  and out through a gas outlet port  330 . Alternatively, when the vent control valve  310  is in the open position, gas enters a vent inlet port  340  and exits a vent outlet port  335 . A first  345  and a second  350  control conduits are housed inside the coiled tubing string  325 . The first  345  and the second  350  control conduits are typically hydraulic control lines and are used to actuate the valve assembly  300 . Additionally, electric power can be transmitted through the one or more control conduits  345 ,  350  to actuate the valve assembly  300 . Valve assembly  300  may include data transmitting means to transmit data such as pressure and temperature within the pump chamber through the one or more control conduits  345 ,  350  to the surface of the wellbore. In these instances, the valve assembly  300  or the housing  200  may include sensors. Data transmitting means can include fiber optic cable. 
     A first  355 , second  360 , and third  365  seals are circumferentially mounted around an external surface of a valve assembly  300 . The purpose of the seals is to isolate fluid paths between the valve assembly  300  and the housing (FIG. 2) when the valve assembly  300  is inserted therein. The assembly  300  further includes a first  370  and a second  375  key to secure the valve assembly  300  axially within the housing. The first  370  and the second  375  keys are outwardly biased and are designed to mate with the profiles in the interior surface of the housing (FIG.  2 ). 
     FIG. 4 is a section view of the valve assembly  300  disposed in the housing  200 . In the embodiment of FIG. 4, the valve assembly  300  is shown at the end of the string of coiled tubing  325  that provides a source of pressurized gas to operate the pump. An accumulator chamber  415  for collecting formation fluid is secured to the housing  200  by the second threaded portion  210  at the lower end. A tubing string  405  is secured to the housing  200  at the first threaded portion  205 . A diptube  410  is secured to the housing  200  at internal threaded portion  220  of the first longitudinal bore  215 . A vent line  420  is secured to the housing  200  at the aperture  235  to provide a passageway for gas venting from the chamber  415 . 
     In operation, the removable valve assembly  300  is installed at an end of the coiled tubing string  325  and the string  325  is inserted in tubing string  405  at the top of the wellbore. As the valve assembly  300  reaches the housing  200 , a profile means and guide orient and align the valve assembly  300  with the second longitudinal bore  225  which is offset from the center of the housing  200 . Profile means and guides are well known in the art and typically include some mechanical means for orienting a device in a wellbore. After insertion into the upper end  255  of the bore  225 , the valve assembly  300  is urged downwards until the first  370  and the second  375  keys of the valve assembly  300  are secured in place in the first  240  and the second  245  profiles of the housing  200 . Mating angles on the keys and profiles permit the retention of the valve in the housing  200 . The first seal  355  and the second seal  360  form a barrier on the top and bottom of the injection port  250  to prevent leakage of injected gas into the accumulator chamber  415 . The second seal  360  and the third seal  365  provide a barrier on the top and bottom of the aperture  235  to prevent leakage of gas exiting the vent line  420 . 
     FIG. 5 is a section view of an alternative embodiment of a valve assembly  500  and FIG. 6 is a section view of the valve assembly  500  installed in a housing  600 . The housing  600  of FIG. 6 includes additional fluid paths formed therein. Hydraulic conduits  630 ,  635  are formed in the housing  600  and serve to carry hydraulic power fluid from an upper end of the housing  600  to the longitudinal bore  645  formed in the housing  600 . The lines intersect the bore  645  at a location ensuring they will communicate with the valve assembly  500  after it has been installed in the bore  645  and is retained therein with the retention means described with respect to FIG.  4 . Also formed in the housing  600  is an internal gas line  640  providing communication between the upper end of the housing  600  and the bore  645 . 
     By providing hydraulic conduits  630 ,  635  and gas line  640  internally within the housing  600 , there is no need for separate hydraulic lines or a gas supply line to remain attached at an upper end of the valve assembly  500 . As illustrated in FIG. 6, the valve assembly  500  is installed in bore  645  with a selective connector or gripping tool  607  that temporarily retains the valve assembly  500  by gripping a fish neck  580  formed at the upper end of the valve assembly  500 . Gripping tools typically operate mechanically with inwardly movable fingers. A kickover tool can be utilized to align the valve assembly  500  with the offset bore  645 . Kickover tools and gripping tools are well known in the art. Because no rigid conduits are needed between the surface of the well and the upper end of the valve assembly  500 , the assembly  500  can be inserted and removed from the housing using wireline or even slick line. 
     FIG. 7 is a section view of a removable valve assembly  700  in a pump housing  705  with an electrical connection therebetween. For clarity, the assembly  700  is illustrated partially inserted in the housing  705 . In the embodiment of FIG. 7, the housing  705  is electrically wired with conductors  710 ,  715  that lead to a lower portion of the longitudinal bore  720 . A contact seat  725  is located within the bore  720  and is constructed and arranged to receive an electrode  730  protruding from a lower end of the valve assembly  700 . As the assembly  700  is inserted into the bore  720  and is axially located therein, the electrode  730  is seated in the contact seat  725  and an electrical connection between the housing  705  and the valve assembly  700  is made. Thereafter, the valve assembly  700  may be actuated electrically through the use of a solenoid switch  735  disposed within the valve assembly  700 . As with the other embodiments of the invention, the housing includes flow paths formed therein that communicate with the valve assembly  700  and reduce the necessary bulk of the valve assembly  700 . 
     While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.