Patent Publication Number: US-11391114-B2

Title: Pressure compensation piston for dynamic seal pressure differential minimization

Description:
BACKGROUND 
     Directional drilling in oil and gas exploration and production has been used to reach subterranean destinations or formations with a drilling string. One type of directional drilling involves rotary steerable drilling systems that allow a drill string to rotate continuously while steering the drill string to a desired target location in a subterranean formation. Rotary steerable drilling systems are generally positioned at a lower end of the drill string and typically include a rotating drill shaft or mandrel, a housing that supports the rotating drill shaft, and additional components that seal a space between the housing and the rotating drill shaft from entry of drilling fluids and other debris. Under normal operating conditions, a pressure differential exists between the annulus pressure and the tool pressure, requiring a specialized rotary seal assembly. 
    
    
     
       BRIEF DESCRIPTION 
       Reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  depicts a well system including an exemplary operating environment that the apparatuses, systems and methods disclosed herein may be employed; 
         FIG. 2  depicts one embodiment of a pressure compensation piston according to principles of the disclosure, as might be used with a rotary seal assembly; 
         FIG. 3  depicts one embodiment of a rotary seal assembly according to one or more principles of the disclosure; and 
         FIG. 4  depicts another embodiment of a rotary seal assembly according to one or more other principles of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In the drawings and descriptions that follow, like parts are typically marked throughout the specification and drawings with the same reference numerals, respectively. The drawn figures are not necessarily to scale. Certain features of the disclosure may be shown exaggerated in scale or in somewhat schematic form and some details of certain elements may not be shown in the interest of clarity and conciseness. The present disclosure may be implemented in embodiments of different forms. 
     Specific embodiments are described in detail and are shown in the drawings, with the understanding that the present disclosure is to be considered an exemplification of the principles of the disclosure, and is not intended to limit the disclosure to that illustrated and described herein. It is to be fully recognized that the different teachings of the embodiments discussed herein may be employed separately or in any suitable combination to produce desired results. 
     Unless otherwise specified, use of the terms “connect,” “engage,” “couple,” “attach,” or any other like term describing an interaction between elements is not meant to limit the interaction to direct interaction between the elements and may also include indirect interaction between the elements described. 
     Unless otherwise specified, use of the terms “up,” “upper,” “upward,” “uphole,” “upstream,” or other like terms shall be construed as generally toward the surface of the ground; likewise, use of the terms “down,” “lower,” “downward,” “downhole,” or other like terms shall be construed as generally toward the bottom, terminal end of a well, regardless of the wellbore orientation. Use of any one or more of the foregoing terms shall not be construed as denoting positions along a perfectly vertical axis. Unless otherwise specified, use of the term “subterranean formation” shall be construed as encompassing both areas below exposed earth and areas below earth covered by water such as ocean or fresh water. 
     Disclosed, in one embodiment, is a pressure compensation piston for use with a rotary seal assembly. The pressure compensation piston, in one embodiment, may be a stepped piston which rotates relative to a rotatable shaft, while sliding longitudinally along the shaft to compensate for pressure changes that may occur as the rotatable shaft moves downhole in a wellbore. The pressure compensation piston may be used to adjust pressure across a dynamic rotary seal, and in some embodiments may compensate for a high bore pressure and low annulus pressure, as will be discussed herein with calculation examples. 
     In another embodiment, there is disclosed a rotary seal assembly which may be used with a motor, such as a progressive displacement motor, or mud motor, downhole in a wellbore. The rotary seal assembly may include, in some embodiments, a housing, and a rotatable shaft positioned in a longitudinal opening in the housing, the housing and rotatable shaft forming a cavity there between. Within the cavity may be a radial bearing and a pressure compensation piston, wherein the pressure compensation piston is configured to slide longitudinally relative to the housing. A first dynamic rotary seal may seal the pressure compensation piston relative to the rotatable shaft, and a second dynamic rotary seal may seal the housing relative to the rotatable shaft. In some embodiments, the rotary seal assembly may include an annulus pressure port in the housing, the annulus pressure port configured to couple a pressure source outside of the housing to a stepped up area of the stepped piston. 
     Referring to  FIG. 1 , depicted is a well system  100  including an exemplary operating environment that the apparatuses, systems and methods disclosed herein may be employed. The well system  100  is illustrated with a wellbore  110  drilled into the earth  115  from the ground&#39;s surface  120  using a drill bit  130  provided on a conveyance  140 . For illustrative purposes, the top portion of the wellbore  110  includes surface casing  150 , which is typically at least partially comprised of cement and which defines and stabilizes the wellbore  110  after being drilled. The wellbore  110  also may include intermediate casings (not shown), which may be stabilized with cement. The cement performs several functions, including preventing wellbore collapse, maintaining a physical separation between the Earth&#39;s layers, providing a barrier to prevent fluid migration, enhancing safety, and protecting the Earth&#39;s layers from any contaminants introduced during open-hole operations, or the like. 
     The drill bit  130  is located proximate the bottom, distal end of the conveyance  140  that supports various components along its length. During open-hole operations, the drill bit  130  and the conveyance  140  are advanced into the earth  115  by a drilling rig  160 . The drilling rig  160  may be supported directly on land as illustrated, or on an intermediate platform if at sea. 
     The drill bit  140  may be coupled with a motor, and may further include a rotary seal assembly  170 . The rotary seal assembly  170  may include embodiments of a pressure compensation piston configured to lower pressure across the rotary seal assembly  170 . Lowering pressure across the rotary seal assembly  170  may lower fluid loss from the bore to the annulus that may hinder or lesson performance of tools positioned downhole of the rotary seal assembly  170 . Certain dynamic rotary seals which may be used in the rotary seal assembly may be configured to withstand certain maximum pressure amounts before function and performance of the dynamic rotary seal may be impaired. Once such seal is a Kalsi seal, as might be purchased from Kalsi Engineering, 745 Park Two Drive, Sugar Land, Tex. 77478. As such, there is a need to reduce pressure acting on certain dynamic rotary seals, such as the Kalsi seal, in order to maintain expected performance of the dynamic rotary seal and prevent failure. 
     The wellbore  110 , which is illustrated extending downhole into the Earth&#39;s layers, and any components inside the wellbore  110  are subjected to hydrostatic pressure originating from subterranean destinations or formations. The hydrostatic pressure acting on the conveyance  140  provided inside the wellbore  110  is identified as formation hydrostatic pressure. The hydrostatic pressure originating from within the conveyance  140  is identified as backpressure hydrostatic pressure. As the drilling depth increases, a hydrostatic pressure differential may develop between the outside formation hydrostatic pressure and the backpressure hydrostatic pressure. 
     Referring to  FIG. 2 , depicted is one embodiment of a pressure compensation piston  200  for use with a rotary seal assembly placed downhole in a wellbore, such as the rotary seal assembly  170  shown in  FIG. 1 . The pressure compensation piston  200  may be configured to lower the differential pressure over the rotary seal assembly. In some embodiments, the pressure compensation piston  200  may be a stepped piston  205  having an opening extending there through for positioning the stepped piston  205  about a rotatable shaft  210  of a rotary seal assembly. In this embodiment, a rotary seal  215  may be positioned along a radial surface of the opening for sealing the stepped piston  205  relative to the rotatable shaft  210 . 
     In some embodiments, one or more linear dynamic seals  220  may be positioned about the stepped piston  205  for sealing the stepped piston  205  relative to a housing surrounding the pressure compensation piston  200 . In some embodiments, the one or more linear dynamic seals  220  may be fixed location seals. 
     The stepped piston  205  may slide longitudinally (left-right) when acted upon by wellbore pressure and annulus pressure external to the pressure compensation piston  200 . The stepped piston  205  may thereby lesson dynamic pressure acting on the dynamic rotary seal  215  and reduce the likelihood of failure over time. The fluid loss from the wellbore may then be reduced and lessen any impact the fluid may have on the performance of tools in the wellbore downhole of the pressure compensation piston  200 . 
     In some embodiments, the opening through the stepped piston  205  may include a diameter (D 0 ). Located in the diameter (D 0 ), in certain embodiments, is a circumferential profile  225  extending radially outward into the stepped piston  205 . In this embodiment, the dynamic rotary seal  215  may be positioned within the circumferential profile  225 . The stepped piston  205  may also include a first diameter (D 1 ) or first step portion and a second greater diameter (D 2 ) or second step portion, and in this embodiment, the circumferential profile  225  may be located in the first diameter (D 1 ) portion. While the circumferential profile  225  is located in the first diameter (D 1 ) portion in the illustrated embodiment of  FIG. 2 , other embodiments may exist wherein the circumferential profile  225  is located in the second diameter (D 2 ) portion. 
     Referring now to  FIG. 3 , depicted is an embodiment of a rotary seal assembly  300  designed, manufactured and operated according to the disclosure, which may be used with a motor, such as, e.g., a mud motor. In this embodiment, the rotary seal assembly  300  includes a pressure compensation piston  305  which may be positioned in a cavity  310  formed between a housing  315  and a rotatable shaft  320 . The rotatable shaft  320 , in the illustrated embodiment, is positioned in a longitudinal opening in the housing  315 . The pressure compensation piston  305  may be a stepped piston, similar to stepped piston  205 , having an opening extending there through for positioning the pressure compensation piston  305  about the rotatable shaft  320 . In some embodiments, the pressure compensation piston  305  may be configured to slide longitudinally (left to right) within the cavity  310  with respect to the housing  315  in response to pressure acting upon the pressure compensation piston  305 . The pressure acting upon the pressure compensation piston  305 , in some embodiments, may be bore pressure and/or annulus pressure, in certain embodiments. 
     In some embodiments, a first dynamic rotary seal  325  may be positioned along a radial surface of the opening within the pressure compensation piston  305 , for sealing the pressure compensation piston  305  relative to the rotatable shaft  320 . In some embodiments, the pressure compensation piston  305  and the housing  315  may be rotationally fixed relative to each other. In some embodiments, there may be a first linear dynamic seal  330  positioned at least partially within a radially exterior surface of the first diameter (D 1 ) portion, to seal the first diameter (D 1 ) portion relative to the housing  315 . In other embodiments, there may be a second linear dynamic seal  335  positioned at least partially within a radially exterior surface of the second diameter (D 2 ) portion, to seal the second diameter (D 2 ) portion relative to the housing  315 . 
     The pressure compensation piston  305  and the housing  315  may rotate relative to the rotatable shaft  320 , and in this embodiment, a second dynamic rotary seal  340  may be positioned proximate and between an outer radial surface of the rotatable shaft  320  and an inner radial surface of the longitudinal opening of the housing  315 , for sealing the rotatable shaft  320  relative to the housing  315 . 
     In some embodiments, the housing  315  may include an annulus pressure port  345  therein, wherein the annulus pressure port  345  may be configured to couple a pressure source outside of the housing  315  proximate a stepped up area A C  of the pressure compensation piston  305 . The annulus pressure port  345  may allow fluid flow between the pressure source radially outside of the housing  315  and the cavity  310 , and thus add to the left to right (e.g., downward in the illustrated embodiment) force upon the pressure compensation piston  305 . 
     In some embodiments, there may be one or more radial bearings  350  positioned within the cavity  310 , wherein the radial bearings  350  may be configured to assist the rotation of the rotatable shaft  320  relative to the housing  315 . In certain embodiments, there may be a thrust bearing  355  positioned between the radial bearings  350 , wherein the thrust bearing  355 , in combination with the radial bearings  350  may be configured to prevent rotatable shaft  320  from sliding longitudinally with respect to the housing  315 . In some embodiments, the pressure compensation piston  305  may be positioned uphole of one or both of the radial bearings  350  and the thrust bearing  355 . In other embodiments, the pressure compensation piston  305  may be placed in other locations within the cavity  310 . 
     When the bore pressure from the rotatable shaft  320  and annulus pressure from the annulus pressure port  345  act on the pressure compensation piston  305 , the pressure compensation piston  305 , in some embodiments, slides longitudinally (left to right) with respect to the housing  315 , thereby transferring the pressure exerted on the first dynamic rotary seal  325 , reducing the bore pressure and the annulus pressure acting on the first dynamic rotary seal  325  and resulting in an intermediate pressure amount between the bore pressure and the annulus pressure. The foregoing pressure compensation is shown in the sample calculations in Table 1 herein. 
     The pressure compensation piston  305  operates under the law of pressure (P) equals force (F) over area (A), P=F/A. Referring to Table 1 disclosed herein in conjunction with  FIG. 2  and  FIG. 3 , there is shown an example of calculations illustrating the change of pressure across one embodiment of a rotary seal assembly such as rotary seal assembly  300  including one embodiment of the pressure compensation piston  305 . The stepped piston comprising the pressure compensation piston  305  may have areas A A , A B , and A C  which may correspond with the diameters D 0 , D 1 , and D 2  shown in  FIG. 2  for stepped piston  205 . Embodiments of the pressure compensation piston  305  use the different areas of the piston A A , A B , and A C  to apply a force to a larger area and thereby compensate for higher pressures. 
     As shown in Table 1, Force 1=Area A (A A )×Pressure 1. Pressure 1, in this embodiment, may be bore pressure. Force 1 may represent the force exerted on the radial surface of the opening within the pressure compensation piston  305  at Area A (A A ). Force 2=Area B×Pressure 2. Pressure 2, in this embodiment is may be annulus pressure, as it might be provided by the annulus pressure port  345 . Force 2 may represent the force exerted on at least a portion of the radially exterior surface of the second diameter (D 2 ) portion of the pressure compensation piston  305 . Force 3=Force 1+Force 2. As shown in Table 1, the pressure at Area 1 (A A ) is higher than the pressure at Area 3 (A C ). In this example, as the pressure at the piston may then be calculated. Knowing the bore pressure, annulus pressure, and pressure at the piston, the pressure differential across those three features can be calculate. Thus, whereas the pressure differential across the rotary seal  325  would have been 8.28 MPa without the stepped pressure compensation piston  305 , the inclusion of the stepped pressure compensation piston  305  reduces the pressure differential across the rotary seal  325  to 3.10 MPa. As such, the pressure exerted on the dynamic rotary seal  315  may be reduced, which may lessen the probability of the rotary seal  315  failing and reduce the amount of fluid leaking from the rotary seal. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Example of pressure calculations with  
               
               
                 one pressure compensation piston 
               
            
           
           
               
               
               
            
               
                   
                   
                 Piston 1 
               
               
                   
                   
               
            
           
           
               
               
               
            
               
                   
                 Bore Pressure (MPa) 
                 172.41 
               
               
                   
                 Annulus Pressure (MPa) 
                 164.14 
               
               
                   
                 Tool Pressure Drop (MPa) 
                 8.28 
               
               
                   
                 Diameter A (D 0 )(cm) 
                 2.54 
               
               
                   
                 Diameter B (D 1 )(cm) 
                 5.08 
               
               
                   
                 Diameter C (D 2 )(cm) 
                 7.62 
               
               
                   
                 Area A (A A )(cm 3 ) 
                 15.19 
               
               
                   
                 Area B (A B )(cm 3 ) 
                 25.32 
               
               
                   
                 Area C (A C )(cm 3 ) 
                 40.52 
               
               
                   
                 Force 1 (Bore Pressure) 
                 2620 
               
               
                   
                 Force 2 (Annulus Pressure) 
                 4156 
               
               
                   
                 Force 3 (Force 1 + Force 2) 
                 6776 
               
               
                   
                 Pressure at Piston (MPa) 
                 167.24 
               
               
                   
                 Pres Diff Bore-Piston (MPa) 
                 5.17 
               
               
                   
                 Pres Diff Bore-Annulus (MPa) 
                 8.28 
               
               
                   
                 Pres Diff Piston-Annulus (MPa) 
                 3.10 
               
               
                   
                   
               
            
           
         
       
     
     Referring to  FIG. 4 , depicted is another embodiment of a rotary seal assembly  400  according to principles of the disclosure. The rotary seal assembly  400  is similar in many respects to the rotary seal assembly  300  of  FIG. 3 . Accordingly, like reference numbers have been used to reference similar, if not identical, features. The rotary seal assembly  400  differs, for the most part, from the rotary seal assembly  300 , in that the rotary seal assembly  400  includes a second pressure compensation piston  460  positioned within the cavity  310  between the housing  315  and the rotatable shaft  320 . The second pressure compensation piston  405  may be a stepped piston similar to pressure compensation piston  305  and may be configured to slide longitudinally with respect to the housing  315 . In this embodiment, the second pressure compensation piston  405  may be positioned uphole of the pressure compensation piston  305 . At least a first and second linear dynamic seal  430  and  435  may similarly be positioned between the second pressure compensation piston  405  and the housing  315 . 
     In some embodiments, there may be a third dynamic rotary seal  425  positioned along a radial surface of the opening of the second pressure compensation piston  405  for sealing the second pressure compensation piston  405  relative to the rotatable shaft  320 . In some embodiments, the housing  315  may include a second annulus pressure port  445  therein, wherein the second annulus pressure port  445  may be configured to couple a pressure source outside of the housing  315  proximate to a stepped up area A 2  of the second pressure compensation piston  405 . 
     Table 2 included herein provides an example of sample calculations showing pressure and force calculations for the rotary seal assembly  400  including a second pressure compensation piston  405 . Referring to the column in Table 2 showing the combined pressures with Piston 1+Piston 2, which is the combination of the pressure compensation piston  305  and the second pressure compensation piston  405 . Table 2 illustrates how adding one or more additional pressure compensation pistons may provide further reduction of pressure differential across the first dynamic rotary seal  325  and the third rotary seal  425 . Thus, whereas the pressure differential across the rotary seal  325  would have been 8.28 MPa without the stepped pressure compensation piston  305  and stepped pressure compensation piston  405 , the inclusion of the first stepped pressure compensation piston  305  and second pressure compensation piston  405  reduces the pressure differential across the third rotary seal  425  to 3.10 MPa and first rotary seal  325  to 1.16 MPa. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Example of pressure calculations with a first  
               
               
                 and second pressure compensation piston: 
               
            
           
           
               
               
               
               
            
               
                   
                   
                   
                 Piston 1 +  
               
               
                   
                   
                 Piston 1 
                 Piston 2 
               
               
                   
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Bore Pressure (MPa) 
                 172.41 
                 167.24 
               
               
                   
                 Annulus Pressure (MPa) 
                 164.14 
                 164.14 
               
               
                   
                 Tool Pressure Drop (MPa) 
                 8.28 
                 3.10 
               
               
                   
                 Diameter A (D 0 )(cm) 
                 2.54 
                 2.54 
               
               
                   
                 Diameter B (D 1 )(cm) 
                 5.08 
                 5.08 
               
               
                   
                 Diameter C (D 2 )(cm) 
                 7.62 
                 7.62 
               
               
                   
                 Area A (A A )(cm 3 ) 
                 15.19 
                 15.19 
               
               
                   
                 Area B (A B )(cm 3 ) 
                 25.32 
                 25.32 
               
               
                   
                 Area C (A C )(cm 3 ) 
                 40.52 
                 40.52 
               
               
                   
                 Force 1 (Bore Pressure) 
                 2620 
                 2541 
               
               
                   
                 Force 2 (Annulus Pressure) 
                 4156 
                 4156 
               
               
                   
                 Force 3 (F1 + F2) 
                 6776 
                 6697 
               
               
                   
                 Pressure at Piston (MPa) 
                 167.24 
                 165.30 
               
               
                   
                 Pres Diff Bore-Piston (MPa) 
                 5.17 
                 1.94 
               
               
                   
                 Pres Diff Bore-Annulus (MPa) 
                 8.28 
                 3.10 
               
               
                   
                 Pres Diff Piston-Annulus (MPa) 
                 3.10 
                 1.16 
               
               
                   
                   
               
            
           
         
       
     
     Aspects disclosed herein include: 
     A. Provided is a pressure compensation piston for use with a rotary seal assembly, the pressure compensation piston including: 1) a stepped piston having an opening extending there through for positioning the stepped piston about a rotatable shaft of a rotary seal assembly; and 2) a rotary seal positioned along a radial surface of the opening for sealing the stepped piston relative to the rotatable shaft. 
     B. A rotary seal assembly, the rotary seal assembly including: 1) a housing; 2) a rotatable shaft positioned in a longitudinal opening in the housing, the housing and rotatable shaft forming a cavity there between; and 3) a pressure compensation piston positioned in the cavity, the pressure compensation piston including: a) a stepped piston having an opening extending there through for positioning the stepped piston about the rotatable shaft; and b) a rotary seal positioned along a radial surface of the opening for sealing the stepped piston relative to the rotatable shaft. 
     C. A well system, the well system including: 1) a wellbore located within a subterranean formation; 2) a rotary seal assembly positioned in the wellbore via a conveyance, the rotary seal assembly including: a) a housing; b) a rotatable shaft positioned in a longitudinal opening in the housing, the housing and rotatable shaft forming a cavity there between; and c) a pressure compensation piston positioned in the cavity, the pressure compensation piston including: i) a stepped piston having an opening extending there through for positioning the stepped piston about the rotatable shaft; and ii) a rotary seal positioned along a radial surface of the opening for sealing the stepped piston relative to the rotatable shaft. 
     Aspects A, B, and C may have one or more of the following additional elements in combination: Element 1: wherein the opening includes a diameter (D 0 ) and a circumferential profile extending radially outward into the stepped piston, the rotary seal positioned within the circumferential profile. Element 2: wherein the stepped piston includes a first diameter (D 1 ) portion and a second greater diameter (D 2 ) portion, and further wherein the circumferential profile is located in the first diameter (D 1 ) portion. Element 3: further including one or more linear dynamic seals for sealing the stepped piston relative to a housing surrounding the pressure compensation piston. Element 4: wherein a first linear dynamic seal is positioned at least partially within a radially exterior surface of the first diameter (D 1 ) portion to seal the first diameter (D 1 ) portion relative to the housing, and further wherein a second linear dynamic seal is positioned at least partially within a radially exterior surface of the second diameter (D 2 ) portion to seal the second diameter (D 2 ) portion relative to the housing. Element 5: further comprising an annulus pressure port in the housing, the annulus pressure port configured to couple a pressure source outside of the housing to a stepped up area of the stepped piston. Element 6: wherein the opening includes a diameter (D 0 ) and a circumferential profile extending radially outward into the stepped piston, the rotary seal positioned within the circumferential profile. Element 7: wherein the stepped piston includes a first diameter (D 1 ) portion and a second greater diameter (D 2 ) portion, and further wherein the circumferential profile is located in the first diameter (D 1 ) portion. Element 8: further comprising one or more linear dynamic seals for sealing the stepped piston relative to a housing surrounding the pressure compensation piston. Element 9: wherein a first linear dynamic seal is positioned at least partially within a radially exterior surface of the first diameter (D 1 ) portion to seal the first diameter (D 1 ) portion relative to the housing, and further wherein a second linear dynamic seal is positioned at least partially within a radially exterior surface of the second diameter (D 2 ) portion to seal the second diameter (D 2 ) portion relative to the housing. Element 10: wherein the rotary seal is a first rotary seal, and further including a second rotary seal positioned proximate and between an outer radial surface of the rotatable shaft and an inner radial surface of the longitudinal opening for sealing the rotatable shaft relative to the housing. Element 11: wherein the circumferential profile is a first circumferential profile, and further including a second circumferential profile extending radially inward into the rotatable piston, the second rotary seal positioned within the second circumferential profile. Element 12: wherein the pressure compensation piston is a first pressure compensation piston positioned in the cavity, and further including a second pressure compensation piston positioned in the cavity, the second pressure compensation piston including a second stepped piston having a second opening extending there through for positioning the second stepped piston about the rotatable shaft, and a third rotary seal positioned along a radial surface of the second opening for sealing the second stepped piston relative to the rotatable shaft. Element 13: further including a radial bearing positioned within the cavity. Element 14: wherein the pressure compensation piston is positioned uphole in the cavity relative to the radial bearing. Element 15: further including a thrust bearing positioned within the cavity. Element 16: further comprising a second radial bearing positioned within the cavity and downhole of the thrust bearing. Element 17: wherein the pressure compensation piston and the housing are rotationally fixed relative to one another and are configured to rotate relative to the rotatable shaft. 
     Those skilled in the art to which this application relates will appreciate that other and further additions, deletions, substitutions and modifications may be made to the described embodiments.