Abstract:
A system for producing production fluids from a wellbore while removing gas that collects in pockets within the wellbore. The system includes an electric submergible pumping unit. The unit includes a submergible pump powered by a submergible motor. The fluid discharged by the pump is forced through a pressure reduction device, such as a jet pump, to create a low pressure area. This low pressure area is coupled via a conduit to a gas pocket creation area within the wellbore. For example, gas pockets may develop beneath a packer disposed above the electric submergible pumping system. The low pressure area at the pressure reduction device draws the gas into the discharged production fluid and delivers the mixture to a collection at the earth&#39;s surface.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present invention claims the benefit of provisional patent application No. 60/102,016, filed Sep. 28, 1998, titled, “High Gas Liquid Ratio Electric Submergible Pumping System Utilizing A Jet Pump.” 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to pumping production fluids from a well, and particularly to a system and method that facilitates the pumping of production fluids having a high gas to liquid ratio. 
     BACKGROUND OF THE INVENTION 
     In producing petroleum and other useful fluids from production wells, it is generally known to provide a pumping system for raising the fluids collected in a well. Production fluids enter a wellbore via perforations formed in a well casing adjacent a production formation. Fluids contained in the formation collect in the wellbore and may be raised by the pumping system to a collection point. 
     In an exemplary pumping system, such as a submergible pumping system, the system includes several components. For example, a submergible electric motor is used to power a submergible pump, typically a centrifugal pump. 
     The pumping system is deployed within the wellbore by a deployment system, such as production tubing, through which the production fluids are pumped to the earth&#39;s surface. It is also common practice to set a packer within the wellbore casing. The packer is disposed between the wellbore casing and the deployment system or pumping system components. 
     In certain wells, such as in many offshore oil wells, deep set packers are used to protect the wellbore casing. During production, such wells can produce free gas that accumulates beneath the packer. The gas pocket can continue to grow during pumping. If the gas pocket becomes sufficiently large, it can reach the pump intake and cause slugging to occur in the electric submergible pumping system. To avoid this problem, well operators can maintain a bottom hole pressure above the bubble point of the produced fluid. However, the higher bottom hole pressure reduces the rate of production at these wells. 
     Attempts have been made to remove the gas, while maintaining higher production rates. For example, coil tubing can be used to vent the gas from beneath the packer to the surface. However, such methods substantially complicate the completion, e.g. electric submergible pumping system. 
     SUMMARY OF THE INVENTION 
     A system is provided for producing production fluids from a wellbore. The system is comprised of an electric submergible pumping system that includes at least one submergible pump, at least one pressure reduction device, at least one intake disposed to draw liquid, and at least one secondary intake coupled to the at least one pressure reduction device. The at least one pressure reduction device is powered by the at least one submergible pump and draws a gas from the wellbore through the at least one secondary intake. 
     According to another aspect of the invention, a system is provided for removing free gas from a wellbore. The system is comprised of: a submergible pump; a pressure reduction device through which the submergible pump forces a flow of wellbore fluid; a gas inlet coupled to the pressure reduction device and disposed within the wellbore at a gas pocket formation region; and source of power for the pump. 
     According to another aspect of the invention, a method is provided of producing fluids and removing free gas from a wellbore. The method is comprised of locating a submergible pump in a wellbore and powering the submergible pump with a submergible motor. The method further includes discharging wellbore fluid flow from the submergible pump through a pressure reduction device to create a low pressure area. The method further includes coupling the low pressure area with a gas formation area disposed in the wellbore. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements, and: 
     FIG. 1 is a front elevational view of an electric submergible pumping system positioned in a wellbore, according to a preferred embodiment of the present invention; 
     FIG. 2 is a cross-sectional view of a jet pump used with the system of FIG. 1, according to a preferred embodiment of the present invention; 
     FIG. 3 is a front elevational view of an alternate embodiment of the system illustrated in FIG. 1; 
     FIG. 4 is a cross-sectional view of the jet pump illustrated in FIG. 3; and 
     FIG. 5 is a front elevational view of a jet pump system, according to an alternate embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Generally, the present invention relates to methods and systems that utilize a jet pump in novel fashion to facilitate pumping of liquids with a high gas to liquid ratio. Centrifugal pumps commonly are used in downhole environments to pump production fluids. However, it is undesirable and potentially damaging to permit bubbles or pockets of gas in high gas to liquid ratio fluids to be pumped through the centrifugal pump. Accordingly, the bubbled gas or at least a portion of the gas should be removed from the production fluid prior to entering the centrifugal pump. However, the released gas can collect in the wellbore and cause further problems, as discussed above. Also, even without removing gas from the production fluid, a gas pocket can form beneath the packer and present problems for the pumping system. According to the present invention, pump, e.g. a jet pump can be driven by the produced fluid stream and utilized to remove the gas from the wellbore and introduce it into the produced fluid stream above the initial centrifugal pump. 
     Referring generally to FIG. 1, a first preferred embodiment of the present invention is illustrated. In this embodiment, a pumping system  10  is designed for deployment in a well  12  within a geological formation  14  containing desirable production fluids, such as petroleum. In a typical application, a wellbore  16  is drilled and lined with a wellbore casing  18 . Pumping system  10  is deployed within wellbore  16  by a deployment system  20 , such as production tubing  22 . 
     A packer  24  is disposed between production tubing  22  and wellbore casing  18 . In this environment, packer  24  is disposed above pumping system  10  to protect wellbore casing  18 . 
     Pumping system  10  preferably includes a submergible motor  26  for driving a submergible pump  28 , such as a centrifugal pump. Connected between motor  26  and pump  28  is a motor protector  30  and an intake  32  disposed between motor production  30  and pump  28 . Often, intake  32  comprises a gas separator. In either case, intake or gas separator  32  includes intake openings  34  through which fluid enters pumping system  10  from wellbore  16 . Optionally, an advanced gas handling system  36  may be disposed between intake  32  and pump  28  to further reduce any bubbles of gas contained in the production fluid. A preferred system  36  is the Advanced Gas Handling System available from Reda of Bartlesville, Okla., a Camco International Company. 
     A pump  38 , such as a jet pump, is disposed above pump  28 . Additionally, a second submergible pump  40 , such as a centrifugal pump, is disposed above jet pump  38  in the string of components of pumping system  10 . Optionally, a second advanced gas handling system  42  may be disposed between jet pump  38  and second submergible pump  40 . A conduit  44  is connected to jet pump  38  and extends upwardly towards packer  24 . Conduit  44  includes an inlet  46  disposed towards packer  24  for communication with any gas pockets that form beneath packer  24 . 
     During operation of pumping system  10 , a fluid  48  disposed in wellbore  16  naturally may be at a pressure that is below the bubble point pressure of the fluid. Thus, gas bubbles can be formed. This gas preferably is removed by gas separator  32 . Gas expelled from, for example, gas separator  32  is forced into the annulus between pumping system  10  and wellbore casing  18 . The naturally occurring gas and any expelled gas rises upwardly until it is trapped beneath packer  24  forming a gas pocket SO. 
     Gas pocket  50  is reduced and controlled by pulling gas back into the production stream via jet pump  38  and conduit  44 . When the gas is reintroduced into the production stream at jet pump  38 , the production fluid preferably is maintained at a pressure above the bubble point. Thus, bubbles and/or gas pockets do not form in the production stream, and submergible pump  40  is readily able to pump the produced fluid up production tubing  22  to the earth&#39;s surface. Maintenance of the an internal pressure above the bubble point pressure of the produced fluid at the jet pump  38  does not substantially effect the rate at which the fluid may be produced. 
     In the illustrated system, submergible pump  28  effectively acts as a charge pump for powering jet pump  38 . Pump  28  is sized and designed to pump at the desired liquid rate through the jet pump to maintain performance of the jet pump  38 . The second submergible pump  40  effectively acts as the production pump able to pump the production fluid and entrained gas to the surface. The mixture is maintained at sufficiently high pressure to avoid formation of bubbles in pump  40 . 
     A preferred embodiment of jet pump  38  is illustrated in FIG.  2 . Jet pump  38  includes an external housing  52  having a lower mounting end  54  and an upper mounting end  56 . A shaft  58  is rotatably mounted within and extends through housing  52  and mounting ends  54  and  56 . Shaft  58  is part of several shaft portions connected from motor  26  through the various components to power, for instance, centrifugal pumps  28  and  40 . 
     At least one and preferably a plurality of jet pump nozzle  60  are disposed about shaft  58  within housing  52 . Jet pump  38  has a fluid inlet  62  disposed through mounting end  54 . Fluid flows through inlet  62  along a fluid corridor  64  to an interior cavity  66  of each jet pump nozzle  60 . Each jet pump nozzle  60  also includes a narrow outlet or orifice  68  in fluid communication with internal cavity  66 . 
     The cross-sectional area of each orifice  68  is smaller than the largest cross-sectional area of each jet pump nozzle  60 . As fluid flows through inlet  62  and fluid corridor  64 , it creates a static head (P 1 ) in internal cavity  66 . As this fluid is forced through orifice  68  of each nozzle  60 , the velocity of flow is increased, thereby creating a low-pressure area (P 2 ) at the discharge of each jet pump nozzle  60 . 
     Conduit  44  is connected to jet pump  38  at an inlet  70 . Inlet  70  is disposed externally of jet pump nozzle or nozzles  60  proximate the area of discharge of fluid through orifice  68 . Thus, the liquid flowing through orifice  68  must be of a velocity that will sufficiently lower the pressure at P 2  to permit the gas in gas pocket  50  to be forced through conduit  44  and opening  70  into combination with the fluid discharged through orifice  68 . 
     The gas and fluid are mixed in a throat region  72  of jet pump  38 . The mixture of fluid and gas flows through throat region  72  and into the expanded diffuser region  74 . Preferably, the pressure (P 3 ) in diffuser region  74  is higher than the downhole pressure external to pumping system  10 . Most preferably, the pressure P 3  is maintained higher than the bubble point pressure of the mixture of fluid from orifice  68  and gas from inlet  70 . This higher pressure prevents formation of bubbles as the mixture is moved through second submergible pump  40 . In some design applications, it may be desirable to maintain pressure P 3  below the bubble point pressure of the mixture. In this situation, however, it may be necessary to utilize an advanced gas handling system  42  to limit the gas bubbles and pockets flowing into pump  40 . Thus, as the gas and liquid mixture exits diffuser  74  through an outlet  76 , it enters second submergible pump  40  either directly or through advanced gas handling system  42 . 
     Referring generally to FIG. 3, an alternate embodiment of pumping system  10  is illustrated. In this embodiment, Pumping system  10  includes a submergible motor  80  connected to a submergible pump  82 , such as a centrifugal pump. Disposed between motor  80  and pump  82  may be a motor protector  84  and a fluid intake  86 . The fluid intake may comprise a gas separator. Additionally, pumping system  10  includes a jet pump  88  disposed between pump  82  and packer  24 . An exemplary jet pump  88  is a wireline retrievable jet pump designed for placement at a specific location within production tubing  22 . Jet pump  88  has a gas inlet  90  through which gas is pulled from wellbore  16  beneath packer  24 . If jet pump  88  is a wireline retrievable jet pump disposed within production tubing  22 , inlet  90  must be aligned with corresponding openings  92  through production tubing  22 . 
     In operation, motor  12  drives pump  82  which, in turn, intakes production fluid from wellbore  16  and discharges it upwardly into production tubing  22 . The discharge of pump  82  is flowed through jet pump  88  to create suction at inlet  90 . This suction removes gas accumulated beneath packer  24  and causes it to be entrained in the produced fluid stream pumped to the earth&#39;s surface through production tubing  22 . 
     A preferred embodiment of jet pump  88  is illustrated in FIG.  4 . As shown, the fluid discharged from pump  82  flows into a jet pump nozzle  94 . Then, the fluid is discharged from nozzle  94  through a narrower orifice  96 . As the fluid is forced through narrower orifice  96 , its velocity is increased, thereby causing a low pressure area  98  at the point of discharge. Low pressure area  98  allows gas from wellbore  16 , collected beneath packer  24 , to be forced through openings  92  and inlet  90  into low pressure area  98 . The fluid flowing through orifice  96  and the gas flowing into low pressure area  98  are mixed at a throat area  100  which maintains a relatively high velocity of the fluid/gas mixture. After the mixture flows through throat  100  it moves into an expanded diffuser region  102  and exits jet pump  88  through an outlet  104  for continued flow through production tubing  22 . 
     In the illustrated embodiment, jet pump  88  preferably includes a latch mechanism  106 . Latch mechanism  106  maintains jet pump  88  at a specific, desired location within production tubing  22 . Additionally, jet pump  88  preferably includes a wireline connector  108  to facilitate retrieval of jet pump  88 . 
     Another embodiment of the present invention is illustrated in FIG.  5 . In this embodiment, a jet pump  110  is disposed in a bypass conduit  112 . Bypass conduit  112  is connected to production tubing  22  at an inlet  114  and an outlet  116 . 
     In operation, a submergible pump  118  of pumping system  10 , pumps a production stream upwardly through production tubing  22 . A portion of this production stream is diverted through bypass conduit  112  via inlet  114 . This portion of the fluid flow is routed through jet pump  110  which removes gas accumulated beneath packer  24 . Jet pump  110  pulls gas from wellbore  16  via inlets  120  and combines the gas with the fluid flowing through jet pump  110 , as described generally above. The mixture is then reinjected into the main production stream above packer  24  at outlet  116 . A flow restrictor  122 , such as an orifice, is used to lower the pressure in the main production stream to the pressure of the mixture in order to facilitate the reintroduction of the mixture into the main production stream. 
     In this embodiment, packer  24  preferably is a side pocket packer. Jet pump  110  is mounted directly in the side pocket of packer  24  for ready access to any gas pocket formed beneath packer  24 . 
     It will be understood that the foregoing description is of preferred embodiments of this invention, and that the invention is not limited to the specific form shown. For example, a variety of components can be used or interchanged in a given pumping system; a variety of jet pump designs may be utilized; the pressures within the wellbore, jet pump and production tubing can be controlled according to the specific environment or application; and a variety of packers and deployments systems may be utilized. These and other modifications may be made in the design and arrangement of the elements without departing from the scope of the invention.