Patent Publication Number: US-11377924-B2

Title: Method and system for boosting sealing elements of downhole barriers

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a national stage under 35 USC 371 of International Application No. PCT/20/35504 filed on 1 Jun. 2020, which claims priority to U.S. Application No. 62/859,977 filed on 11 Jun. 2019. The entire disclosures of these prior applications are incorporated herein by this reference. 
    
    
     TECHNICAL FIELD 
     This disclosure relates generally to equipment utilized and operations performed in conjunction with a subterranean well and, in an example described below, more particularly provides a method and system for boosting sealing elements of downhole barriers. 
     BACKGROUND 
     A typical plug, packer or other downhole barrier for use in a subterranean well includes bi-directional slips which anchor the downhole barrier to well casing, tubing or other surface external to the barrier, prior to pack-off of a seal element to form a pressure seal. The pack-off force is applied to the seal element by compressing it between gage rings of the downhole barrier. 
     It is important for the seal element to remain sealed against the external surface, until the downhole barrier is intentionally unset, drilled through, or otherwise intentionally relieved of its sealing capability. If the seal element leaks prior to being intentionally relieved of its sealing capability, well operations may be severely compromised. 
     It will be appreciated, therefore, that improvements are continually needed in the art of constructing and utilizing downhole barriers. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a representative partially cross-sectional view of an example of a well system and associated method which can embody principles of this disclosure. 
         FIGS. 2A-G  are representative cross-sectional views of successive axial sections of an example of a downhole barrier which can embody the principles of this disclosure, the downhole barrier being depicted in a run-in configuration. 
         FIGS. 3A-G  are representative cross-sectional views of successive axial sections of the downhole barrier in a set configuration. 
         FIG. 4  is a representative cross-sectional view of a boost system of the downhole barrier. 
         FIG. 5  is a representative cross-sectional view of the boost system, in which pressures applied to chambers in a boost housing of the boost system counteract each other. 
         FIG. 6  is a representative cross-sectional view of the boost system, in which a lock ring permits the boost housing to displace upward relative to an upper wedge of the downhole barrier. 
         FIG. 7  is a representative cross-sectional view of the boost system, in which a lock ring permits a housing to displace downward relative to a lower wedge of the downhole barrier. 
         FIGS. 8A  &amp; B are representative cross-sectional views of upper and lower sections of the downhole barrier in an equalized configuration. 
         FIGS. 9A-G  are representative cross-sectional views of successive axial sections of the downhole barrier in an unset configuration. 
     
    
    
     DETAILED DESCRIPTION 
     Representatively illustrated in  FIG. 1  is a system  10  for use with a subterranean well, and an associated method, which can embody principles of this disclosure. However, it should be clearly understood that the system  10  and method are merely one example of an application of the principles of this disclosure in practice, and a wide variety of other examples are possible. Therefore, the scope of this disclosure is not limited at all to the details of the system  10  and method described herein and/or depicted in the drawings. 
     In the  FIG. 1  example, a downhole barrier  12  is positioned in a wellbore  14  and is set therein. When set, the barrier  12  isolates an upper section  16  of the wellbore  14  from a lower section  18  of the wellbore. The barrier  12  blocks and prevents flow through an annulus  20  formed radially between a tubular string  22  and the wellbore  14 . 
     The barrier  12  can be set in casing  24  that lines the wellbore  14 , or the barrier could be set in another tubular string. In some examples, the barrier  12  may be set in an uncased or open hole section of the wellbore  14 . 
     The downhole barrier  12  depicted in  FIG. 1  is of the type known to those skilled in the art as a packer. In other examples, the downhole barrier  12  could be in the form of a bridge plug, a liner hanger or another type of downhole barrier. The scope of this disclosure is not limited to use of any particular type of downhole barrier. 
     Bridge plugs and packers are examples of downhole barriers that can be set at a predetermined depth anywhere within a wellbore, tubing or casing to facilitate a wide range of well support operations. Once installed, for example, they may be used to isolate the upper wellbore section  16  from production, or the lower wellbore section  18  from treatments conducted uphole. 
     For some conventional bridge plugs or packers, the seal element thereof is packed off (compressed so that it seals against an external surface) with an initial pack-off force. A distance between gage rings remains fixed after pack-off and while the seal element contacts the external surface. During well operations, as a differential pressure applied across the seal element changes (such as, due to variations in formation pressure and temperature in the wellbore), the element volume can change from its initial pack-off state. 
     With no additional pack-off force, these volume changes may reduce the seal element&#39;s ability to maintain its sealing engagement with the external surface. Therefore, when a subsequent differential pressure is applied, or when the direction of pressure is changed, these seal elements can lose their initial sealing capability and leak. 
     In some designs, a mandrel on which the seal element is carried is allowed to move axially (up or down) relative to the seal element. This allows a total area of the mandrel to be acted on by pressure in the wellbore above the barrier, resulting in a downwardly directed boost force applied to the seal element. This boost force can be excessive. 
     During well operations, as differential pressure is applied across the seal element at elevated temperature, the seal element may extrude past the gage rings and leak. Bridge plugs and packers with such boost systems tend to have different differential pressure ratings, depending on whether the differential pressure is applied from above or below. This situation does not maximize the sealing capability of the seal element. 
     Described below is a boost system (an apparatus to maintain seal element compression) in which the seal element does not disengage from the surrounding wellbore, casing or other tubular when exposed to fluctuating operational conditions, but instead maintains its sealing capability. This is a boost system that will adapt to a changing wellbore environment, and that supplies additional pack-off force to the seal element in response to an increase in pressure differential from above or below. 
     This system provides for control of boost areas subject to differential pressures from above and below. Therefore, any downhole barrier with this boost system can have a same pressure differential rating for differential pressures from above and below, and with enhanced sealing capability. However, it is not necessary in keeping with the principles of this disclosure for a downhole barrier to have an exact same pressure differential rating for differential pressures from above and below. 
     In one example, this boost system includes (see  FIG. 4 ) a boost housing  32  slidingly arranged on a piston  34  formed on the mandrel  38 , with a unidirectional body lock ring  36  to trap a boost force in a seal element  28 . A difference in area between an inner seal bore (area B) of the housing  32  and a seal diameter (area C) on the mandrel  38  downhole of the piston  34  is a “downhole” boost area (B−C) that can be used to apply a compressive force to the seal element  28  due to a pressure differential from downhole to uphole across the barrier  12  (e.g., from the wellbore section  18  to the wellbore section  16  in the  FIG. 1  system  10 ). 
     This method can be used to optimize boost areas (and resulting compressive forces) for enhanced sealing capability. The boost areas from uphole and downhole directions can be equal or different. As used herein, the downhole direction is toward a distal end of the wellbore  14  (farthest from surface along the wellbore) and the uphole direction is toward a proximal end of the wellbore (at the surface). 
     If the downhole boost area (B−C) is equal to the uphole boost area (A−B+C), then the outer area A of the mandrel  38  above the piston  34  is equal to twice the difference between the inner area B of the seal bore of the boost housing  32  and the outer area C of the mandrel below the piston (A=2×(B−C)). However, in some examples the downhole boost area may not be equal to the uphole boost area. 
     One example described herein comprises boost and counter-boost piston areas. A difference between the boost and counter-boost piston areas equals a resulting net boost area. 
     Pressure applied to an inner mandrel  38  is used in the  FIG. 4  example to apply a compressive force to the seal element  28  due to a pressure differential from uphole to downhole across the barrier  12  (e.g., from the wellbore section  16  to the wellbore section  18  in the  FIG. 1  system  10 ). The difference in area between the mandrel  38  outer diameter (area A) on which the seal element  28  is seated and the boost area described above (B−C) equals the net boost area (A−B+C) that can be used to apply a compressive force to the seal element  28  due to a pressure differential from uphole to downhole across the barrier  12 . A housing  40  that is connected to the mandrel  38  (see  FIG. 7 ) has a unidirectional body lock ring  42  to trap the boost force (resulting from the pressure applied to the net boost area) in the seal element  28 . 
     In this example, the piston  34  is used to cancel or balance some of the downwardly directed boost force due to pressure applied to the mandrel  38 . This concept may be used with any type of downhole barrier with a “boosting” mandrel. 
     When a pressure differential is applied from above the seal element  28 , the mandrel  38  will be biased to displace toward the seal element. The pressure differential multiplied by the net downward boost area will produce a compressive boost force on the seal element  28 . This additional compressive force helps maintain the sealing capability of the seal element  28 . The body lock ring  42  (see  FIG. 7 ) is used to trap the compressive boost force in the seal element  28 . 
     Alternatively, when a pressure differential is applied from downhole to uphole across the seal element  28 , the housing  32  and piston  34  will be biased to displace toward the seal element to exert a compressive force on the seal element. The pressure differential multiplied by the net boost area will produce a compressive force on the seal element  28 . This additional compressive force helps maintain the sealing capability of the seal element  28 . The body lock ring  36  is used to trap the boost force in the seal element  28 . 
     When the downhole barrier  12  is unset, all the compressive forces are removed from the seal element  28  and it is allowed to relax for retrieval. Using the principles described herein, the seal element  28  can seal against relatively large pressure differentials and, when unset, a maximum outer diameter OD (see  FIG. 2E ) of the downhole barrier  12  can be at its original run-in maximum outer diameter. 
     Referring to  FIGS. 2A-G , cross-sectional views of successive axial sections of a more detailed example of the downhole barrier  12  are representatively illustrated. In  FIGS. 2A-G , the downhole barrier  12  is of the type known to those skilled in the art as a bridge plug. When used in the  FIG. 1  system  10 , the downhole barrier  12  would be used to completely isolate the wellbore sections  16 ,  18  from each other. The downhole barrier  12  may be used in other systems and methods in keeping with the principles of this disclosure. 
     In the run-in configuration of  FIGS. 2A-G , the downhole barrier  12  is not set. Slips  26  and the seal element  28  are inwardly retracted, so that the downhole barrier  12  can be conveyed through the wellbore  14  to a desired location for setting the barrier. 
     In this example, the seal element  28  comprises several components  28   a - c , along with support and backup devices  28   d - g . Gage rings  30   a,b  straddle the seal element  28  and are displaceable axially relative to the mandrel  38 . 
     When an axial distance between the gage rings  30   a,b  decreases, compressive force in the seal element  28  increases and the seal element extends radially outward. Conversely, when the axial distance between the gage rings  30   a,b  increases, the compressive force in the seal element decreases and the seal element retracts radially inward. 
     The upper gage ring  30   a  is initially releasably secured via shear screws  44  against axial displacement relative to the mandrel  38 . Thus, when the mandrel  38  is biased upward or downward, the upper gage ring  30   a  is similarly biased, and the upper gage ring displaces axially with the mandrel  38 . 
     At its upper end, the mandrel  38  is connected to a ported housing  46  and an upper sleeve  48 . Reciprocably received in the upper sleeve  48  is a connector  50  of the type known to those skilled in the art as a “fishing” neck. The connector  50  may be used to connect the downhole barrier  12  to a setting tool. 
     The connector  50  is also connected to an inner sleeve  52  that extends axially through most of the downhole barrier  12  within the mandrel  38 . The connector  50  may be used to displace the inner sleeve  52  axially relative to the mandrel  38 . 
     The lower gage ring  30   b  is connected to the boost housing  32 . Thus, when the housing  32  is biased upward or downward, the lower gage ring  30   b  is similarly biased, and the lower gage ring displaces axially with the housing  32 . 
     The boost housing  32  is connected to another housing  54  having a surface  54   a  grippingly engaged by the lock ring  36 . The lock ring  36  permits downward displacement of an upper wedge  56   a  relative to the housings  32 ,  54  but prevents upward displacement of the upper wedge  56   a  relative to the housings  32 ,  54 . 
     The upper wedge  56   a  underlies an upper section of the slips  26 . A similar lower wedge  56   b  underlies a lower section of the slips  26 . The upper and lower wedges  56   a,b  have a series of frusto-conical ramps, inclines or wedges formed thereon. When an axial distance between the wedges  56   a,b  is decreased, the slips  26  are thereby displaced radially outward. When the axial distance between the wedges  56   a,b  is increased, the slips  26  are thereby displaced radially inward. 
     The lower wedge  56   b  is connected to the housing  40  via the lock ring  42 . The lower wedge  56   b  also axially abuts the housing  40 , and so compressive force can be transmitted between the lower wedge  56   b  and the housing  40 . The lock ring  42  permits upward displacement of the lower wedge  56   b  relative to the housing  40 , but prevents downward displacement of the lower wedge relative to the housing  40 . 
     The housing  40  is connected to the mandrel  38  via a releasable connector  58 . The releasable connector  58  has threaded lugs  60  that are propped radially outward by a sleeve  62  into engagement with internal threads in the housing  40 . 
     The sleeve  62  is connected to the inner sleeve  52  via a lock ring  64 . The lock ring  64  permits downward displacement of the inner sleeve  52  relative to the sleeve  62 , but prevents upward displacement of the inner sleeve  52  relative to the sleeve  62 . 
     Near a lower end of the downhole barrier  12 , a valve sleeve  66  blocks flow through ports  68 . The valve sleeve  66  prevents fluid communication between an exterior of the downhole barrier  12  (e.g., corresponding to the lower wellbore section  18  in the  FIG. 1  system  10 ) and an internal flow passage  70  extending axially through most of the downhole barrier  12 . A bull plug  72  closes off a lower end of the flow passage  70  and the downhole barrier  12 . 
     Referring now to  FIGS. 3A-G , the downhole barrier  12  is representatively illustrated in a set configuration. Note that the seal element  28  is axially compressed and radially extended outward, so that it can sealingly engage an interior surface of a wellbore, a casing or another tubular. The slips  26  are outwardly extended, so that they can grippingly engage the interior surface of the wellbore, casing or other tubular and thereby prevent displacement of the downhole barrier  12  in the wellbore  14 . 
     To set the downhole barrier  12 , a setting tool  74  (see  FIG. 1 ) can be used to apply a downward force to an outer setting sleeve  76 , thereby shearing the shear screws  44  and displacing the outer setting sleeve downward relative to the mandrel  38 . The setting sleeve  76  is connected to the upper gage ring  30   a . Thus, downward displacement of the setting sleeve  76  relative to the mandrel  38  results in downward displacement of the upper gage ring  30   a , the seal element  28 , the lower gage ring  30   b , the housings  32 ,  54 , the upper wedge  56   a  and the slips  26  relative to the mandrel  38 . 
     The lower wedge  56   b  remains fixed relative to the mandrel  38  via the releasable connector  58  and the housing  40 . Thus, the axial distance between the upper and lower wedges  56   a,b  is reduced and the slips  26  are displaced outward to their set configuration. 
     The axial distance between the gage rings  30   a,b  is also reduced. The seal element  28  is axially compressed between the gage rings  30   a,b  and is deformed radially outward to its set configuration. 
     Referring additionally now to  FIG. 4 , the boost system of the downhole barrier  12  is representatively illustrated with the barrier in the set configuration. In this view it may be seen that fluid pressure in the flow passage  70  (and in the upper wellbore section  16  in the  FIG. 1  system  10 ) is communicated to a chamber  78  below the piston  34  via ports  80  formed radially through the piston. Another chamber  82  is above the piston  34  and is in communication with pressure external to the downhole barrier  12  below the seal element  28  (e.g., the lower wellbore section  18  in the  FIG. 1  system  10 ). 
     By carefully selecting the areas corresponding to the diameters A, B &amp; C, the additional pack-off force or compressive boost force applied to the seal element  28  due to a pressure differential from above to below or from below to above the downhole barrier  12  can be made equal if desired. In addition, excessive boost force due to a pressure differential from above to below applied to the mandrel  38  can be avoided. 
     Referring to  FIG. 5 , the manner in which the pressures applied to the chambers  78 ,  82  in the boost housing  32  counteract each other can be more clearly seen. Pressure applied to the lower chamber  78  and acting on a lower piston area of the piston  34  biases the mandrel  34  upward and the boost housing  32  downward. Pressure applied to the upper chamber  82  and acting on an upper piston area of the piston  34  biases the mandrel  34  downward and the boost housing  32  upward. 
     Referring to  FIG. 6 , the lock ring  36  permits the boost housing  32  to displace upward relative to the upper wedge  56   a . Thus, increased pressure differential from below applied to the upper chamber  82  will bias the boost housing  32  and lower gage ring  30   b  to displace upward to thereby increase the compressive force in the seal element  28 . The lock ring  36  will prevent any subsequent downward displacement of the boost housing  32  relative to the upper wedge  56   a.    
     Referring to  FIG. 7 , the lock ring  42  permits the housing  40  to displace downward relative to the lower wedge  56   b . Thus, increased pressure differential from above applied to the lower chamber  78  will bias the mandrel  38  and upper gage ring  30   a  to displace downward to thereby increase the compressive force in the seal element  28 . The lock ring  42  will prevent any subsequent upward displacement of the mandrel  38  and housing  40  relative to the lower wedge  56   b.    
     Referring to  FIGS. 8A  &amp; B, upper and lower ends of the downhole barrier  12  are representatively illustrated in an equalized configuration in preparation for unsetting the barrier. In this configuration, pressures above and below the downhole barrier  12  (e.g., in the upper and lower wellbore sections  16 ,  18 ) are equalized by placing them in fluid communication with each other, prior to unsetting the barrier. 
     As depicted in  FIG. 8A , the connector  50  and inner sleeve  52  are displaced downward relative to the upper sleeve  48  and ported housing  46 . The flow passage  70  is thereby placed in fluid communication with the exterior of the barrier  12  above the seal element  28  via ports  84  in the inner sleeve  52  and ports  86  in the ported housing  46 . 
     As depicted in  FIG. 8B , when the inner sleeve  52  is displaced downward, it engages and downwardly displaces the valve sleeve  66 . In this manner, the flow passage  70  is placed in fluid communication with the exterior of the barrier  12  below the seal element  28  via ports  88  in the inner sleeve  52  and the ports  68 . Thus, pressures above and below the barrier  12  are equalized in preparation for unsetting the barrier. 
     Referring to  FIGS. 9A-G , the downhole barrier  12  is representatively illustrated in an unset configuration. Note that the maximum OD of the barrier  12  is no greater in the unset configuration than it was in the original, run-in configuration of the barrier depicted in  FIGS. 2A-G . 
     The connector  50  is displaced upward, so that the mandrel  38  is no longer connected to the housing  40  via the releasable connector  58 . The sleeve  62  is displaced upward with the inner sleeve  52 , and the lugs  60  are no longer supported in engagement with the housing  40 . 
     The housing  40  and the lower wedge  56   b  are displaced downward, thereby increasing the axial distance between the upper and lower wedges  56   a,b  and allowing the slips  26  to inwardly retract. The axial distance between the upper and lower gage rings  30   a,b  is also increased, thereby relieving the compressive force in the seal element  28  and allowing it to retract radially inward. The barrier  12  can now be conveniently retrieved from the well. 
     It may now be fully appreciated that the above disclosure provides significant advancements to the art of constructing and utilizing downhole barriers for use in subterranean wells. In examples described above, the downhole barrier  12  includes boost areas for applying compressive boost forces to the seal element  28  in response to pressure differentials applied in uphole and downhole directions. 
     The above disclosure provides to the art a downhole barrier  12  for use in a subterranean well. In one example, the downhole barrier  12  can include a boost housing  32  disposed axially between a slip  26  and a seal element  28 , a mandrel  38  extending axially through the boost housing  32  and the seal element  28 , and a piston  34  fixed to the mandrel  38 , the piston  34  separating first and second fluid chambers  78 ,  82  in the boost housing  32 . The first fluid chamber  78  is positioned axially between the slip  26  and the second fluid chamber  82 . The first fluid chamber  78  is in fluid communication with an interior flow passage  70  of the mandrel  38 , and the second fluid chamber  82  is in fluid communication with an exterior of the downhole barrier  12 . 
     An outer area A of the mandrel  38  in the second fluid chamber  82  may be equal to twice a difference between an inner area B of the boost housing  32  and an outer area C of the mandrel  38  in the first fluid chamber  78 . 
     The downhole barrier  12  may include a wedge  56   a  configured to outwardly extend the slip  26 . A lock ring  36  may permit axial displacement of the boost housing  32  away from the wedge  56   a  and prevent axial displacement of the boost housing  32  toward the wedge  56   a.    
     The downhole barrier  12  may include a wedge  56   b  configured to outwardly extend the slip  26 . A lock ring  42  may permit displacement of the mandrel  38  in a first axial direction relative to the wedge  56   b  and prevent displacement of the mandrel  38  in a second axial direction relative to the wedge  56   b , the second axial direction being opposite to the first axial direction. 
     In a set configuration of the downhole barrier  12 , a first pressure differential applied in a first axial direction (e.g., from uphole to downhole) across the seal element  28  may cause a first compressive force to be applied to the seal element  28 , and a second pressure differential applied in a second axial direction (e.g., from downhole to uphole) across the seal element  28  may cause a second compressive force to be applied to the seal element  28 . The first and second pressure differentials may be equal, the first and second compressive forces may be equal, and the second axial direction may be opposite to the first axial direction. 
     The boost housing  32  may be rigidly connected to a gage ring  30   b . The gage ring  30   b  may be configured to transmit a compressive force from the boost housing  32  to the seal element  28 . 
     The first and second fluid chambers  78 ,  82  may have a same outer diameter (e.g., corresponding to area B). The first and second fluid chambers  78 ,  82  may have different inner diameters (e.g., corresponding to areas C &amp; A). 
     The interior flow passage  70  may extend axially through the mandrel  38 . 
     The seal element  28  may be configured to extend radially outward in response to a compressive force applied to the seal element  28 . 
     Also provided to the art by the above disclosure is a system  10  for use with a subterranean well. In one example, the system  10  can include a downhole barrier  12  set in a wellbore  14  of the well. In this example, the downhole barrier  12  includes a boost housing  32  disposed axially between a slip  26  and a seal element  28 , a mandrel  38  extending axially through the boost housing  32  and the seal element  28 , and a piston  34  fixed to the mandrel  38 . The piston  34  separates first and second fluid chambers  78 ,  82  in the boost housing  32 . An outer area A of the mandrel  38  in the second fluid chamber  82  is equal to twice a difference between an inner area B of the boost housing  32  and an outer area C of the mandrel  38  in the first fluid chamber  78 . 
     Although various examples have been described above, with each example having certain features, it should be understood that it is not necessary for a particular feature of one example to be used exclusively with that example. Instead, any of the features described above and/or depicted in the drawings can be combined with any of the examples, in addition to or in substitution for any of the other features of those examples. One example&#39;s features are not mutually exclusive to another example&#39;s features. Instead, the scope of this disclosure encompasses any combination of any of the features. 
     Although each example described above includes a certain combination of features, it should be understood that it is not necessary for all features of an example to be used. Instead, any of the features described above can be used, without any other particular feature or features also being used. 
     It should be understood that the various embodiments described herein may be utilized in various orientations, such as inclined, inverted, horizontal, vertical, etc., and in various configurations, without departing from the principles of this disclosure. The embodiments are described merely as examples of useful applications of the principles of the disclosure, which is not limited to any specific details of these embodiments. 
     In the above description of the representative examples, directional terms (such as “above,” “below,” “upper,” “lower,” etc.) are used for convenience in referring to the accompanying drawings. However, it should be clearly understood that the scope of this disclosure is not limited to any particular directions described herein. 
     The terms “including,” “includes,” “comprising,” “comprises,” and similar terms are used in a non-limiting sense in this specification. For example, if a system, method, apparatus, device, etc., is described as “including” a certain feature or element, the system, method, apparatus, device, etc., can include that feature or element, and can also include other features or elements. Similarly, the term “comprises” is considered to mean “comprises, but is not limited to.” 
     Of course, a person skilled in the art would, upon a careful consideration of the above description of representative embodiments of the disclosure, readily appreciate that many modifications, additions, substitutions, deletions, and other changes may be made to the specific embodiments, and such changes are contemplated by the principles of this disclosure. For example, structures disclosed as being separately formed can, in other examples, be integrally formed and vice versa. Accordingly, the foregoing detailed description is to be clearly understood as being given by way of illustration and example only, the spirit and scope of the invention being limited solely by the appended claims and their equivalents.