Patent Publication Number: US-2010122820-A1

Title: Seal Arrangement for Expandable Tubulars

Description:
BACKGROUND OF THE INVENTION 
     Conventionally when a wellbore is created, a number of casings are installed in the borehole to prevent collapse of the borehole wall and to prevent undesired outflow of drilling fluid into the formation or inflow of fluid from the formation into the borehole. The borehole is drilled in intervals whereby a casing which is to be installed in a lower borehole interval is lowered through a previously installed casing of an upper borehole interval. As a consequence of this procedure the casing of the lower interval is of smaller diameter than the casing of the upper interval. Thus, the casings are in a nested arrangement with casing diameters decreasing in downward direction. Cement annuli are provided between the outer surfaces of the casings and the borehole wall to seal the casings with the borehole wall. As a consequence of this nested arrangement a relatively large borehole diameter is required at the upper part of the wellbore to achieve the desired flowbore diameter extending down through the well. Such a large borehole diameter involves increased costs due to heavy casing handling equipment, large drill bits, and increased volumes of drilling fluid and drill cuttings. Moreover, increased drilling rig time is involved due to required cement pumping, cement hardening, required equipment changes due to large variations in hole diameters drilled in the course of the well, and the large volume of cuttings drilled and removed. 
     Expandable tubulars may also be used to repair, seal, or remediate perforated existing casing that has been parted, corroded, or otherwise damaged since installation. Whether used as a liner or to initially line a wellbore, sealing between overlapping portions of the tubulars is important to prevent fluids contained in the wellbore from leaking into the surrounding formation, or vice versa. 
     SUMMARY OF INVENTION 
     In one aspect, the present disclosure relates to an expandable tubular. The expandable tubular includes a tubular body and a sealing arrangement disposed on an external surface of the tubular body. The sealing arrangement includes a plurality of seals having a corrugation. 
     In another aspect, the present disclosure relates to a method of manufacturing a sealing arrangement for an expandable tubular. The method includes arranging a plurality of seals about the circumference of an expandable tubular and forming corrugations in the plurality of seals such that the effective length of the plurality of seals is at least 5 percent greater than the circumference of the expandable tubular. 
     In another aspect, the present disclosure relates to a sealing assembly for an expandable tubular. The sealing assembly includes a tubular body having an outer circumference and a seal disposed on the outer circumference and having a contracted state wherein a centerline of the seal is greater in length than the outer circumference of the tubular body. 
     Other aspects and advantages of the invention will be apparent from the following description and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a partial cross-sectional view of a sealing arrangement on an expandable tubular in accordance with one embodiment. 
         FIG. 1B  is a partial cross-sectional view of the sealing arrangement shown in  FIG. 1A  after expansion of the expandable tubular. 
         FIG. 2  is an unwrapped view of a sealing arrangement in accordance with one embodiment. 
         FIG. 3  is an axial view of a seal in accordance with one embodiment. 
         FIG. 4  is an unwrapped view of a sealing arrangement in accordance with one embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure relates to apparatus and methods for sealing the outside of an expanded tubular in a wellbore. 
     Separate seals are typically provided on the outer circumference of an expandable tubular in order to seal against a cased or open hole wellbore in which it is expanded. As the tubular is expanded, the seals stretch with the outer circumference of the expandable tubular and are pressed against the inside of the wellbore, which may be the formation itself or the inside of a previously installed tubular. The expansion ratio of an expandable tubular may be, for example, 10 percent to 20 percent, or more. Before expansion, the seals are in close contact with the outside of the expandable tubular to protect the seals from damage during the deployment of the expandable tubular into the wellbore. During expansion, the seals surrounding the expandable tubular will stretch to an increased diameter, which may be in addition to the stretching of the seals during installation prior to expansion. Many seal materials can handle such stretching and provide reliable seals, but seal materials intended for high pressure and/or high temperature applications are usually less ductile, making the seals more susceptible to rupturing or tearing during the expansion process. Examples of high temperature sealing materials include asbestos wrapped with metal, Viton® (DuPont Performance Elastomers, Wilmington, Del.), and Kalrez® (DuPont Performance Elastomers, Wilmington, Del.). 
     In  FIGS. 1A and 1B , there is shown a sealing arrangement  119  for an expandable tubular  101  in accordance with one embodiment. The sealing arrangement  119  includes a plurality of seals  120   a - d  having a contracted state where the centerline  118   a , equidistant between the upper and lower edges of the seal, does not form a circle and an expanded state where the centerline  118   b  forms substantially a circle. In embodiments, the seals  120   a - d  may have at least one transverse corrugation. As used herein, a “corrugation” in the seal means that a fold, a wave, or other axial or transverse bend exists in the seal so that the seal is not a constant 360 degree ring and forms the contracted state. In one embodiment, each of the seals  120   a - d  includes a plurality of transverse corrugations in a repeating pattern around the seal, such as, for example, a transverse sinusoidal pattern, as shown in  FIG. 1A . The corrugations of each seal  120   a - d  may be nested with an adjacent seal, as shown in  FIG. 1A . The corrugations allow for centerline  118   a  of the inside surface of the seals  120   a - d  in the contracted state to have a greater effective length than the circumference of the expandable tubular  101  before expansion. 
       FIG. 1B  shows the embodiment of  FIG. 1A  after expansion of the expandable tubular  101 . During expansion, the seals  120   a - d  are expanded from their contracted state to their expanded state whereby the corrugations of the seals  120   a - d  straighten out such that centerline  118  of the seals  120   a - d  tends to be more circular and conform to the external surface of the expanded tubular  101 . The length of the centerline  118  is greater than the outer circumference of the tubular  101 . Upon full expansion of the expanded tubular  101  into contact with the wellbore, previously installed tubular  110  in this embodiment, the sealing arrangement  119  forms a sealing interface with the inside of previously installed tubular  110 . As a result of the corrugations, the seals  120   a - d  effectively have a lower expansion ratio than the expandable tubular  101 . For example, the seals  120   a - d  may have an expansion ratio of 5 percent while the expandable tubular  101  has an expansion ratio of 10 percent. Accordingly, less ductile sealing materials that can withstand high temperatures and pressures may be used to form the seals  120   a - d  in order to provide a high temperature and/or high pressure seal between the outside of the expanded tubular  101  and the wellbore such as the inside of the previously installed tubular  110  or borehole wall. 
     Returning to  FIG. 1A , the sealing arrangement  119  may further include a lower protective ring  121  and an upper protective ring  122  to minimize or prevent damage to the seals  120   a - d  while running the expandable tubular  101  into the wellbore. Additionally, the protective rings  121  and  122  maintain the seals  120   a - d  in place during installation and then expansion of the expandable tubular  101 . The protective rings  121  and  122  may be formed from various metals, durable plastics, or other materials that are sufficiently strong to withstand abrasion and impact during running of the expandable tubular  101 , but not so strong that the protective rings  121  and  122  interfere with the expansion of the expandable tubular  101 . In one embodiment the protective rings  121  and  122  may be cut so that the protective rings  121  and  122  split during the expansion process. Those having ordinary skill in the art will appreciate that the present invention is not limited to any particular expansion method. For example, expansion may be carried out using an expansion cone that is mechanically pulled or driven by fluid pressure. 
     In  FIG. 2 , an unwrapped view of another sealing arrangement  200  is shown in accordance with one embodiment.  FIG. 2  demonstrates a method that may be used to assemble the sealing arrangement  200  with an expandable tubular. Instead of being continuous rings, the seals  201   a - d  are strips of sealing material that are wrapped around the expandable tubular prior to running into the well. Wrapping avoids the need to slide the seals  201   a - d  from the ends of the expandable tubular to the desired sealing location. Wrapping also provides more control over forming the corrugations in the seals  201   a - d . To assemble the sealing arrangement shown in  FIG. 2 , each seal  201   a - d  is wrapped around the expandable tubular such that the opposing ends of each seal  201   a - d  are in close proximity. An adhesive resin may then be applied to keep the ends of each seal  201   a - d  together. The corrugations may be formed as part of a mold of strips. In one embodiment, the length of the strips may be selected to be about 5 to about 10 percent greater than the circumference of the expandable tubular. During assembly and after the opposing ends of the strips are adhered to each other, the excess length of the strips may be displaced axially to form the transverse corrugations. To prevent loose material from being snagged, an adhesive may be applied at selected locations or across the strips in order for the strips to remain against the outer surface of the expandable tubular. 
     To reduce or eliminate the risk of a leak path, the locations of the opposing ends of each seat  201   a - d  about the circumference of the tubular  101  may be staggered, as shown in  FIG. 2 . In this embodiment, the locations of the opposing ends of each seal  201   a - d  are staggered at about 180 degrees apart. For example, seal  201   a  has its opposing ends at 90 degrees, seal  201   b  at 270 degrees, seal  201   c  at 90 degrees, and seal  201   d  at 270 degrees. The staggering of adjacent seals may be repeated in a pattern to accommodate additional seals and may vary in angle. A repeating pattern is not necessary to provide the benefits of preventing a leak path, but does provide an orderly process for insuring adjacent seals do not have their ends in close proximity to each other. Although only four seals are shown, many more seals may be used. For example, in one embodiment, 50 to 100 seals may be used over a 2 foot interval. Each seal may be, for example, 0.1 inch in thickness. 
     In  FIG. 3 , an axial view of a seal  301  is shown in accordance with one embodiment. The seal  301  includes a plurality of radial corrugations that repeat in a sinusoidal pattern in the contracted state. As with the transverse corrugations in the other embodiments, the radial corrugations straighten out in their expanded state during expansion to provide a seal between the expanded tubular and the wellbore. 
     In  FIG. 4 , an unwrapped view of another sealing arrangement  400  is shown in accordance with one embodiment. In this embodiment, the sealing arrangement  400  includes a plurality of seals  401   a - e , each of which includes one transverse corrugation. The seals  401   a - e  may be continuously formed, or applied as strips as discussed above with respect to  FIG. 2 . As with other sealing arrangements disclosed above, the single transverse corrugation will straighten out during the expansion process. 
     In operation, the seals  120   a - d  are disposed on the expandable tubular  101 . The seals are in their contracted state with their centerline  118  having a length greater than the circumference of the outer surface of the expandable tubular  101  on which the seals are disposed. The expandable tubular  101  is then expanded. As the tubular  101  is expanded, the corrugations straighten out around the tubular  101 , passing through a transition state, to the expanded state where the centerline  118  of the seals  120   a - d  forms a circle. The seals  120   a - d  are then further expanded in their expanded state to increase the length of the centerline  118  and their outer circumference. The seals  120   a - d  are then compressed between the expandable tubular  101  and the wellbore to their final expansion state to establish a seal between the expandable tubular  101  and the wellbore. 
     Embodiments disclosed herein may be particularly suitable for high temperature (e.g., greater than 300° F.) installations of expandable tubulars. In general, sealing materials suitable for high temperature applications are less ductile than other sealing materials. To reduce the stretching of the less ductile sealing materials, one or more corrugations may be formed in at least one seal on the expandable tubular in accordance with one or more embodiments. One such high temperature application is in repairing steam injection wells in steam-assisted gravity drainage (SAGD) and cyclic steam stimulation (CSS) projects. The SAGD process is a form of enhanced oil recovery that involves injecting steam into an oil bearing formation in order to lower the viscosity of the oil so that it drains into a producing well. The SAGD process involves a pattern of wells that are injecting steam or producing the oil. If a well is damaged such that it leaks, it is taken out of production to avoid ecological damage, which reduces the production of the pattern of wells. CSS, also known as “huff and puff,” involves repeating intervals of steam injection, soaking of the formation with the steam, then production of hydrocarbons from the same well. 
     Expandable tubulars can be used to repair such wells by expanding a tubular member across and sealing above and below the damaged portion of the casing in the well. Because of the steam injection, the seals on the expandable tubular are subjected to periods of intense heat that can degrade the seals. One solution that has been considered is a metal-to-metal seal directly between outer surface of the expanded tubular and the inside of the previously installed casing. However, metal-to-metal seals are unreliable because of eccentricity of the casing already in the well, either from the original manufacture of the casing or from the damage that led to the need for repair. The expanded tubular is formed into a nearly perfect circle during expansion, but the eccentricity of the casing can result in a gap between the outside of the expanded tubular and the inside of the casing. Corrugating a seal made with sealing material that can withstand higher temperatures may provide the sealing performance necessary to repair and seal SAGD wells and other high temperature wells. The corrugations reduce the stretching imposed on the seals during the expansion process, thereby allowing for the use of less ductile seals on the expandable tubular. 
     Although this detailed description has shown and described illustrative embodiments of the invention, this description contemplates a wide range of modifications, changes, and substitutions. In some instances, one may employ some features of the present invention without a corresponding use of the other features. Accordingly, it is appropriate that readers should construe the appended claims broadly, and in a manner consistent with the scope of the invention.