Patent Publication Number: US-8113274-B2

Title: Electric submersible pumping system with gas vent

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Divisional U.S. application Ser. No. 12/718,005, filed Mar. 5, 2010, entitled “Electric Submersible Pumping System With Gas Vent” which is a divisional of U.S. application Ser. No. 11/696,315, filed Apr. 4, 2007, now U.S. Pat. No. 7,673,676 incorporated herein. 
    
    
     BACKGROUND 
     Well completions are used in a variety of well related applications involving, for example, the production of fluids. A wellbore is drilled into a geological formation, and a completion is deployed into the wellbore by tubing or other deployment mechanisms. Generally, the wellbore is drilled through one or more formations containing desirable production fluids, such as hydrocarbon based fluids. 
     In many of these applications, electric submersible pumping systems are used to pump fluid from the wellbore to a collection location. However, the formation of free gas at the pump intake of the electric submersible pumping system can severely degrade pumping system performance. In some environments, a gas lock condition can result in which the pump is unable to deliver enough pressure to keep the pumping action continuous. 
     When a packer is used above the electric submersible pumping system, free gas can accumulate below the packer and eventually create a gas pocket that reaches the pump intake and triggers the gas lock condition. Attempts have been made to evacuate the gas accumulated below the packer, but these attempts have met with limited success. Without sufficient removal of the accumulated gas, the submersible pump of the electric submersible pumping system can be exposed to free gas which reduces pumping efficiency and increases the possibility of reaching the gas lock condition. 
     SUMMARY 
     In general, the present invention provides a system and method for pumping fluids from a wellbore. An electric submersible pumping system is deployed into a wellbore on a tubing. Free gas can accumulate around the electric submersible pumping system, but a gas vent is positioned to remove the free gas. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Certain embodiments of 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 elevation view of a completion deployed in a wellbore and having a gas vent positioned to remove accumulated gas, according to an embodiment of the present invention; 
         FIG. 2  is a front elevation view similar to that of  FIG. 1  but showing an example of a gas removal flow path, according to an embodiment of the present invention; 
         FIG. 3  is a front elevation view similar to that of  FIG. 1  but showing an alternate gas removal flow path, according to another embodiment of the present invention; 
         FIG. 4  is a front elevation view of a completion deployed in a wellbore that illustrates another example of a gas vent, according to an alternate embodiment of the present invention; 
         FIG. 5  is a front elevation view of a completion deployed in a wellbore that illustrates another example of a gas vent, according to an alternate embodiment of the present invention; 
         FIG. 6  is a front elevation view similar to that of  FIG. 5  but showing an example of another gas removal flow path, according to an embodiment of the present invention; 
         FIG. 7  is a front elevation view of a completion illustrating an alternate embodiment of the present invention; and 
         FIG. 8  is a front elevation view similar to that of  FIG. 7  but showing an example of another gas removal system, according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, numerous details are set forth to provide an understanding of the present invention. However, it will be understood by those of ordinary skill in the art that the present invention may be practiced without these details and that numerous variations or modifications from the described embodiments may be possible. 
     The present invention generally relates to completions that can be used in subterranean environments to move fluids to a desired location. The completions generally comprise electric submersible pumping systems deployed on tubing, such as production tubing or coiled tubing. The tubing can be utilized as a flow path for fluids produced by the electric submersible pumping system and pumped to a desired collection location. The completions also generally comprise at least one packer positioned to form a seal between the tubing and the surrounding wellbore wall which can be in the form of a wellbore casing. In environments in which the well fluids have a relatively high gas-to-liquid ratio, e.g. 20% or more, the gas can interfere with the pumping efficiency of the electric submersible pumping system. Furthermore, free gas that is separated as well fluid is drawn into a pump intake or that is separated by virtue of a gas separator, collects beneath the packer. One or more gas vents are positioned to remove the accumulated free gas so as not to create a gas lock condition or otherwise interfere with operation of the electric submersible pumping system. 
     Referring generally to  FIG. 1 , one embodiment of a completion  20  deployed in a wellbore  22  is illustrated. The wellbore  22  is drilled into a subsurface formation  24  and may be lined with a casing  26 . The casing  26  typically is perforated to allow flow of well fluids  28  between formation  24  and wellbore  22 . 
     In the embodiment illustrated, completion  20  comprises an electric submersible pumping system  30  deployed on a tubing  32 , such as a production tubing or coiled tubing. The tubing  32  extends through an isolation device  33 , e.g. a packer  34 , which isolates the electric submersible pumping system in wellbore  22 . In the embodiment illustrated, packer  34  forms a seal between tubing  32  and the surrounding wellbore, e.g. casing  26 , to seal off a desired region of wellbore  22 . A power cable  36  also is routed through packer  34  for connection with electric submersible pumping system  30  to provide power for operation of the submersible pumping system. 
     Many types of electric submersible pumping systems  30  may be utilized depending on the environment, wellbore depth, fluid type, and other factors. In the example illustrated in  FIG. 1 , electric submersible pumping system  30  comprises a submersible pump  38  which may be a centrifugal style pump. Submersible pump  38  is powered by a submersible motor  40  supplied with electrical power via power cable  36 . Submersible motor  40  drives submersible pump  38  through a motor protector  42 , and submersible pump  38  draws well fluid into the electric submersible pumping system through a pump intake  44 . Pumping system  30  also may comprise a variety of other components, such as a gas-oil separator  46  and an outlet section  48  by which submersible pumping system  30  is coupled to tubing  32 . 
     Gas collecting beneath packer  34  is removed through a gas vent in the form of a gas inlet  50  typically positioned below packer  34  and above electric submersible pumping system  30 . In the embodiment illustrated, gas inlet  50  extends through the wall of tubing  32  and into a landing profile  52 . The landing profile  52  allows pumped fluids to be conveyed around the landing profile without commingling with free gas entering through gas inlet  50 . 
     Completion  20  also may comprise a variety of other features. For example, one or more sliding sleeves  54  may be positioned along tubing  32 . In the embodiment illustrated, one sliding sleeve  54  is positioned above packer  34  and another sliding sleeve  54  is positioned beneath packer  34 . In some applications, completion  20  also may comprise subsurface safety valves to enable shutting down of the well in case of emergency. For example, a subsurface safety valve  56  may be installed along tubing  32  between electric submersible pumping system  30  and landing profile  52  to stop, if necessary, the flow of fluid pumped by the electric submersible pumping system into tubing  32 . By way of further example, another subsurface safety valve  58  can be installed in gas inlet  50  to stop the flow of free gas into landing profile  52 , if necessary. This combination of subsurface safety valves allows the entire well to be shut off in case of an emergency. 
     Landing profile  52  enables the formation of at least two separate flow paths within tubing  32  so that pumped fluid and free gas can be separately produced to surface locations or other suitable locations, as illustrated in  FIG. 2 . In this embodiment, a second tubing  60  is landed in landing profile  52  and extends upwardly through tubing  32  to a surface location. Second tubing  60  creates a first flow path  62 , located between second tubing  60  and the surrounding tubing  32 , and a second flow path  64  within the interior of second tubing  60 . By way of example, second tubing  60  may be concentrically located within tubing  32 . Furthermore, second tubing  60  may comprise coiled tubing or other suitable tubing. In one embodiment, tubing  32  comprises production tubing, and second tubing  60  comprises coiled tubing deployed along the interior of tubing  32 . 
     In the embodiment illustrated in  FIG. 2 , gas inlet  50  is coupled in fluid communication with second tubing  60  and second flow path  64 . Accordingly, free gas that accumulates beneath packer  34  flows into gas inlet  50 , through the side wall of tubing  32 , through landing profile  52 , and into second tubing  60  for routing to the surface or other collection location along second flow path  64 . Simultaneously, fluid produced by electric submersible pumping system  30  bypasses landing profile  52 , as indicated by arrow  66 . The fluid produced by electric submersible pumping system  30  is produced upwardly along first flow path  62  in the space between the exterior surface of second tubing  60  and the interior surface of tubing  32 . 
     In an alternate embodiment, the free gas is produced along first flow path  62 , and fluid pumped by electric submersible pumping system  30  is produced along second flow path  64 , as illustrated in  FIG. 3 . In this alternate embodiment, landing profile  52  is configured to direct gas entering gas inlet  50  into the space between second tubing  60  and surrounding tubing  32 . Correspondingly, landing profile  52  is configured such that fluid produced by pumping system  30  is produced directly through landing profile  52  and into second tubing  60 , as indicated by arrow  68 . The fluid produced by electric submersible pumping system  30  travels along second flow path  64  separated from the free gas produced along first flow path  62 . 
     Other embodiments of gas vents, e.g. gas inlets, can be utilized to remove free gas accumulated beneath packer  34 . As illustrated in  FIG. 4 , for example, gas inlet  50  is connected directly into a primary flow path  70  along the interior of tubing  32 . A check valve  71  blocks any discharge of pumped fluid into the annulus surrounding tubing  32  while enabling the flow of free gas from below packer  34  and into tubing  32 . The free gas and pumped fluid are commingled for production to a surface location or other collection location. In this embodiment, gas inlet  50  and check valve  71  may be formed as part of a tubing joint  72  positioned in production tubing  32 . A subsurface safety valve  73  may be positioned above packer  34 . This style of completion is amenable to, for example, shallow packer applications. 
     Another alternate embodiment is illustrated in  FIG. 5 . In this embodiment, packer  34  comprises at least three separate pass-through passages  74 ,  76  and  78 . Pass-through passage  74  accommodates the passage of tubing  32  therethrough, and pass-through passage  76  accommodates the passage of power cable  36  therethrough. Pass-through passage  78 , however, is designed to receive a gas vent valve  80  positioned to vent free gas from a position of accumulation beneath packer  34  to an annulus region  82  above packer  34 . Once above packer  34 , the free gas can flow to the surface. An individual gas vent valve  80  or a plurality of gas vent valves  80  can be used to facilitate removal of the pocket of gas that potentially accumulates beneath packer  34 . 
     As illustrated in  FIG. 6 , the one or more gas vent valves  80  can be coupled to one or more gas vent tubes  84 . The gas vent tube  84  provides a specific flow path for containing the produced free gas and directing it to a desired location, e.g. a surface location. In the embodiment illustrated, gas vent tube  84  is positioned along the annulus between tubing  32  and the surrounding casing  26 . 
     Another embodiment of completion system  20  is illustrated in  FIG. 7 . In this embodiment, isolation device  33  comprises a pod assembly  86  that isolates electric submersible pumping system  30  in wellbore  22 . A tubing  88  extends downwardly from the pod assembly  86  through a packer  90  to a region of wellbore  22  beneath packer  90 . The electric submersible pumping system  30  draws fluid from this region of the wellbore and into pod assembly  86  through tubing  88 . 
     Free gas can collect within pod assembly  86  and rise to an upper region  92  of pod assembly  86 , capped by a top  94 . As illustrated in  FIG. 7 , a tubing  96  can be placed in fluid communication with the upper region  92  to enable the outflow of accumulated free gas. For example, tubing  96  can be directed through top  94 . Free gas flows upwardly through tubing  96  and into gas inlet  50 . Depending on the configuration of landing profile  52 , the free gas can be directed along either first flow path  62  or second flow path  64 . In this example, a subsurface safety valve  98  is deployed in tubing  32  between landing profile  52  and pod assembly  86 . Another subsurface safety valve  100  may be positioned in tubing  96 . 
     An alternate embodiment utilizing pod assembly  86  is illustrated in  FIG. 8 . In this embodiment, landing profile  52  and gas inlet  50  are positioned within pod assembly  86  below top  94  in upper region  92 . Again, the free gas can be directed along first flow path  62  or second flow path  64  depending on the design of landing profile  52 . The fluid pumped by electric submersible pumping system  30  is directed along the other of the first and second flow paths. In the embodiment illustrated in  FIG. 8 , for example, fluid pumped by electric submersible pumping system  30  is directed along first flow path  62 , as indicated by arrow  102 . 
     The embodiments described above provide examples of completion systems that utilize an electric submersible pumping system in combination with a gas vent to remove free gas from a specific collection area. The gas vents are particularly useful in venting gas from beneath a packer used to segregate a section of the wellbore. The gas vent embodiments comprise a variety of gas inlets and other types of vents that can remove this accumulated gas before it becomes detrimental to operation of the electric submersible pumping system. It should be noted that many additional or alternate components can be used in constructing the electric submersible pumping system and other aspects of the completion. Additionally, the style of the gas vent, the number of gas vents utilized, and the location of the gas vents can vary from one application to another. 
     Accordingly, although only a few embodiments of the present invention have been described in detail above, those of ordinary skill in the art will readily appreciate that many modifications are possible without materially departing from the teachings of this invention. Such modifications are intended to be included within the scope of this invention as defined in the claims.