Abstract:
A method and apparatus for reducing erosion and friction losses in a wellbore using a power cabled deployed electric submersible pump (ESP). The apparatus can include an ESP disposed within production tubing, wherein a portion of the production tubing surrounding the ESP contains fluid openings that are operable to allow produced fluids to flow outward, thereby increasing the available volume for the produced fluids. The increased volume results in lower fluid velocities of the produced fluid, which advantageously reduces erosion and friction loss.

Description:
TECHNICAL FIELD OF THE INVENTION 
     Embodiments of the present invention relates to a method and apparatus for avoiding erosion and high friction loss for power cable deployed electric submersible pump (ESP) systems. 
     BACKGROUND OF THE INVENTION 
     For certain production wells, artificial lift systems can become necessary when the natural pressure within the underground reservoir is no longer adequate to naturally push produced fluids to the surface. Electric submersible pumps (ESPs) are often used in these situations. Electric power is transmitted from the surface via an umbilical power cable to the downhole ESP. Conventionally, ESPs were deployed at the end of production tubing, with the power cable installed outside the production tubing. However, electrical failures were often associated with this type of setup, and anytime there was an electrical failure, a rig had to be brought in to pull out the production tubing and the ESP. 
     In an effort to overcome this problem, alternative ESP systems were developed. One such system is a power cable deployed ESP system. In this system, the power cable is used to transmit power, as well as to support the ESP itself. In this alternate setup, both the power cable and the ESP are installed inside the production tubing. 
     In order to improve overall safety for a power cable deployed ESP system, well control can employ a deep set surface controlled subsurface safety valve (SCSSV). The SCSSV is installed in the production tubing below the ESP. The SCSSV is designed to be fail-safe, so that the wellbore is isolated in the event of any system failure or damage to the surface production-control facilities. An example of a prior art setup is shown in  FIG. 1 . 
     In  FIG. 1 , production tubing  40  is disposed within casing  20 . ESP  90  is supported by power cable  100 , as well as production tubing  40  via isolation member  120 . Casing  20  has perforations  22  in a producing region  30  of an underground reservoir. Produced fluids enter casing  20  through perforations  22 . The produced fluids then travel through the safety valve  80  into an inner volume  105  of production tubing  40 , and flow through a narrow gap between ESP  90  and production tubing  40 . The produced fluid then enters ESP  90  via intake slots  97 , travels through medial pump body portion  98 , and exits ESP  90  above isolation member  120  via discharge slots  111 . The produced fluid is now back within production tubing  40  (at a point above isolation member  120 ), where it can be pumped to the surface. Lower packer  50  prevents produced fluids from traveling up the annular region formed between production tubing  40  and casing  20 . 
     In these types of setups, the fluid velocity of the production fluids can get quite high due to the narrow gap between the production tubing and the ESP. In typical installations, the narrow gap can range from 0.079 inch to 0.225 inch, depending on the size of the production tubing and chosen ESP. For a typical target rate of 6,000 barrels per day (bpd) production using production tubing of 4½ inch, the fluid velocity of the produced fluid coming through this gap can be 70 ft/s. For 5½ inch tubing, the velocity can still reach 40 ft/s. However, at fluid velocities in this range, the ESP system can fail quickly due to erosion. Additionally, at high velocities such as these, the frictional losses are quite significant. Overcoming frictional losses is usually achieved using longer motors and longer pumps; however, doing this increases the capital costs. Additionally, longer equipment increases installation difficulties, particularly for live well deployment with a surface lubricator. As such, ESP systems are typically only operated at 1,000 to 2,000 bpd. 
     Therefore, it would be advantageous to provide an ESP system that did not suffer from erosion or high friction losses at production rates higher than 2,000 bpd. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a method and apparatus that provides one or more of these benefits. In one embodiment, the invention provides for an ESP assembly for use in a wellbore, wherein the ESP assembly includes a pump and a tubing section adapted for insertion within casing of the wellbore thereby defining an annulus between the tubing section and the casing. The tubing section circumferentially surrounds a portion of the pump. The tubing section includes fluid openings that are operable to allow fluid from the wellbore to flow radially outward, thereby occupying a greater volume, and therein reducing the bulk fluid velocity of the fluid. The pump can include a fluid inlet, a seal section, a pump discharge and a pump motor coupled to the pump. 
     In one embodiment, the tubing section can be integral within a string of production tubing that is adapted for insertion into the wellbore. In another embodiment, the ESP assembly further includes a safety valve positioned at a lower end of the tubing section. The safety valve has an open and closed position, and the safety valve is positioned such that fluid from the wellbore enters the tubing section through the safety valve when the safety valve is in an open position. In another embodiment, the ESP assembly can further include a safety valve control line that is in communication with the safety valve. 
     In one embodiment, the fluid openings are selected from the group consisting of slots, holes, perforations, and combinations thereof. Those of ordinary skill in the art will recognize that the fluid openings can be of any size, shape, and pattern so long as the integrity of the production tubing is maintained. In one embodiment, the fluid openings are perforations having diameters in the range of ¼ inch to ½ inch. In another embodiment, the ESP assembly can include a lower packer and an upper packer, wherein the lower packer is connected to the casing and the production tubing, the lower packer being positioned proximate the lower end of the production tubing, the lower packer being operable to support the positioning of the production tubing within the casing. The upper packer is connected to the casing and the production tubing, and the upper packer is positioned at a point above the lower packer thereby forming a first interstitial space in the annulus between the upper packer and the lower packer. A second interstitial space is also formed in the annulus between the upper packer and the surface. 
     In another embodiment, the ESP assembly for use in a wellbore can include casing, production tubing, the lower packer, the upper packer, the safety valve, and the safety valve control line in communication with the safety valve. The casing is positioned within a hydrocarbon wellbore and is in fluid communication with a producing region of a reservoir such that produced fluid can enter the casing. The production tubing is positioned within the casing to provide a pathway for produced fluids dispersed from the hydrocarbon well. The production tubing has a diameter that is less than the diameter of the casing such that an annulus is formed between an outer wall of the production tubing and an inner wall of the casing, wherein the production tubing has a lower end that is distal from the surface. The lower packer is connected to the casing and the production tubing and is positioned proximate the lower end of the production tubing. The lower packer is operable to support the positioning of the production tubing within the casing. The upper packer is connected to the casing and the production tubing. The upper packer is positioned at a point above the lower packer, thereby forming the first interstitial space in the annulus between the upper packer and the lower packer. The second interstitial space is formed in the annulus between the upper packer and the surface. The safety valve is positioned on an inner wall of the production tubing proximate the lower packer, and the safety valve has an open position and a closed position. The first interstitial space is in fluid communication with the production tubing, such that the assembly is operable to allow produced fluid from the producing region of the reservoir to flow from the production tubing into the first interstitial space. This causes the fluid velocity of the produced fluid to be less than the fluid velocity of the produced fluid if the first interstitial space was not in fluid communication with the production tubing. 
     In another embodiment, the ESP assembly can also include an absence of perforations in the casing in areas other than proximate the producing region of the reservoir. In another embodiment, the casing does not allow produced fluids to reenter the reservoir. In another embodiment, the second interstitial space is not in fluid communication with the production tubing. 
     In another embodiment, the assembly is operable to house an ESP within the production tubing. The ESP can include a pump intake, a pump discharge, a medial pump body portion, an isolation member, a motor, and a seal section. The pump intake can be positioned above the safety valve so that the produced fluids enter the pump intake. The pump discharge can be positioned above the upper packer and within the production tubing so that the produced fluids are discharged within inner walls of the production tubing and sent to the surface. The medial pump body portion can extend between the pump intake and the pump discharge and can also provide a pathway through which the produced fluids flow from the pump intake to the pump discharge. The isolation member can be positioned at an upper portion of the ESP, and the isolation member is operable to isolate the pump intake from the pump discharge. The motor is connected to the ESP and provides power to the ESP. The seal section can be connected between the motor and a distal end portion of the pump intake, with the seal section being operable to prevent produced fluids from entering the motor. In another embodiment, the second interstitial space is not in fluid communication with the ESP. 
     In another embodiment, the portion of the tubing between the upper packer and safety valve can include fluid openings for allowing the produced fluids to enter the first interstitial space. In another embodiment, the perforations fluid openings can have diameters in the range from ¼ inch to ½ inch. In another embodiment, the casing can extend through the producing region of the reservoir. In one embodiment, the fluid velocity of the produced fluid can be maintained below 20 fps when producing more than 2,000 bpd. In another embodiment, the fluid velocity of the produced fluid is maintained between 10 to 20 fps when producing up to 6,000 bpd. In another embodiment, the fluid velocity of the produced fluid is maintained below 20 fps when producing up to 32,000 bpd for 4½ inch tubing (7 inch casing). In another embodiment, the fluid velocity of the produced fluid is maintained below 20 fps when producing up to 45,000 bpd for 7 inch tubing (9⅝ inch casing). 
     Embodiments of the present invention also include a method for enhanced well control of high fluid velocity wells. In one embodiment, the method can include providing any ESP assembly discussed herein, inserting the ESP assembly into a wellbore that is in fluid communication with an underground hydrocarbon reservoir, and flowing fluid from the underground hydrocarbon reservoir through the fluid openings of the tubing string and radially outward, such that the fluid occupies a greater volume of space, thereby lowering the fluid velocity of the fluid. 
     In another embodiment, the invention can include a method for enhanced well control for high fluid velocity wells can include the steps of positioning casing into a bore of a hydrocarbon well, positioning production tubing at least partially within the casing, connecting a lower packer to the casing and the production tubing, connecting an upper packer to the casing and the production tubing, positioning a safety valve on an inner wall of the production tubing proximate the lower packer, communicating with the safety valve, and allowing produced fluids to flow from the reservoir through the opening of the safety valve to the production tubing and the first interstitial space, such that the fluid velocity of the produced fluid is less than the fluid velocity of the produced fluid if the first interstitial space was not in fluid communication with the production tubing. 
     In another embodiment, the method can also include the step of operating the ESP so that the produced fluids enter the ESP, flow through the ESP, and discharge from the ESP back into the production tubing above the isolation member and then travel on to the surface. In another embodiment, the second interstitial space is not in fluid communication with the ESP. In another embodiment, the hydrocarbon well is located offshore. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, claims, and accompanying drawings. It is to be noted, however, that the drawings illustrate only several embodiments of the invention and are therefore not to be considered limiting of the invention&#39;s scope as it can admit to other equally effective embodiments. 
         FIG. 1  is a front elevational view of an apparatus in accordance with an apparatus known in the prior art. 
         FIG. 2  is a front elevational view of an apparatus in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     While the invention will be described in connection with several embodiments, it will be understood that it is not intended to limit the invention to those embodiments. On the contrary, it is intended to cover all the alternatives, modifications and equivalents as may be included within the spirit and scope of the invention defined by the appended claims. Like numbers refer to like elements throughout. 
     Embodiments of the present invention can improve ESP performance in most any reservoir; however, the embodiments are most advantageous in wells that typically experience higher than normal friction losses or erosion damage to an ESP. Pressure losses at or above 50 psi are generally regarded as high friction losses. As will be understood by those skilled in the art, embodiments of the present invention, for example, also can allow produced fluids to more readily flow when pumped by use of an ESP. While the embodiments shown in the figures generally show vertical bores, those of ordinary skill in the art will understand that embodiments of the present invention can also apply to horizontal bores. Therefore, embodiments of the present invention are useful for pumping produced fluids from either a horizontal bore or vertical bore of a hydrocarbon well to the surface. 
     High fluid velocity can result in premature failure of down hole components such as an ESP due to erosion damage. Accordingly, embodiments of the present invention can enhance well control, for example, by improving production rates and reducing the rate of premature failure of an ESP. 
     Now turning to  FIG. 2 . Embodiments of the present invention include positioning casing  20  within wellbore  10 . The bottom of the well can be an open-hole, cased-hole completion, or any other bottom hole completion, as will be understood by those skilled in the art, to be suitable for embodiments of the present invention. For example, an open-hole, top set, or barefoot completion can be made by drilling down producing region  30  and subsequently casing wellbore  10 . According to this embodiment, wellbore  10  is drilled through producing region  30  leaving the bottom of wellbore  10  open. Casing  20  in a cased-hole completion, according to another embodiment of the present invention, is run through the producing region  30 , and cemented in place. As illustrated in  FIG. 2 , according to this embodiment, perforations  22  are made in casing  20  to allow produced fluids to fluidly travel from producing region  30  of the underground reservoir to within casing  20  and eventually onward to the surface. 
     After casing  20  is positioned within wellbore  10 , cement is pushed between the outer walls of casing  20  and the inner walls of wellbore  10  to set casing  20  thereto. Casing  20 , for example, can prevent the contamination of fresh water zones. Casing  20  can be made out of steel pipe to support wellbore  10 , and in accordance the American Petroleum Institute specifications and standards as understood by those skilled in the art. 
     To further support wellbore  10 , and to provide a pathway for produced fluids dispersed from wellbore  10  to the surface, embodiments of the present invention include production tubing  40 . Production tubing  40  has an outside diameter that is less than the inside diameter of casing  20 . Lower packer  50  is positioned between outer walls of production tubing  40  and inner walls of casing  20  and is also positioned proximate the lower end of production tubing  40 . Lower packer  50  is adapted to support the positioning of production tubing  40  within casing  20 , as well as also to prevent produced fluids from entering first interstitial space  70  without first passing through safety valve  80  when safety valve  80  is in an open biased position. When safety valve  80  is in a closed biased position, lower packer  50 , in conjunction with safety valve  80 , prevents produced fluids from entering first interstitial space  70 . 
     As illustrated in  FIG. 2 , embodiments of the present invention include ESP  90  being operable to pump produced fluids from wellbore  10  and thereby fluidly travel to the surface. In the embodiment shown in  FIG. 2 , ESP  90  is positioned entirely within production tubing  40 , with a portion of ESP  90  extending below isolation member  120  and a portion extending above isolation member  120 . The portion of ESP  90  disposed below isolation member  120 , e.g., further down hole. can include, for example, motor  92 , seal sections  94 , pump intake  96 , and at least a region of medial pump body portion  98 . The outer diameter of ESP  90  has a smaller diameter than the inner diameter of production tubing  40 . 
     During operation, according to certain embodiments of the present invention, motor  92  receives power through power cable  100 . In one embodiment, ESP  90  can include one or more centrifugal pumps (not shown) within medial pump body portion  98 . The one or more centrifugal pumps suction produced fluids from inner volume  105  within production tubing  40 . The produced fluids are suctioned from inner volume  105  through a plurality of intake slots  97 , and pumped by the one or more centrifugal pumps to increase the pressure and flow of the produced fluids that entered pump intake  96 . The produced fluids are then sent to pump discharge  110  and discharged through a plurality of discharge slots  111  to a proximal region within the inner walls of the production tubing  40  and onward to the surface. The outer areas of pump discharge  110  and pump intake  96  are separated by isolation member  120 . During operation, isolation member  120  provides a barrier to allow for a pressure differential to form across isolation member  120  due to the produced fluids being pumped from pump intake  96  to pump discharge  110 . 
     In one embodiment, ESP  90  includes motor  92  to drive one or more centrifugal pumps within medial pump body portion  98 . Motor  92 , for example, can be the most down hole major component of ESP  90 . During operation, motor  92  runs in the range of speed of about 2,500 to 3,500 rev/min. In some embodiments, motors that are operable to run at about 10,000 RPM could be used. Those of ordinary skill in the art will recognize that the speed is related to the exact equipment used. As will be understood by those skilled in the art, during operation, the flow of produced fluids that pass the outer surfaces of the motor also can act as a coolant to reduce heat associated with operation of ESP  90  to thereby assist in preventing ESP  90  from overheating. 
     Embodiments of ESP  90  further include one or more seal sections  94  to prevent produced fluids from entering within inside surfaces of motor  92 . In addition to preventing produced fluids from entering the inside surfaces of motor  92 , the one or more seal sections  94  equalizes external bottom hole pressures and internal pressures of the motor  92 . Moreover, as will be understood by those skilled in the art, the one or more seal sections  94  allows lubricant associated with motor  92  to thermally expand and contract. 
     ESP  90  can also include pump intake  96  whereby produced fluids enter ESP  90 . Pump intake  96  includes a plurality of intake slots  97  that are preferably evenly spaced in a location where the produced fluids are suctioned therethrough. The plurality of intake slots  97  can be a variety of uniform shapes including, but not limited to, spherical, ellipsoidal, or rectangular as understood by those skilled in the art. Pump intake  96  preferably is connected between a proximal end portion of the one or more seal sections  94  and a distal end portion of medial pump body portion  98  as illustrated in  FIG. 2 . 
     Medial pump body portion  98  can include one or more centrifugal pumps to pump the produced fluids that enter ESP  90 . The horsepower of the one or more centrifugal pumps ranges from about 75 to 300 during operation. The one or more centrifugal pumps increase the flow rate of the produced fluids entering ESP  90  to artificially lift the produced fluids to the surface. In a preferred embodiment of ESP  90 , the one or more centrifugal pumps have a large number of stages, each stage having an impeller and a diffuser. Medial pump body portion  98  extends between pump intake  96  and pump discharge  110  so that produced fluids flow therebetween from pump intake  96  to pump discharge  110 . 
     Embodiments of the present invention can also include isolation member  120  disposed between pump discharge  110  and medial pump body portion  98 . According to embodiments of the present invention, isolation member  120  connects to the inner walls of production tubing  40  to support the positioning of ESP  90 . 
     ESP  90  can include pump discharge  110  to discharge the produced fluids for onward transfer within production tubing  40  to the surface. Pump discharge  110 , for example in one embodiment, includes a plurality of discharge slots  111  that can be evenly spaced in a location where the produced fluids are discharged to a proximal region within the inner walls of production tubing  40 . The plurality of discharge slots  111 , as will be understood by those skilled in the art, can be a variety of uniform shapes including, but not limited to, spherical, ellipsoidal, or rectangular. As illustrated by the arrows in  FIG. 2 , for example, pump discharge  110  is positioned within production tubing  40  so that produced fluids discharge through discharge slots  111  and fluidly travel through production tubing  40  and onward to the surface. 
     Embodiments of the present invention can include, for example, safety valve  80  being operable to prevent produced fluids from flowing into inner volume  105  of production tubing  40  when safety valve  80  is in the closed position. Safety valve  80  selectively, or in the case of an emergency, assists to prevent produced fluids from dispersing to the surface. Safety valve  80 , according to an embodiment of the present invention, is connected to the inner walls of production tubing  40  and is distally disposed from ESP  90  within production tubing  40 . In one embodiment, safety valve  80  can be a deep set surface controlled subsurface safety valve (SCSSV). Industry well control policy requires all wells that are in close proximity to people or facilities to be equipped with an SCSSV. Conventionally, the SCSSV is shallow set (e.g. about 200-300 It below the wellhead). However, in embodiments of the present invention, safety valve  80  is deep set (e.g. located below ESP  90 ). 
     Embodiments of the present invention also include upper packer  60  and first interstitial space  70 . First interstitial space  70  being the annular volume created between casing  20  and production tubing  40 , and lower packer  50  and upper packer  60 . In one embodiment, a portion of production tubing  40  below isolation member  120  and above safety valve  80  contains fluid openings  140 , such that first interstitial space  70  is in fluid communication with inner volume  105  of production tubing  40 . The produced fluid can now travel all the way to casing  20 , affectively increasing the available volume, which in turn reduces the fluid velocity of the produced fluids. 
     Upper packer  60  is adapted to prevent produced fluids from flowing in the annular area between the inner walls of casing  20  and the outer walls of production tubing  40  above upper packer  60 , hereby defined as second interstitial space  130 . 
     During operation, produced fluids are produced from producing region  30  and flow through perforations  22  to the inner walls of casing  20  distal from safety valve  80 . According to an embodiment of the present invention, power and communication are transmitted to safety valve  80  through safety valve control line  82  connected to a proximal end of safety valve  80 . In one embodiment, safety valve control line  82  receives power from the surface. In another embodiment (not shown), safety valve control line  82  can receive power directly from the ESP. When safety valve  80  is in the “open” position, produced fluids flow safety valve  80  to inner volume  105  of production tubing  40  before entering first interstitial space  70 . When safety valve  80  is in the “closed” position, produced fluids are prevented from traveling to inner volume  105  of production tubing  40  or first interstitial space  70 . Safety valve  80 , as will be understood by those skilled in the art, preferably is in a fall-back mode so that any interruption or malfunction should result in safety valve  80  being in the closed position. 
     In another embodiment, safety valve control line  82  can be removed and replaced with a wireless communication device that is operable to communicate with safety valve  80  wirelessly. Moreover, as will be understood by those skilled in the art, embodiments of the present invention can include communicating by hydraulic or pneumatic methods as well. 
     While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed.