Patent Publication Number: US-11041350-B2

Title: Mud motor stall protector

Description:
BACKGROUND 
     In the resource recovery industry, mud motors are common devices used to generate torque for uses including drilling among other things. Mud motors utilize the energy of a flowing fluid therethrough to generate rotational torque that is applied in one example to a drill bit. Occasionally the torque created in the mud motor is insufficient to drive the connected tool (e.g. drill bit) through whatever is the target surface. This results in a stall of the mud motor. Fluid flowing through the mud motor without the mud motor rotating changes from a positive operational action to a detrimental one. Specifically, the same flowing fluid that provided the energy for the generation of torque in the rotating mud motor will cause damage to the motor in the form of flow cutting and erosion of sealing surfaces within the mud motor when the motor is not able to rotate due to insufficient torque to overcome the surface against which the connected tool is turning. Such flow cutting and erosion results in delays and increased costs and hence is undesirable to the operator. The art would well receive solutions that avoid such damage. 
     SUMMARY 
     A mud motor stall protector including a housing, a piston translationally disposed in the housing, the piston defining a flow passage therein, and a pin positioned relative to the housing to occupy a portion of the flow passage of the piston or leave the flow passage of the piston open depending upon position of the piston relative to the pin. 
     A mud motor protector including a housing, and a piston disposed within the housing and defining a fluid flow channel therein, the piston being first responsive to a pressure differential across a set of piston seals resulting in piston movement that causes a reduction in flow area in the fluid flow channel of the piston and then responsive primarily to the restriction of the flow area of the fluid flow channel through the piston. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following descriptions should not be considered limiting in any way. With reference to the accompanying drawings, like elements are numbered alike: 
         FIG. 1  is a view of a borehole system in a subsurface formation and having a mud motor stall protector therein; 
         FIG. 2  is a cross section view of a mud motor stall protector as disclosed herein in a closed position; 
         FIG. 3  is the protector of  FIG. 2  in a seal break position; and 
         FIG. 4  is the protector in an open position. 
     
    
    
     DETAILED DESCRIPTION 
     A detailed description of one or more embodiments of the disclosed apparatus and method are presented herein by way of exemplification and not limitation with reference to the Figures. 
     As will be appreciated by one of ordinary skill in the art, and referring to  FIG. 1 , when a mud motor  10  stalls, a rotor of the mud motor cannot turn and hence adopts a fixed position relative to a mud motor stator. In such a condition, fluid flowing through the mud motor  10  is no longer distributed over nearly all of the surface area thereof but rather is restricted to a much smaller pathway through the mud motor  10 . Fluid flow through the mud motor is occasioned by fluid emanating from a pump/source  12 , such as a surface reservoir, at for example, 4 barrels per minute. Such flow rate would not change in a mud motor configuration of the prior art when that motor is in a stalled condition but rather the fluid simply would be pushed through the much smaller pathway. Accordingly, it can be easily seen and has been recognized by the art that flow cutting and erosion are a problem. Addressing this problem by just relieving the fluid pressure with components such as a blow off valve (known in the art) does not resolve the problem. As long as enough fluid still flows in the mud motor, there is a small amount of torque produced on a tool similar to  14  (e.g. drill bit) in  FIG. 1  attached to the mud motor similar to  10  in  FIG. 1  ( FIG. 1  itself is not intended to be a prior art depiction since it illustrates an embodiment of the disclosure hereof as a part of a well system but since appearance Is similar the Figure can also be illustrative of the present discussion). The torque keeps the tool  14  engaged with the surface such as formation  16 ) through which the tool  14  was supposed to be drilling to create a borehole  17 . Reapplication of fluid pressure after the blow off valve vents does nothing to alleviate the engagement and hence the mud motor  10  remains stalled. Rather, according to the teachings hereof, it is necessary that torque be removed from the tool  14  so that the tool  14  will be disengaged from the formation and the drilling operation be restarted upon the reapplication of flowing fluid to the unstalled mud motor. Disengaging the tool  14  from the formation  16  allows the operator to pull up on a string  18  upon which the mud motor  10  and drill bit  14  are operating. Pulling up will release any connection and allow a restart of the motor  10  free of the stall. A mud motor stall protector as taught herein accomplishes this result. 
     Referring to  FIG. 2 , a mud motor stall protector  20  is illustrated. It is to be understood that the mud motor  10  ( FIG. 1 ) is fluidly connected to the protector  20  at the right or downhole side of  FIG. 2 . It is further to be understood that the string  18  ( FIG. 1 ) is connected to the left or uphole side of  FIG. 2 . The string  18  is connected to the source  12  of fluid being pumped to run the mud motor  10  as illustrated in  FIG. 1 . 
     Protector  20  comprises a housing  22  that includes a housing port  24  (two are shown, more or fewer are contemplated) extending between an outer surface  26  of the housing and an inside dimension surface  28 . In an embodiment, the housing also defines two additional inside surfaces  30  and  32 . Inside surface  30  is of a diameter smaller than the diameter of the inside surface  28 . A piston  34  is shaped to communicate with the surfaces  30  and  28  through seals  36  and  38 . The piston is also shaped to communicate with surface  32  through seal  40 . The communications and their effects are discussed hereunder. The piston  34  defines a flow passage  42  and an opening  44  (three visible but more or fewer contemplated) that is alignable or misalignable with the port  24  depending upon the position of the piston  34 . The piston  34  further includes a nozzle  46  that may be formed within the piston or may be a separate component that is disposed in sealed relationship with the piston  34 . The nozzle defines a fluid conduit  47  that supplies fluid to flow passage  42  during use. In an embodiment, a biasing member  48  such as a spring is disposed between a piston shoulder  50  and a housing shoulder  52 . The spring  48  is a compression spring that will urge the piston back to a closed position (shown in  FIG. 2 ) when pressure activation forces are insufficient to keep the piston in the open position ( FIGS. 3 and 4 ). Connected to the housing is a protector sub  54 . The sub  54  in an embodiment supports a pin  56  that extends into the piston flow passage  42  and depending upon piston position, extends into the nozzle  46 , reducing a flow area therethrough. The protector sub  54  also includes a supply channel  58  (two shown but more or fewer contemplated) that supplies fluid to the mud motor  10  attached to the downhole end of the protector  20  as noted above. 
     Having described all of the parts of the protector  20  above, its operation is here addressed. Due to the surfaces  30  and  28  being of differing diameter, a differential piston area is created between the seals  36  and  38 . Accordingly, when pressure is applied to the seals  36  and  38  through opening  44  and from a volume  60 , the differential piston areas will cause the piston  34  to move. The pressure increase that piston  34  is designed to respond to is related to a motor stall. Specifically, when the motor  10  stalls and the flow therethrough becomes labored, the pressure of the fluid being supplied thereto through protector sub  54  increases (since it is being pumped from a remote location and now suddenly cannot flow as easily through the mud motor  10 ). That pressure exists through the fluid in volume  60  and through openings  44  and in the piston flow passage  42  for example. This pressure thus acts on the seals  36  and  38  as described. The piston  34  will then move as described, that movement being toward the right side of  FIG. 2 . This latter condition is illustrated in  FIG. 3 , to which reference is encouraged. 
     Referring to  FIG. 3 , the piston  34  has moved to being the opening  44  closer to alignment with port  24  but the more significant change is that the piston  34  has moved to a position where the pin  56  occupies at least a portion of the fluid conduit  47  of the nozzle  46 . One of ordinary skill in the art will appreciate that a flow area otherwise defined within fluid conduit  47  when open will be significantly restricted when the pin  56  is at least partially occupying the fluid conduit  47 . As this is not a seal, fluid will still flow past the restriction  62  but the pressure of the fluid (flowing from left of Figure) will be substantially higher upstream (to the left) of the restriction  62  than it is downstream (to the right) of the restriction  62 . The piston  34  while initially being responsive to the differential pressure at seals  36  and  38 , will at the point the restriction  62  is made be instead responsive to differential pressure across the restriction. This is not to say that the pressure differential across seals  36  and  38  disappears, but rather only that the pressure differential across restriction  62  represents a greater impetus on the piston  34  and hence eclipses the activity of the pressure differential across seals  36  and  38 . In view hereof, the piston  34  will move even more downstream (to the right of Figure) thereby aligning the opening  44  with the port  24 , and causing the pin  56  to occupy even more of the conduit  47  as illustrated in  FIG. 4 . Pressure in the volume  60  is vented to annulus  64  in this position allowing the tool  14  to disengage with the formation  16  so that the string  18  may be lifted and the motor  10  restarted. Because the restriction  62  maintains the piston in the opening and port aligned condition regardless of pressure caused by the stall, the piston  34  does not cycle like those in the prior art in an endless effort to free the tool  14  that will never happen. Rather, the fluid pressure is nearly all removed from the tool ensuring disengagement from the work surface enabling lift up and restart. Upon disengagement, the pumps are shut down which allows the piston  34  to be reset by spring  48  so that renewed fluid flow will restart the motor without the encumbrance of the stall. 
     The protector  20  disclosed herein ensures reduced erosional damage to a mud motor  10  because the protector automatically continues to keep the motor free of fluid flow until the pumps  12  are shut down. Hence the delay of which those of skill in the art are painfully aware between the onset of a stall and the recognition of that fact resulting in the shutting down of pumps  12  has no additional deleterious effect on the mud motor since the protector  20  maintains the motor  10  in the safe condition until the pumps are actually shut down due to the fact that the protector piston  34  cannot reset until the pumps  12  are shut down and pressure and flow upstream of the protector  20  have ceased. 
     Set forth below are some embodiments of the foregoing disclosure: 
     Embodiment 1: A mud motor stall protector including a housing, a piston translationally disposed in the housing, the piston defining a flow passage therein, and a pin positioned relative to the housing to occupy a portion of the flow passage of the piston or leave the flow passage of the piston open depending upon position of the piston relative to the pin. 
     Embodiment 2: The protector as in any prior embodiment wherein the housing further includes a port extending from an inside surface of the housing to an outside surface of the housing. 
     Embodiment 3: The protector as in any prior embodiment wherein the piston includes an opening alignable or misalignable with the housing port depending upon position of the piston within the housing. 
     Embodiment 4: The protector as in any prior embodiment wherein the housing further defines at least two inside dimension areas. 
     Embodiment 5: The protector as in any prior embodiment wherein the at least two areas are on opposing sides of a port extending from an inside surface of the housing to an outside surface of the housing. 
     Embodiment 6: The protector as in any prior embodiment wherein the at least two areas create, with the piston, a differential piston area that causes the piston to translate during use of the protector based upon exposure to a threshold pressure. 
     Embodiment 7: The protector as in any prior embodiment wherein the threshold pressure is associated with a stall of a mud motor operably attached to the protector. 
     Embodiment 8: The protector as in any prior embodiment wherein the housing defines three inside dimension areas. 
     Embodiment 9: The protector as in any prior embodiment wherein the piston further includes a nozzle. 
     Embodiment 10: The protector as in any prior embodiment wherein the pin and the piston, when the pin occupies a portion of a fluid conduit of a nozzle of the piston, create a pressure drop in flowing fluid. 
     Embodiment 11: The protector as in any prior embodiment wherein the pressure drop urges the piston to a position where a piston opening is aligned with a housing port. 
     Embodiment 12: The protector as in any prior embodiment wherein pressure drop urges the piston against a reset spring. 
     Embodiment 13: The protector as in any prior embodiment further comprising a protector sub attached to the housing and supporting the pin. 
     Embodiment 14: The protector as in any prior embodiment wherein the protector sub includes supply channels that supply fluid to a mud motor. 
     Embodiment 15: A mud motor protector including a housing, and a piston disposed within the housing and defining a fluid flow channel therein, the piston being first responsive to a pressure differential across a set of piston seals resulting in piston movement that causes a reduction in flow area in the fluid flow channel of the piston and then responsive primarily to the restriction of the flow area of the fluid flow channel through the piston. 
     Embodiment 16: The protector as in any prior embodiment wherein a pin fixed relative to the housing, when occupying a portion of the fluid flow channel of the piston causes the reduction in flow area. 
     Embodiment 17: A mud motor system including a mud motor, and a mud motor protector as in any prior embodiment fluidly connected to the mud motor. 
     Embodiment 18: A mud motor system including a mud motor, and a mud motor protector as in any prior embodiment fluidly connected to the mud motor. 
     Embodiment 19: A well system including a borehole in a subsurface formation, a string disposed in the borehole, a mud motor protector as in any prior embodiment connected to the string, and a mud motor fluidly connected to the mud motor protector. 
     Embodiment 20: A well system including a borehole in a subsurface formation, a string disposed in the borehole, a mud motor protector as in any prior embodiment connected to the string; and a mud motor fluidly connected to the mud motor protector. 
     The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. Further, it should be noted that the terms “first,” “second,” and the like herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. The modifier “about” used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (e.g., it includes the degree of error associated with measurement of the particular quantity). 
     While the invention has been described with reference to an exemplary embodiment or embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the claims. Also, in the drawings and the description, there have been disclosed exemplary embodiments of the invention and, although specific terms may have been employed, they are unless otherwise stated used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention therefore not being so limited.