Patent Publication Number: US-2012038115-A1

Title: Anti-Extrusion Seal for High Temperature Applications

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable. 
     BACKGROUND 
     To form an oil or gas well, a bottom hole assembly (BHA), including components such as a motor, steering assembly, one or more drill collars, and a drill bit, is coupled to a length of drill pipe to form a drill string. Electronics for performing various downhole operations may be positioned in a chassis, which is, in turn, located within the drill string. The drill string is then inserted downhole, where drilling commences. During drilling, drilling fluid, or “drilling mud,” is circulated down through the drill string to lubricate and cool the drill bit as well as to provide a vehicle for removal of drill cuttings from the borehole. 
     Seals are positioned between the electronics chassis and adjacent drill string tubular(s) to prevent exposure of the electronics positioned in the chassis to drilling fluid. Like the remaining components of the drill string, the seals are exposed to high pressure loads resulting from the weight of the drilling fluid contained in the drill string and high temperature loads resulting from heat generated by contact between the drill bit and formation. High pressure and/or temperature loads may be problematic for the seals and potentially cause failure. 
     Some conventional seals are formed of compliant, thermally sensitive material that expands when exposed to high temperature and contracts when the surrounding temperature decreases. To ensure adequate sealing between the electronics chassis and the adjacent drill string tubular at relatively low temperatures, often the seal is preloaded, or compressed between the chassis and tubular to some pre-determined load. Later, when the seals are exposed to higher temperatures, the temperature sensitive material of the seals causes them to expand. As a result, the seals may extrude into annular spaces between the electronics chassis and adjacent tubular. High pressure loads acting on the compliant seal may promote extrusion of the seal into the annular spaces. Over time, repeated contraction and extrusion of the seals due to temperature changes and high-pressure loads may cause damage to the seals such that they fail and pressurized drilling fluid begins to leak between the electronics chassis and adjacent tubular, whereby the electronics positioned in the chassis are exposed to the drilling fluid. 
     SUMMARY OF DISCLOSED EMBODIMENTS 
     A system for sealing between a tubular and a chassis is disclosed. In some embodiments, the sealing system includes a sealing member and an outer ring. The sealing member is compressed between the chassis and the tubular. The sealing member has a temperature and comprises a resilient material that is expandable as the temperature increases and contractible as the temperature decreases. The outer ring is displaceable to close an annulus between an outer surface of the outer ring and the inner surface of the tubular by expansion of the sealing element, whereby the sealing member is prevented from extruding into the annulus. Further, the outer ring comprises a compliant material that is deformable under load from the sealing element as the sealing element expands. 
     In some embodiments, the sealing system includes a sealing member compressed between the chassis and the tubular and an outer ring disposed adjacent the sealing member and slideably engaging a radially extending surface of the chassis. The sealing member has a temperature and comprises a resilient material that is expandable as the temperature increases and contractible as the temperature decreases. The outer ring includes a substantially axially extending inner surface, an angled surface extending from the inner surface and engaging the sealing member, and a substantially axially extending outer surface disposed radially inward of an inner surface of the tubular. The sealing member is expandable to displace the outer ring radially outward, whereby an annulus between the outer surface of the outer ring and an inner surface of the tubular is closed and the sealing member is deflected by the angled surface of the outer ring away from the annulus. 
     In some embodiments, the sealing system includes a sealing member compressed between the chassis and the tubular, an inner ring disposed adjacent the sealing member and slideably engaging an axially extending surface of the chassis, and an outer ring disposed radially outward of the inner ring. The sealing member has a temperature and comprises a resilient material that is expandable as the temperature increases and contractible as the temperature decreases. The inner ring has an axially extending outer surface and an angled surface extending from the outer surface. The outer ring has a substantially axially extending inner surface, an angled surface extending from the inner surface and slideably engaging the angled surface of the inner ring, and a substantially axially extending outer surface disposed radially inward of an inner surface of the tubular. The sealing member is expandable to axially displace the inner ring, whereby the outer ring displaces radially outward to close an annulus between the outer surface of the outer ring and an inner surface of the tubular, whereby the sealing member is prevented from extruding into the annulus. 
     Thus, embodiments described herein comprise a combination of features and characteristics intended to address various shortcomings associated with certain prior devices. The various characteristics described above, as well as other features, will be readily apparent to those skilled in the art upon reading the following detailed description of the preferred embodiments, and by referring to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more detailed description of the disclosed embodiments, reference will now be made to the accompanying drawings, wherein: 
         FIG. 1  is a cross-sectional view of an embodiment of an anti-extrusion seal for high temperature applications in accordance with the principles disclosed herein; 
         FIG. 2  is a cross-sectional view of the anti-extrusion seal of  FIG. 1  after preloading; 
         FIG. 3  is a cross-sectional view of the anti-extrusion seal of  FIG. 1  after expansion due to exposure to higher temperatures; 
         FIG. 4  is a cross-sectional view of another embodiment of an anti-extrusion seal for high temperature applications in accordance with the principles disclosed herein; 
         FIG. 5  is a cross-sectional view of the anti-extrusion seal of  FIG. 4  after expansion due to exposure to higher temperatures; and 
         FIG. 6  is a cross-sectional view of the anti-extrusion seal of  FIG. 3  after further expansion due to exposure to higher temperatures. 
     
    
    
     DETAILED DESCRIPTION OF THE DISCLOSED EMBODIMENTS 
     Referring now to  FIG. 1 , an anti-extrusion seal  100  in accordance with the principles disclosed herein is depicted between a tubular  110  and an insert  105  disposed therein. In some embodiments, tubular  110  is a component of form a drill string for creating a well bore, such as but not limited to a drill collar, and insert  105  is a chassis within which electronics (not shown) for downhole measurements are positioned. Seal  100  is seated in a groove  115  disposed in the outer surface  120  of insert  105  and, when preloaded as will be described, provides a barrier to fluid flow into an annular space  165  between insert  105  and tubular  110  to protect the electronics positioned in insert  105 . 
     Seal  100  includes a sealing member  125  positioned between a resilient ring  130  and an inner preload ring  135 , an angular ring  140  disposed radially outward of resilient ring  130 , and an outer preload ring  145  abutting inner preload ring  135 . Sealing member  125  is compliant or flexible, and in some embodiments, comprises elastomeric material. Thus, sealing member  125  deforms in response to pressure loads, such as pressure loads from drilling fluid passing through tubular  110 . Further, sealing member  125  may be responsive to temperature change. As such, sealing member  125  may expand when exposed to temperatures exceeding the ambient temperature, and contract again when exposed to lower temperatures. 
     Moreover, sealing member  125  has a diameter  167 , or other equivalent dimension, which exceeds the radial clearance between an outer surface  160  of insert  105  and an inner surface  180  of tubular  110 . Consequently, sealing member  125  must be compressed to between insert  105  and tubular  110  when installed, as shown, thereby preloading seal  100  to a degree. Compressing sealing member  125  in this manner preloads seal  100  to a degree. Inner preload ring  135  and outer preload ring  145  enable further preloading of sealing member  125 , as will be described. In some embodiments, outer preload ring  145  is a Belleville washer or a wave spring. 
     Preloading of sealing member  125  occurs at ambient temperature, when sealing member  125  assumes its natural state in the absence of thermal expansion. Preloading of sealing member  125  involves compressing sealing member  125  sufficiently within groove  115  to cause sealing member  125  to engage both inner surface  180  of tubular  110  and axially extending surface  160  of insert  105 . Once sealing member  125  engages surfaces  160 ,  180 , sealing member  125  forms a barrier which prevents drilling fluid that may enter groove  115  through the annular space  195  between tubular  110  and inner preload ring  140 /outer preload ring  145  from bypassing sealing member  125  and entering annular space  165  between insert  105  and tubular  110 . 
     When seal  100  is subsequently exposed to increased temperatures, sealing member  125  expands, thereby increasing its ability to prevent drilling fluid from entering annular space  165 . When temperatures surrounding sealing member  125  later decrease, sealing member  125  contracts. However, because seal  100  was preloaded when sealing member  125  was is in its natural, unexpanded state, sealing member  125  remains in contact with surfaces  160 ,  180  and thus continues to provide a barrier to fluid flow into annular space  165  even in the absence of thermal loads from, for example, heat generated by drilling. 
     Resilient ring  130  and angular ring  140  are both made of compliant material. Hence, these components  130 ,  140  are deformable under contact loads from sealing member  125  and pressure loads from drilling fluid entering groove  115 . Further, when assembled as shown, resilient ring  130  and angular ring  140  are interfered, meaning they overlap, as indicated by dotted line  150 , which represents the radially outer surface of ring  130 . As shown, resilient ring  130  and angular ring  140  are interfered, or overlap, by a distance or interference  185 . Groove  115  of insert  105  is bounded by axially and radially extending surfaces  160 ,  155 , respectively, of insert  105 . Angular ring  140  is radially translatable over radially extending surface  155  of insert  105  relative to resilient ring  130 . Thus, interference  185  between resilient ring  130  and angular ring  140  increases as angular ring  140  translates radially inward over surface  155  further compressing resilient ring  130  against surfaces  155 ,  160  of insert  105 , and decreases as angular ring  140  translates radially outward over surface  155 . The dimensions of resilient ring  130  and angular ring  140  are selected such that these components  130 ,  140  remain interfered to a degree (meaning interference  185  is greater than zero) once installed between insert  105  and tubular  110 . As such, resilient ring  130  and angular ring  140  do not separate, thereby preventing an annular space from opening between these components  130 ,  140  that may provide an extrusion path for sealing member  125 . 
     Angular ring  140  has an angled surface  170  proximate sealing member  125 . As previously described, sealing member  125  expands when exposed to temperatures higher than ambient. When sealing member  125  expands against angled surface  170  of ring  140 , sealing member  125  deforms, due to its compliant nature, and is forced away from annular space  165  due to the angular nature of surface  170 . At the same time, angular ring  140  displaces radially outward over surface  155  of insert  105  under force from expanding sealing member  125 . As angular ring  140  displaces radially outward, an annular gap  175  between angular ring  140  and an inner surface  180  of tubular  110  decreases or closes. When sealing member  125  expands sufficiently to compress angular ring  140  against inner surface  180 , gap  175  is closed, and angular ring  140  forms a barrier that prevents sealing member  125  and any drilling fluid in groove  115  from entering annular space  165 . Thus, angular ring  140  prevents sealing member  125  from extruding into annular space  165 . 
     Outer preload ring  145  and, in some embodiments, inner preload ring  135 , allow for some thermal expansion of sealing member  125 . This combined with the compliant nature of angular ring  140  and resilient ring  130  permits limited expansion of sealing member  125 . By allowing sealing member  125  some room to expand, sealing member  125  is prevented from being compressed or squeezed during expansion to point where sealing member  125  becomes damaged and loses it resiliency. 
     As previously described, tubular  110  may form a portion of a drill string for creating a well bore and electronics (not shown) disposed within insert  105 , and protected by seal  100 , may perform downhole measurements. During assembly of the drill string, seal  100  is first assembled within groove  115  between insert  105  and tubular  110  prior to run-in of the drill string, including tubular  110 , into the borehole. To assemble seal  100 , resilient ring  130  is disposed within groove  115  abutting surfaces  155 ,  160 , as shown in  FIG. 1 . Next, angular ring  140  is positioned radially outward of and in interference with resilient ring  130 . Sealing member  125  is then positioned within groove  115  abutting first and angular rings  130 ,  140 , respectively. Inner preload ring  135  is next positioned about insert  105  against sealing member  125 . To complete assembly of seal  100 , outer preload ring  145  is then disposed over inner preload ring  135 . Insert  105  with seal  100  assembled thereto is then inserted within tubular  110 , as shown. 
     Inserting insert  105  within tubular  110  preloads sealing member  125  to a degree because sealing member  125  must be squeezed or compressed to fit between insert  105  and tubular  110 . Next, seal  100  is further preloaded, as illustrated by  FIG. 2 . A pre-selected compressive force  190  is applied to outer preload ring  145 . In response, inner preload ring  135  translates along surface  160  of insert  105  to compress sealing member  125 . The compressive force applied is selected to ensure sealing member  125  remains engaged with both inner surface  180  of tubular  110  and axially extending surface  160  of insert  105  and provides a barrier preventing drilling fluid from entering annular space  165  between insert  105  and tubular  110 , even when sealing member  125  assumes its natural state in the absence of thermal expansion. After seal  100  is preloaded, tubular  110  with insert  105  positioned therein may then be lowered into the borehole as part of the drill string. 
     During drilling operation, drilling fluid is delivered through the drill string, including tubular  110 , to the drill bit. Due to its weight, the drilling fluid is highly pressurized and will pass through any exposed spaces between insert  105  and tubular  110 , such as the annular space  195  between inner surface  180  of tubular  110  and inner preload ring  140 /outer preload ring  145 . However, due to preloading of seal  100 , sealing member  125  prevents the drilling fluid from bypassing sealing member  125  and entering annular space  165  between insert  105  and tubular  110 . At the same time, the temperature of sealing member  125  may also begin to rise in response to heat generated by drilling or increased downhole temperatures. As a result, sealing member  125  expands against angled surface  170  of angular ring  140 , thereby displacing angular ring  140  along radially extending surface  155  of insert  105  and closing gap  175  between angular ring  140  and tubular  110 . 
     Referring to  FIG. 3 , continued expansion of sealing member  125  displaces angular ring  140  such that gap  175  is closed and angular ring  140  is compressed against inner surface  180  of tubular  110 . Once gap  175  is closed, angular ring  140  prevents extrusion of sealing member  125  into annular space  165  as sealing member  125  continues to expand. Moreover, sealing member  125  does not extrude into annular space  195  due the passage of drilling fluid therethrough. The pressure of the drilling fluid acts on scaling element  125 , pushing and deforming the compliant sealing element  125  away from annular space  195 . With potential extrusion paths blocked, further expansion of sealing member  125  is instead accommodated by inner preload ring  135  and outer preload ring  145  as well as the compliant nature of angular ring  140  and resilient ring  130 . By accommodating continued thermal expansion of sealing element  125  in this manner, sealing member  125  is prevented from over-compression to the point where sealing member  125  becomes damaged and loses it resiliency. 
     When temperatures surrounding seal  100  subsequently decrease, such as when drilling ceases, and sealing member  125  cools, sealing member  125  contracts. Despite its contraction, sealing member  125  remains in sealing engagement with surfaces  160 ,  180  due to preloading of seal  100  and continues to provide a barrier preventing drilling fluid from entering annular space  165  between insert  105  and tubular  110 . 
     Turning now to  FIG. 4 , another embodiment of an anti-extrusion seal is depicted between a tubular  210  and an insert  205  disposed therein. In some embodiments, tubular  210  is a component of a drill string for creating a well bore, such as but not limited to a drill collar, and insert  205  is a chassis within which electronics (not shown) for downhole measurements are positioned. Seal  200  is seated in a groove  215  disposed in the outer surface  220  of insert  205  and, when preloaded as will be described, provides a barrier to fluid flow into an annular space  265  between insert  205  and tubular  210 . Seal  200  includes a compliant sealing member  225  and a pair of angular rings  230 ,  240 . 
     Sealing member  225  is compliant or flexible, and in some embodiments, comprises elastomeric material. Thus, sealing member  225  deforms in response to pressure loads, such as pressure loads from drilling fluid passing through tubular  210  and insert  205  disposed therein. Further, sealing member  225  is responsive to temperature change. As such, sealing member  225  expands when exposed to temperatures exceeding the ambient temperature, and contracts again when exposed to lower temperatures. 
     Moreover, sealing member  225  has a height or thickness  267  which exceeds the radial clearance between an outer surface  260  of insert  205  and an inner surface  280  of tubular  210 . Consequently, sealing member  225  must be compressed to fit between insert  205  and tubular  210  as shown. This causes sealing member  225  to contact both inner surface  280  of tubular  210  and axially extending surface  260  of insert  205 , thereby forming a barrier which prevents drilling fluid that may enter groove  215  from bypassing sealing member  225  and entering an annular space  265  between insert  205  and tubular  210 . 
     Compressing sealing member  225  in this manner preloads seal  200 . In contrast to the previous embodiment, compression of sealing member  225  between insert  205  and tubular  210  provides all of the preloading to seal  200 . Preloading of seal  200  occurs at ambient temperature, when sealing member  225  assumes its natural state in the absence of thermal expansion. When seal  200  is subsequently exposed to increased temperatures, sealing member  225  expands, thereby increasing its ability to prevent drilling fluid from entering annular space  265 . When temperatures surrounding sealing member  225  later decrease, sealing member  225  contracts. However, because seal  200  was preloaded when sealing member  225  was is in its natural, unexpanded state, sealing member  225  remains in contact with surfaces  260 ,  280  and thus continues to provide a barrier to fluid flow into annular space  265  even in the absence of thermal loads from, for example, heat generated by drilling. 
     Groove  215  of insert  205  is bounded by axially and radially extending surfaces  260 ,  255 , respectively, of insert  205 . Inner angular ring  230  is slideable over axially extending surface  260  of insert  205 , and outer angular ring  240  is slideable over radially extending surface  255  of insert  205 . Further, inner angular ring  230  has an angled outer surface  235  configured to receive a complimentary angled inner surface  245  of outer angular ring  240 . Outer angular ring  240  is slideable over angled outer surface  235  relative to inner angular ring  230 . Similarly, inner angular ring  230  is slideable over angled inner surface  245  relative to outer angular ring  240 . 
     As previously described, sealing member  225  expands when exposed to temperatures higher than ambient, and subsequently contracts when surrounding temperatures decrease. When sealing member  225  expands against inner angular ring  230 , inner angular ring  230  slides along surface  260  of insert  205  away from sealing member  225 . In response, outer angular ring  240  is displaced by inner angular ring  230  radially outward due to the angled nature of surfaces  235 ,  245  and the interaction of outer angular ring  240  with radially extending surface  255  of insert  205 . Conversely, when sealing member  225  contracts away from inner angular ring  230  and the compressive force on outer angular ring  240  exceeds that exerted by sealing member  225  on inner angular ring  230 , outer angular ring  240  displaces radially inward. In response, inner angular ring  230  is displaced by outer angular ring  240  along surface  260  of insert  205  toward sealing member  225 . 
     Further, inner and outer angular rings  230 ,  240 , when assembled as shown, are interfered, or overlap, as indicated by dotted line  250 , which represents a portion of radially outer surface  235  of ring  230 . As shown, inner and outer angular rings  230 ,  240  are interfered, or overlap, by a distance or interference  285 . The dimensions of rings  230 ,  240  are selected such they remain overlapped to a degree (meaning overlap  285  is greater than zero) once installed between insert  205  and tubular  210 . As such, inner and outer angular rings  230 ,  240  do not separate despite relative movement, thereby preventing an annular space from opening between inner and outer angular  230 ,  240  that may provide an extrusion path for sealing member  225 . 
     Inner and outer angular rings  230 ,  240 , respectively, are both made of compliant material. Hence, these components  230 ,  240  are deformable under contact loads from sealing member  225  and pressure loads from drilling fluid entering groove  215 . Also, the compliant nature of angular rings  230 ,  240  permits limited expansion of sealing member  225 . By allowing sealing member  225  some room to expand, sealing member  225  is prevented from being compressed or squeezed during expansion to point where sealing member  225  becomes damaged and loses it resiliency. 
     As previously described, tubular  210  may form a portion of a drill string for creating a well bore, and electronics (not shown) disposed within insert  205 , and protected by seal  200 , may perform downhole measurements. During assembly of the drill string, seal  200  is first assembled within groove  215  between insert  205  and tubular  210  prior to run-in of the drill string, including tubular  210 , into the borehole. To assemble seal  200 , angular ring  230  disposed within groove  215  abutting surfaces  255 ,  260 , as shown in  FIG. 4 . Next, angular ring  240  is positioned radially outward of and in interference with angular ring  230 . Sealing member  225  is then positioned within groove  215  between insert  205  and tubular  210  abutting angular rings  230 ,  240 . Positioning sealing member  225  between insert  205  and tubular  210  preloads sealing member  225  because sealing member  225  must be squeezed or compressed to fit between insert  205  and tubular  210 . Assembly of seal  200  is then complete. Tubular  210  with insert  205  positioned therein may then be lowered into the borehole as part of the drill string. 
     During drilling operation, drilling fluid is delivered through the drill string, including tubular  210 , to the drill bit. Due to its weight, the drilling fluid is highly pressurized and will pass through any exposed spaces between insert  205  and tubular  210 , such as the annular space  295  between inner surface  280  of tubular  210  and insert  205 . Even so, sealing member  225  prevents the drilling fluid from bypassing sealing member  225  and entering annular space  265  between insert  205  and tubular  210  due to preloading of seal  200 . 
     The temperature of sealing member  225  may also begin to rise in response to heat generated by drilling or increased downhole temperatures. As a result, sealing member  225  expands against angular ring  230 , thereby displacing angular ring  230  along axially extending surface  260  of insert  205 , as illustrated by  FIG. 5 . In turn, angular ring  230  displaces outer angular ring  240  radially outward due to the angled nature of surfaces  235 ,  245 . As outer angular ring  240  displaces radially outward, a gap  275  between outer angular ring  240  and inner surface  280  of tubular  210  closes. 
     Referring now to  FIG. 6 , continued expansion of sealing member  225  displaces angular rings  230 ,  240  such that gap  275  is closed and angular ring  240  is compressed against inner surface  280  of tubular  210 . Once gap  275  is closed, angular ring  240  prevents extrusion of sealing member  225  into annular space  265  as sealing member  225  continues to expand. Moreover, sealing member  225  does not extrude into annular space  295  due the passage of drilling fluid therethrough. The pressure of the drilling fluid acts on sealing element  225 , pushing and deforming the compliant sealing element  225  away from annular space  295 . With potential extrusion paths blocked, further expansion of sealing member  225  is instead accommodated by the compliant nature of angular rings  230 ,  240 . By accommodating continued thermal expansion of sealing element  225  in this manner, sealing member  225  is prevented from over-compression to the point where sealing member  225  becomes damaged and loses it resiliency. 
     When temperatures surrounding seal  200  decrease, such as when drilling ceases, and sealing member  225  cools, sealing member  225  contracts. Despite its contraction, sealing member  225  remains in sealing engagement with surfaces  260 ,  280  due to preloading of seal  200  and continues to provide a barrier preventing drilling fluid from entering annular space  265  between insert  205  and tubular  210 . 
     While preferred embodiments of this invention have been shown and described, modifications thereof can be made by one skilled in the art without departing from the scope or teaching of this invention. The embodiments described herein are exemplary only and are not limiting. Many variations and modifications of the system and apparatus are possible and are within the scope of the invention. For example, the relative dimensions of various parts, the materials from which the various parts are made, and other parameters can be varied, so long as the methods and apparatus retain the advantages discussed herein. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims.