Patent Publication Number: US-10787885-B2

Title: Upstream shuttle valve for use with progressive cavity pump

Description:
FIELD 
     The present disclosure relates to a shuttle valve and more particularly for a shuttle valve for use with a downhole progressive cavity pump system. 
     BACKGROUND 
     The subject of the present disclosure relates generally to downhole wellbore systems used for pumping hydrocarbon products to surface. Such systems are often called artificial lift systems. The present systems typically use a progressive cavity (PC) pump to pump liquid hydrocarbon from underground formations in a cased wellbore up to surface. The stator portion of the PC pump is typically run down on a tubing string and the rotor portion of the PC pump is run into the stator on a rod string. Fluid is pumped through the tubing string to surface. A fluid column is also present in the annulus between the tubing string and the wellbore casing. 
     In many artificial lift operations, steady power supply is a problem and power failures are common. When power to a PC pump motor is lost and the PC pump fails to pump fluid, fluid level within the tubing string drops to a level equal to the fluid level in the tubing-casing annulus. This causes a number of problems, the first of which the need for a lengthy re-start up time when power to the PC pump motor is eventually restored, since fluid level within the tubing string must again be pumped back up to surface. Further re-start up time is required to get production rates back to where they were prior to the power failure. In some cases re-start up time can result in the loss of several days of production time. 
     A second problem with PC pump shut down is that gases that are entrained in the high pressure fluid being pumped and migrate into the elastomeric material otherwise known as gas impregnation. Gas molecules then expand or deform the elastomeric material once it is no longer pressurized by pumping. The released gas bubbles tend to migrate into the elastomeric material of the PC pump stator and cause bulging and warping of the shape of the stator profile also known as explosive decompression in elastomeric compounds. When power is restored and the PC pump is run again, the rotor no longer fits properly in the warped and bulging stator and rotation of the rotor tends to gouge out parts of the stator material. This causes a number of problems in production, blockage within the tubing and of course equipment damage. 
     To avoid loss of fluid level in the tubing string during power failures and PC pump shut down, it is known to place a check valve downstream of the PC pump, to allow upstream flow during operation, but to prevent downstream flow back into the formation during PC pump shut down. An example of such a downstream check valve can be seen in US 2011/0259438, inventor Lawrence Osborne. 
     Downstream check valves can cause issues when running the rotor portion of the PC pump down on the rod string into the stator portion of the PC pump. Since the check valve prevents flow of fluid downstream, fluid in the stator cavity cannot be displaced when the rotor is being run in, causing difficulty in installing the rotor and improper alignment of the rotor within the stator. Downstream check valves also present flow restrictions at the PC pump intake. 
     While a prior art upstream check valve can be seen in WO/2015075636, owned by Serinpet of Colombia, this check valve is operated on inertial mass and requires an enlarged tubing string ID surrounding the valve to overcome flow losses as fluid passes around the check valve and travels upstream to surface. 
     There is therefore a need to design a flow restriction system that prevents fluid level losses in artificial lift applications that is easy to install, reduces flow losses, and does not require special equipment. There is also a need to provide flow restriction systems with improved sealing to ensure lack of back flow and having a centralized design for deviated or horizontal wells. 
     SUMMARY OF THE INVENTION 
     An artificial lift system is provided for use for pumping fluid from a downhole wellbore to surface. The system comprises a progressive cavity pump, said progressive cavity pump comprising a stator run on a tubing string and a rotor run on a rod string into the stator and a shuttle valve positioned upstream of the progressive cavity pump, wherein said shuttle valve comprises a non-weighted shuttle and wherein said non-weighted shuttle is moveable axially within said shuttle valve from force of fluid alone. 
     An upstream shuttle valve is further provided for use upstream of a progressive cavity pump, wherein said shuttle valve comprises a non-weighted shuttle that is moveable axially within said shuttle valve from a force of fluid alone, to open and close the shuttle valve. 
     A method is further still provided for pumping fluid from a wellbore in an artificial lifts system. The method comprises the steps of providing a progressive cavity pump; providing a shuttle valve upstream of the progressive cavity pump, said shuttle valve comprising a non-weighted shuttle axially moveable within the shuttle valve; opening the shuttle valve to allow flow of fluid upstream from the progressive cavity pump, through the shuttle valve when the progressive cavity pump is pumping; closing the shuttle valve to prevent flow of fluid downstream through the shuttle valve when the progressive cavity pump is stopped, wherein opening and closing of the shuttle valve is performed by moving the shuttle axially from force of fluid flow alone. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a down hole well with a PC pump and one embodiment of the shuttle valve of the present invention; 
         FIG. 2 a    is an elevation view of one embodiment of the shuttle valve of the present invention; 
         FIG. 2 b    is a cross-sectional view of the embodiment of the shuttle valve of  FIG. 1   a;    
         FIG. 3 a    is a top perspective view of one embodiment of the shuttle valve of the present invention, depicting fluid flow as it bypasses the shuttle valve; 
         FIG. 3 b    is a cross-sectional detail of a portion of the shuttle valve of the present invention, depicting fluid flow as it bypasses the shuttle valve; 
         FIG. 4  is a graphical depiction of pressure drop as a function of oil viscosity, as fluid bypasses the shuttle valve of the present invention; 
         FIG. 5 a    is an elevation view of one embodiment of the shuttle valve of the present invention; 
         FIGS. 5 b  to 5 e    are cross-sectional views of one embodiment of the shuttle valve of the present invention in various statues of use; 
         FIGS. 6 a  and 6 b    are cross sectional views of one embodiment of an optional pull rod for use with the shuttle valve of the present invention; 
         FIG. 7  is a perspective view of a rod sting having an embodiment of the shuttle valve of the present invention, a mandrel and a pull rod “no go” installed thereon; 
         FIG. 8  is a bottom perspective view of a mandrel for use with one embodiment of the shuttle valve of the present invention; 
         FIG. 9  is a cross-sectional elevation view of one embodiment of the shuttle valve of the present invention and a seating mandrel installed on a rod string; 
         FIG. 10  is a detailed top perspective view of one embodiment of the shuttle valve of the present invention, showing the discharge ports; 
         FIG. 11  is a detailed cross-sectional elevation view of one embodiment of the shuttle valve of the present invention; 
         FIG. 12  is a detailed cross-sectional elevation view of the shuttle of one embodiment of the shuttle valve of the present invention; and 
         FIG. 13  is a bottom plan view of one embodiment of the shuttle valve of the present invention, showing a pull rod “no go”. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
     The present disclosure relates to an improved device and method for preventing fluid loss from a tubular string in an artificial lift system. 
     It is understood that the improved device disclosed herein is not limited in its application to the details of the construction and arrangement of the parts illustrated in the accompanying drawings. The device disclosed herein is capable of other embodiments and configurations and of being practiced or carried out in a variety of ways, and the terminology employed herein are for the purposes of description only and are not intended to be limiting in any way. 
     Moreover, in interpreting both the specification and the claims, all terms should be interpreted in the broadest possible manner consistent with the context. In particular, the terms “comprises” and “comprising” should be interpreted as referring to elements, components, or steps in a non-exclusive manner, indicating that the referenced elements, phases, or steps may be present, or utilized, or combined with other elements, phases, or steps that are not expressly referenced. 
     More particularly, the invention relates to a shuttle valve that is used upstream of a PC pump to prevent loss of fluid back down into the well and PC pump backspin, should the PC pump stop working. The shuttle valve also serves to reduce start up time, by maintaining fluid levels in the well when the PC pump re-starts pumping. The present shuttle valve allows flow upstream to the surface, but prevents flow downstream. The present invention further provides three distinct sealing areas within the shuttle valve system. Multiple sealing areas in both the shuttle valve  22  and surrounding equipment ensure no leakage between sections of the shuttle valve system. In securing against leaks, fluid losses are minimized. 
     With reference to  FIG. 1 , a cased  2  wellbore is depicted. A tubing string  4  run into the cased hole  2  and anchored in place by tubing anchor  6 . The tubing string  4  comprises a stator portion  8  of a PC pump  14  and also a seating nipple  18 . A rod string  10  is run down inside the tubing string  4 , the rod string  10  comprising, from bottom to top: a rotor portion  12  of the PC pump  14 ; one or more optional flexible rod segments  16 ; a seating mandrel  20  that sits in the seating nipple  18  and comprises the shuttle valve  22 ; an optional rod torque anchor  24  and an optional bearing box  26 . 
     A tag bar  30  at the lowest end of the tubing string  4 , or other means well known in the art, may be used for locating the rotor  12  inside the stator  8 . 
     The seating mandrel  20  fits into the nipple  18  with an interference fit with close tolerances. The fit is designed to hold pressures through the mechanical seal between the seating mandrel  20  and the nipple  18 . 
     In a further embodiment, the seating mandrel  20  is surrounded by a sealing sleeve  60 , as depicted in  FIG. 1 . The sealing sleeve  60  is preferably made from a non-metallic, non-elastomeric material that seals into the seating nipple  18  to create a friction seal and barrier. The sealing sleeve  60  is most preferably made from Teflon™. The non-metallic, non-elastomeric material of the sealing sleeve  60  ensures that it is non-deforming and allows that the seating mandrel  20  can be sealed into the seating nipple  18  with a pressure or force and can be unsealed by releasing an equal pressure, without deforming the seating mandrel  20 . 
     A problem with prior art downstream check valves is that when the rotor part of the PC pump is run down on the rod through the tubing string and into the stator part of the PC pump, the rotor necessarily displaces fluid that was in the stator, but a downstream check valve does not allow that fluid to displace downwardly, leading to a misalignment of the rotor inside the stator. Furthermore, downstream check valves form intake restrictions as fluid needs to displace the ball of the check valve under pressure in order to allow flow into the suction of the pump. Since all wells are under pressure, this results in downstream check valves becoming actuated, and undesirably hindering pump performance. 
     In the present invention, as illustrated in  FIG. 1 , the present shuttle valve  22  is located upstream of the PC pump  14  and therefore does not check flow downstream at the PC pump  14 , thereby allowing the necessary displacement of fluid downstream from an inside cavity of the stator  8  when the rotor  12  is inserted. 
     Further details of the shuttle valve of the present invention are now presented, with reference to  FIGS. 2 a    to  13 . 
     The present shuttle valve  22  comprises an outer housing  32  that is connected to the seating mandrel  20  that sits in the seating nipple  18 . The housing  32  is rotationally coupled to the rod  10 , to allow the rod  10  to spin and operate the rotor  12 . The shuttle rotates with the inertia of the spinning rod  10 . The coupling is preferably a first bushing  34 , said first bushing  34  more preferably being made from a high temperature and high wear rating material, most preferably a nano-tube carbon composite, although any other materials known in the art with similar high temperature and wear resistance would be suitable for the purposes of the present invention. The first bushing is preferably designed to have close tolerances to both rod  10  and shuttle valve  22 , while also having enough space for the shuttle valve  22  to actuate. The first bushing  34  further preferably acts as a mechanical seal to an internal part of the shuttle valve  22 . One or more vents  36  allow fluid bypassing the shuttle valve  22  to travel upstream through the tubing string  4  to surface. 
     The present shuttle  38  seals against the rod  10  using a mechanical seal design that restricts fluid by-pass and still allows for shuttle actuation along the rod  10  based on fluid moving in either direction. This mechanical seal, formed by the continuous contact between the shuttle  38  and the rod  10  is one complete seal assembly and, unlike the prior art, does not consist of several O-ring seals or other redundant seals that can cause excess friction or deform and restrict movement of the shuttle  38 . This form of continuous single mechanical seal operates on an inside of the shuttle  38  and creates virtually no drag or friction between the shuttle  38  and the rod  10 . 
     The shuttle  38  of the shuttle valve  22  is both rotationally and axially moveable about the rod  10 . This allows the rod  10  to rotate as it drives the rotor  12 , and also allows the shuttle  38  to move up and down axially to open and close the shuttle valve  22 . Rotational and axial movement is preferably accommodated through the second bushing  40 , said second bushing  40  having similar wear and temperature resistance to the first bushing  34  and more preferably being made from similar materials to the first busing  34 . 
     The shuttle  38  is preferably made from abrasion resistant, lightweight materials that both withstand harsh impact from sand particulate in the oil stream being pumped and also minimize flow losses as fluid bypasses the shuttle valve  22  and travels upstream. More preferably, the shuttle  38  is made from ceramics such as zirconium ceramic, although it would be well understood by a person of skill in the art that other materials could also be used without departing from the scope of the invention. 
     The present shuttle valve  22  is designed to minimize flow losses around it when fluid is pumped up from the PC pump  14 , past the check valve  22  and up to surface. Flow losses are minimized by the unique shape of the shuttle  38 . The shuttle  38  comprises a small outside diameter (OD) cylindrical upper portion  42  that flares into a cylindrical mid-section  44 , said mid-section  44  having a larger OD than the upper portion  42 , and tapers to a conical lower end  46 . 
     The conical lower end  46  shape and the lightweight of the present shuttle  38  results in the shuttle not requiring a great deal of upward flow to lift the shuttle  38  off of cooperating seat  48 . The lower end  46  of the shuttle  38  and the seat  48  preferably share a common angle of inclination to allow a good fit, while also preventing the shuttle  38  from deforming into or otherwise getting stuck in the seat  48 . Hence the shuttle  38  requires very little upwards fluid flow to open the shuttle valve  22  from a closed position. Since the present shuttle  38  is preferably made from lightweight materials, it allows the shuttle  38  to move axially up and down by force of the flowing fluid alone, with no additional mechanisms needed. 
     With reference to  FIGS. 3 a , 3 b    and  4 , flow patterns of the pumped oil around the present shuttle valve  22  can be seen, in which darker lines represent compressive forces, or pressure losses and lighter lines show laminar flow with little to no pressure losses. It can be seen in both  FIGS. 3 a  and 3 b    that flow losses are minimized to the areas just before and just after the shuttle  38 . Around the shuttle  38  itself, the flow is laminar and with very low pressure losses. Furthermore, since the flow is laminar around the shuttle  38 , undesirable re-circulation of fluids around profiles of the shuttle valve  22  are minimized. 
     With reference to  FIG. 4 , it can be seen that the maximum pressure drop across the present shuttle valve  22 , corresponding with a typical maximum oil viscosity (8 API w/10,000 cps oil @1,000 bpd) is only about &lt;35 psi, which is also quite low. These low pressure drops, low flow losses and the laminar flow regime around the present shuttle valve  22  are all achieved without the need to widen the ID of the tubing string  4  around the shuttle valve  22 . Thus the present shuttle valve  22  can be run into a standard section of tubing string  4 , with no loss in the tubing string-casing annular area  100 . 
     The unique flare from the upper end  42  to the mid-section  44  of the present shuttle  38  advantageously forms a ledge  50 . In the event of a PC pump  14  shut down, all that is required to close the shuttle valve  22  is the force of the downward flow of fluid in the tubing string  4  acting on this ledge  50  to seat shuttle  38  against seat  48 , as seen in  FIG. 5 d   . This allows for efficient closure of the shuttle valve  22  without the need for a weighted shuttle or ball, as seen in many prior art check valves, nor the need for springs or other mechanisms to aid in seating the shuttle or ball. Low friction from second bushing  40  further aids in efficiently lowering shuttle  38  onto seat  48 . 
     Since the present shuttle  38  is not weighted, no extra work is needed by the PC pump  14  to lift the shuttle  38  off of the seat  48  during re-start up, or to keep the shuttle valve  22  in the open position during normal operation, as seen in  FIGS. 5 b    and  5   c.    
     The shuttle  38  preferably comprises one or more grooves  52  formed into the mid-section  44 . These recessed grooves  52  serve to catch any particulate in the oil being pumped, thereby preventing particulate from building up on the surface of the shuttle  38  and potentially restricting the flow path of fluid around the shuttle  38 . Preferably, the grooves  52  are angled to match a potential angle of the fluid flow as to moves upwards, thus allowing potentially swirling fluid flow around the shuttle  38  without rotating the shuttle  38  itself. 
     Further preferably, any particulate that catches on the seat  48  of the shuttle valve  22  is advantageously scraped down and away when the shuttle  38  seats itself on the seat  48 , thereby minimizing particle build up on the seat  48 . 
     The present invention thus provides three separate sealing areas to ensure that the shuttle valve restricts fluid flow when required. Namely, the present system provides sealing between the shuttle  38  and the seat  48 ; between the seating mandrel  20  and the seating nipple  18  and between the shuttle valve  22  and the rod string  10 . 
     In the event that shuttle actuation fails for any reason, the present seating mandrel  20  can be removed via the non-deforming seating sleeve  60 , then the unit brought to the surface, replaced and run downhole again. 
     The present shuttle valve system further presents a means of reducing failures in artificial lift systems due to deviated or un-centered drive rods. In deviated or horizontal wells, the tubing string  4  is commonly able to accommodate the well bore deviations and angles due some inherent flexibility in the tubing material. As the drive rod string  10  is installed inside the tubing string, it too has a degree of flexibility to accommodate the various angles or dog leg severity, also called “DLS”. However, as the PC pump  14  begins to operate, the rod string  10  is put into tension as the weight of the fluid produced creates hydrostatic head and flow losses pull on the rod to place it under tension. The rod string  10  under tension loses its flexibility and cannot remain follow the bends and DSL required to stay centered inside the tubing string  4 . Instead, the rod string  10  under tension tends to take the straightest route through the well. As the rod string  10  rotates in PC pump operation, it tends to rub against the inside diameter of the tubing string  4  and tubing and rod string wear lead to failure in the PC pumping wells. 
     The present shuttle valve  22  is designed to operate in deviated wells as the shuttle&#39;s minimal movement required for actuation allows it to operate in confined areas. Furthermore, advantageously, the rod string  10  itself is centered by the seating mandrel  20 . The seating mandrel  20  when seated on the seating nipple  18  is automatically centered within the tubing string  4 . By centering the seating mandrel  20  in the seating nipple  18 , the seating mandrel  20  in turn centers the rod string  10  within the tubing string  4 . Furthermore, in any deviation or horizontal application the shuttle  38  and seat  48  always remain centered and can operate properly. Also the sealing sleeve  60  of the seating mandrel  20  is flexible to accommodate deflection and allows for adjustment for harsher deviated well bore geometries. More preferably the seating mandrel  20  can be made from a material with sufficient strength so as not to wear out when side-loading forces on the rod string  10  causing any rubbing of the rod string  10  against an inner surface of seating mandrel  20 . 
     With reference to  FIGS. 6 a  and 6 b   , a pull rod no-go  54  is shown that is used to keep the shuttle valve in the open position when the entire rod string  10  is being pulled out of the tubing string  4 . The pull rod “no-go”  54  is used for two functions: firstly to remove the entire system from the well during a work over; and secondly for flushing the system in the event that the well requires a circulation treatment. The “no-go”  54  connects to the shuttle valve  22  by lifting the rod string  10  up to surface until contact is made between the “no-go”  54  and the shuttle valve  22 ; contact weight indicators on the rig further preferably allow for contact visibility. The distance at which the “no-go”  54  is placed on the rod string  10  below the shuttle valve  22  is preferably pre-measured to allow for the rotor  12  to be completely removed from the stator  8 . As well, the “no-go”  54  will release the shuttle valve  22  by contacting the shuttle  38  below the seat  48 , thus lifting the shuttle  38  off its seat  48  and releasing the fluid above. Fluid will then flow past the shuttle  38  or it can be pumped past the shuttle  38  to stimulate the well bore. 
     As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations and modifications are possible in the practice of this invention without departing from the spirit or scope thereof. Accordingly, the scope of the invention is to be construed in accordance with the substance defined by the following claims.