Abstract:
A device and method for inhibiting particle (e.g., sand) accumulation on down hole equipment, such as an ESP, particularly when the equipment is not in use. The device and methods permit the equipment to start and stop with fewer break downs and at greater efficiency. The device includes a central tubular section connecting the equipment to the production tubing string. The tubular section is surrounded by an annulus and a number of ports in the tubular section angled to allow fluid communication between the tubular section and the annulus during operation, but prevent particles from flowing from the annulus into the tubular section when not in use. A check valve between the tube and ESP assists in isolating the ESP from sand.

Description:
PRIORITY CLAIM 
       [0001]    The present application claims priority to U.S. Provisional Application No. 62/334,174 filed May 10, 2016, which is incorporated by reference herein. 
     
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
       [0002]    This invention relates to systems and methods to prevent particle interference with downhole equipment, such as an electrical submersible pump (ESP). 
       2. Description of the Relevant Art 
       [0003]    Management of sand in the well bore has long been an issue. Many oil and gas wells are in sand-producing intervals, such as sandstones. There are several forms of artificial lift of the production fluids, with the most common being the electrical submersible pump (ESP). In recent years, unconventional wells have gained wide spread acceptance and often involve horizontal production tubing, ESP&#39;s for lift, and multiple, highly fractured production intervals, often in shale or other unconsolidated formations. 
         [0004]    In such highly fractured, horizontal wells, the use of proppants, such as sand, to maintain the frac efficiency has increased. That is, there is a trend to use even more proppant per lateral foot of wellbore. Many ESP pumps have been manufactured to operate on sand filled fluid without significant numbers of failure. However, ESP&#39;s are often stopped, both intentionally and unintentionally. For example, electric reliability and power fluctuations often stop ESP operation or the ESP is stopped for maintenance or production issues. “Sand, particles and proppants” are sometimes used interchangeably for simplicity herein. 
         [0005]    When an ESP stops operating, the sand in the production fluid tends to settle in the production tubing. The sand settles on the ESP which not only induces component failures in the ESP, but also makes restart of the ESP difficult because the ESP must first clear substantial amounts of sand from the production tubing. Failure and replacement of an ESP is not only expensive because of the rework required in the well, but also because of the lost production time.
       Several attempts have been made to prevent sand accumulation on ESP&#39;s particularly when the ESP is idle. See e.g., CN Pat. Pub. No. 1,955,438, PCT App. Pub. No. WO2007083192, U.S. Pat. No. 6,289,990, U.S. Pat. No. 7,048,057, U.S. Pat. No. 9,181,785 and U.S. Pat. No. 9,441,435 (incorporated by reference). However, each of these existing tool designs has limitations which lead to suboptimal performance, and many are unnecessarily complex and expensive. Thus, a need continues to exist for a tool design that will automatically and cost effectively prevent the accumulation of sand on an ESP, without redepositing the sand below the ESP, potentially preventing the restarting of the ESP or requiring other steps to purge the production tubing of accumulated sand.       
 
       SUMMARY OF THE INVENTION 
       [0007]    Problems with ESP operation are addressed by the device and methods of the present invention which tend to prevent particle accumulation on the ESP when not in use and provide for more efficient operation. Therefore the reliability, efficiency, timeliness and the likelihood of a successful restart of an ESP is greatly increased. Generally, the device prevents particle interference with lifting equipment, such as an ESP, in a well bore having a production tubing string using a tube positioned between the lifting equipment and the surface and in fluid communication with the lifting equipment and the production tubing string. An annulus portion is defined around the tube, e.g. with a cylinder spaced from and surrounding the tube. The device includes a check valve proximate at least one end of the tube which operates to permit fluid flow from the lifting equipment to the surface, but prevents fluid flow from the tube to the lifting equipment. The device has a plurality of ports positioned in the wall of the tube which operate to permit fluid flow from the tube into the annulus during operation of the lifting equipment and operable to inhibit particles from entering the tube when the lifting equipment is not operating. Preferably, the ports are angled in the direction of the lifting equipment and can be more dense closest to the lifting equipment. 
         [0008]    One method of the present invention operates to inhibit particle impediment to lifting equipment, such as an ESP, when not in use. Generally, the lifting equipment is positioned in the well bore downhole from the surface and operable to pump fluid through a production tubing string to the surface. A particle-excluding device is connected to the production tubing string between the lifting equipment and the surface, the device having a central tubular portion, a surrounding annulus portion, a plurality of spaced ports communicating between the tube and the annulus and a check valve between the ports and the lifting equipment. The lifting equipment is operated so that fluid flows through the check valve, ports, tubular portion and at least some of the annulus portion and into the production tubing. The method inhibits particles in the fluid from accumulating on the lifting equipment when the lifting equipment is not in use by trapping a substantial portion of particles in the annulus, whereby the ports inhibit particle flow into the tubing portion. The check valve prevents reverse fluid flow to the lifting equipment when not in use, and thus prevents the ESP from spinning backwards due to a reversal of the fluid flow. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the accompanying drawings. 
           [0010]      FIG. 1  is a schematic, sectional view of a first embodiment of a device in accordance with the present invention with the production fluid flowing normally; 
           [0011]      FIG. 2  is a sectional view of the device of  FIG. 1  with the flow of the production fluid stopped; 
           [0012]      FIG. 3  is a sectional view of the device of  FIG. 1  with the production fluid starting flow after having stopped; 
           [0013]      FIG. 4  is a sectional view of a detail of a port in the device of  FIGS. 1-3  and  FIGS. 6-9  showing normal production fluid flow; 
           [0014]      FIG. 5  is a sectional view of a detail of a port in the device of  FIGS. 1-3  and  FIGS. 6-9  showing production fluid flow stopped; 
           [0015]      FIG. 6  is a schematic, sectional view of a second embodiment of a device in accordance with the present invention with the production fluid flowing normally from an ESP to the surface; 
           [0016]      FIG. 7  is a sectional view of the device in  FIG. 6  with the flow of the production fluid stopped; 
           [0017]      FIG. 8  is a sectional view of the device in  FIG. 6  with the production fluid starting flow after having stopped; 
           [0018]      FIG. 9  is a cross section view of the device in  FIG. 6  taken as shown; and 
           [0019]      FIG. 10  is a side elevational view of an exemplary operational embodiment of a device in accordance with the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0020]    Turning to the drawings, a first embodiment of a device  10  in accordance with the present invention is illustrated in  FIGS. 1-5 . The device  10  is inserted as part of the production tubing string with  FIG. 1  showing production tubing  12  leading to the surface and ESP  14  located downhole adjacent to the device  10 . It should be understood that the device  10  can be spaced from the ESP and in fact, multiple devices  10  can be used in the production tubing string. Further, while  FIG. 1  appears as a conventional vertical orientation, the device  10  can also be used in horizontal wells. Additionally, while the usefulness of the device  10  is illustrated in this embodiment as protecting an ESP, other downhole devices can be similarly protected from particles such as sand or fracking proppants. 
         [0021]    Generally, the device  10  includes a central production tube  16  surrounded by an enlarged cylinder housing  18 . Thus, the area between the tube  16  and the inner walls of the cylinder  18  define an annulus  20 . At each end of the tube  16  is a check valve  21 ,  22 .  FIGS. 1-3  illustrate a ball check valve, but other types of check valves known in the art can be used, such as diaphragm check valve, swing check valve or tilting disc check valve, stop-check valve, lift-check valve, in-line check valve, duckbill valve, or pneumatic non-return valve. The check valve  21 ,  22  illustrated has a pre-tensioned spring to bias a ball into a seat in a closed position and designed to open at a particular pressure. The check valves  21 ,  22  of  FIG. 1  are open. A number of ports  24  are arranged along the length of the tube  16  providing fluid communication between the production tube  16  and the annulus  20 . 
         [0022]    An end packer  26  is illustrated in  FIG. 1  as defining the terminus for the cylinder  18 . It should be understood, however, that any seals are acceptable, such as an O-ring bore seal. While the device  10  is illustrated as a discrete device inserted as part of the production tubing string, it can be appreciated that the cylinder  18  and annulus  20  could be defined by setting a packer at each end of a casing section to encompass the tube  16  and valves  21 ,  22 . 
         [0023]    During normal operation ( FIG. 1 ) most of the production fluid flows from the ESP through tube  16 , but at least part of the fluid within the tube  16  exits the tube  16  through the ports  24  into the annulus. The fluid streams from within the tube  16  and annulus  20  recombine in the region of the top of the tube  16  proximate check valve  21  to flow up the production tubing. 
         [0024]    In  FIGS. 2-5  the same components as  FIG. 1  are generally illustrated at various stages of the well operation. In  FIG. 2 , the ESP is off and production fluid flow has ceased. Therefore, particles such as sand  30  settles downward in the annulus  20 . The check valves  21  (if utilized),  22  are closed and movement of the sand entrained in the fluid is illustrated by the down arrows. Check valve  21  prevents particle flow into the tube  16 . Particles  30  tends to build up in the annulus  20  near the lower check valve  22 , but does not appreciably flow into the tube  16  through the ports  24 ; the design and orientation of the ports  24  prevent sand to flow into the tube  16 . 
         [0025]    In  FIG. 3 , the ESP  14  is turned on and there are no are no significant buildup of particles  30  on top of the ESP discharge, i.e. in the tube  16 . Both check valves  21 ,  22  immediately open and production fluid flow through the tube  16  up the production tubing to the surface begins almost immediately. As shown in  FIG. 3 , a number of the uppermost ports  24  are not covered by particles  30  and some of the fluid in the tube  16  flows through the ports  24  into the annulus  20 . The particles  30  cover some of the lower ports  24  (e.g., ports  24  near the lower check valve  22 ) and little fluid flow occurs through these lower ports  24 . However, the density of the particles  30  in the fluid in the annulus decreases towards the surface, allowing some fluid flow through the ports  24  into the annulus. This allows the annulus to be self-clearing over time. That is, as the upper ports  24  become partially uncovered with sand, fluid flows from the tube  16  through the ports  24  into the annulus helping to clear the remaining sand. 
         [0026]      FIGS. 4 and 5  are cross sections of a port  24  through the wall of the tube  16 . In  FIG. 4 , the ESP  14  is operating (e.g., as in  FIG. 1 ) and fluid is flowing from the tube  16  through the port  24  into the annulus  20 . The arrow in  FIG. 4  illustrates the fluid flow direction. Each port  24  is downwardly angled (relative to the fluid flow directions in  FIG. 1 ) so that fluid will flow from the tube to the annulus  20 , but particles  30  will not easily flow from the annulus  20  into the tube  16 .  FIG. 5  illustrates this tendency of particles  30  to not flow from the annulus  20  into the tube  16  when the ESP is not operating, such as  FIG. 2 . 
         [0027]    The “downward” angle of the port  24  is greater than perpendicular, but the optimum angle is dependent on the orientation of the device  10  (vertical vs. horizontal), the density of the sand  30  and the composition of the fluid. It is believed that about a 45′ angle will work for most vertical applications, and preferably between 30-60′. The use of the angled ports  24  is believed advantageous over resistive mesh screens to prevent sand from entering the tube and hindering operation of the ESP  14 . The design of ports  24  includes consideration not only of the angle, but also the diameter of the port  24 . The design of the ports  24  also takes into consideration the wall thickness (weight) of the tube  16 . In  FIG. 5  a vertical (or near vertical) well is illustrated and the design of port  24  includes an angle in the direction opposite fluid flow and diameter of the port ( 24 ) such that particles cannot flow into the tube ( 16 ) as shown. The size of the ports can be much larger than mesh screens thus allowing more flow area to be achieved. The size of the ports may also be non-uniform and vary in size depending on desired flow characteristics. While the port cross-section is circular, other geometries are acceptable such as elongated slots or square cross-sections. The ports may be variable in size, variable spacing and variable densities. 
         [0028]    While the device  10  is illustrated in the context of a vertical well bore in the figures, it will be understood that horizontal wells can benefit from the use of the device  10 . In fact, horizontal wells make extensive use of proppants for fracking which is a prime contributor to particles in the production tubing which can settle onto an ESP and hinder operation. Additionally, while protection of ESP&#39;s is a prime use of the device  10 , other downhole equipment can be protected from particle interference as well. 
         [0029]    A second embodiment of a device  50  in accordance with the present invention is illustrated in  FIGS. 6-9 . The device  50  is inserted as part of the production tubing string with  FIG. 6  showing production tubing  12  leading to the surface and ESP  14  located downhole adjacent to the device  50 . It should be understood that the device  50  can be spaced from the ESP and in fact, multiple devices  50  can be used in the production tubing string. Further, while  FIG. 6  appears as a conventional vertical orientation, the device  50  can also be used in horizontal wells. Additionally, while the usefulness of the device  50  is illustrated in this embodiment as protecting ESP  14 , other downhole devices can be similarly protected from particles such as sand or fracking proppants. 
         [0030]    Generally, the device  50  includes a central cylindrical tube  56  surrounded by an enlarged cylinder housing  58 . Thus, the area between the tube  56  and the inner walls of the cylinder  18  define an annulus  60 . At the distal end  72  of the tube  56 , nearest the ESP  14 , is a check valve  62 . At the proximal end  74  of the tube  56 , nearest the surface, is a cap  66 . As with the first embodiment check valves known in the art can be used, such as ball type check valves, diaphragm check valve, swing check valve or tilting disc check valve, stop-check valve, lift-check valve, in-line check valve, duckbill valve, or pneumatic non-return valve. The cap  66  is fixed to prevent fluid flow to or from the tube  56  in the region of the cap  66 . The check valve  62  of  FIG. 6  is open. A number of ports  24  are arranged along the distal end  72  of the tube  56  providing fluid communication between the tube  56  and the annulus  60 . A few ports  24  are provided near the proximal end  74  as seen in  FIGS. 6-9 . That is, the density of the ports  24  is greatest near the distal end  72 . 
         [0031]    An end packer  68  is illustrated in  FIG. 6  as defining the terminus for the cylinder  18  near the distal end  72 . It should be understood, however, that any seals are acceptable, such as an O-ring bore seal. One or more centralizers  70  are shown for maintaining the tube  56  central in the cylindrical housing  58 . While the device  50  is illustrated as a discrete device inserted as part of the production tubing string, it can be appreciated that the cylinder  58  and annulus  60  could be defined by setting a packer at each end of a casing section to encompass the tube  56 , cap  66  and valve  62 . 
         [0032]    During normal operation ( FIG. 6 ) the production fluid flows from the ESP through tube  56 , but all of the fluid within the tube  56  exits the tube  56  through the ports  24  into the annulus  60 . The fluid stream from within the annulus  60  flows up the production tubing  12 . 
         [0033]    In  FIGS. 7-9  the same components as  FIG. 6  are generally illustrated at various stages of the well operation. In  FIG. 7 , the ESP is off and production fluid flow has ceased. Therefore, particles such as sand  30  settle downward in the annulus  60 . The check valve  62  is closed and movement of the sand entrained in the fluid is illustrated by the down arrows. Cap  66  prevents particle flow into the tube  56 . Particles  30  tends to build up in the annulus  60  near the lower check valve  62 , but does not appreciably flow into the tube  56  through the ports  24 ; the design and orientation of the ports  24  prevent sand to flow into the tube  16  (see  FIGS. 4-5 ). 
         [0034]    Advantageously, the fluid in the production tubing is retained while the ESP is off in  FIG. 7 . This allows an almost immediate restart of the ESP and quick return to normal operation ( FIG. 6 ) and production rates. Refilling the production tubing with fluid upon restart of the ESP requires fluid equalization in the tubing and annulus and operation of the ESP in downthrust mode. Repeated startup of the ESP and operation in downthrust mode contributes to shortened ESP runlife. 
         [0035]    The check valve  62  is largely free from impingement by sand  30  during all phases of operation of the device  50 . The check valve  62  in  FIG. 7 , with production ceased, prevents reverse flow of fluids. Such reverse flow would occur through the ESP  14  until hydrostatic equilibrium is achieved between the production tubing and the wellbore. This reverse flow is undesirable because it can cause the ESP  14  to turn in the reverse direction compared to normal operation. The ESP cannot be restarted when it is ‘back spinning’ (turning in a reverse direction)—a period that can sometimes extend for a number of hours. This back spinning causes the operator to wait until he is reasonably assured that the ESP  14  is stationary before attempting to restart the ESP  14 . The distal check valve  62  stops reverse flow, and therefore alleviates this “back spinning” problem. 
         [0036]    In  FIG. 8 , the ESP  14  is turned on (restarted) and there are no significant buildup of particles  30  on top of the ESP discharge, i.e. ports  24  in the tube  56 . The check valve  62  immediately opens upon restart of ESP  14  and production fluid flow through the tube  56  up the production tubing  12  to the surface begins almost immediately. As shown in  FIG. 8 , a number of the ports  24  are not covered by particles  30  and the fluid in the tube  16  flows through the ports  24  into the annulus  60 . The particles  30  cover some of the lower ports  24  (e.g., ports  24  near the lower check valve  62 ) and little fluid flow occurs through these lower ports  24 . However, the density of the particles  30  in the fluid in the annulus decreases towards the surface, allowing some fluid flow through the ports  24  into the annulus  60 . This allows the annulus to be self-clearing. That is, with some ports  24  in the region of distal end  72  uncovered or partially uncovered with particles  30 , fluid flows from the tube  56  through the ports  24  into the annulus  60  helping to clear the remaining sand. 
         [0037]    In the case where sand covers substantially all of the ports  24  in the region of the distal end  72 , the few ports  24  in the region of the proximal end  74  are substantially clear. Restart of ESP  14  in this case causes a pressure differential build-up between the distal and proximal ends  72 ,  74 . In this case, the entire column of sand  30  in the annulus  60  clears through the production tubing  12  almost immediately. In this case, having a large number of ports  24  near the distal end widely spaced from a few ports  24  at the proximal end is advantageous. 
         [0038]      FIG. 9  is a cross sections of the device  50  as shown in  FIG. 6 . In  FIG. 9 , the ESP  14  is operating (e.g., as in  FIG. 6 ) and fluid has traversed from the tube  56  through ports  24  into the annulus  60 . Centralizers  70  end to maintain the position of the tube  56  central in the housing  58 . 
         [0039]      FIG. 10  illustrates an exemplary operational embodiment of the device  50  illustrated schematically in  FIGS. 6-9 . For comparison purposes, like numerals are applied to like components. Generally, end cap  66  is positioned at the proximal end  74  of tube  56 . A few ports  24  are arranged near the end cap  66  to permit fluid flow between the tube  56  and annulus  60 . Centralizers  70  maintain the position of tube  56  in the housing  58 . The check valve  62  is located near the distal end  72 . A large number of ports  24  are positioned through the tube  56  near the distal end  72 . 
         [0040]    While the devices  10 ,  50  are illustrated in the context of a vertical well bore in the figures, it will be understood that horizontal wells can benefit from the use of the devices  10 ,  50 . In fact, horizontal wells make extensive use of proppants for fracking which is a prime contributor to particles in the production tubing which can settle onto an ESP and hinder operation. Additionally, while protection and efficient operation of an ESP are prime uses of the devices  10 ,  50 , other downhole equipment can be protected from particle interference as well.