Abstract:
Embodiments of the present invention provide a process for manufacturing swellable packers with reinforcing fabrics and associated products used for sealing off chambers within well bores. According to one embodiment, the swellable packer is formed around a pipe by embedding a sheet of the reinforcing fabric within layers of a swellable polymer wrapped around the pipe. A sheet of reinforcing fabric is situated near each end of the swellable packer. Thus, as exposure to oil or water will cause the swellable packer to expand, the reinforcing fabric will initially retard swelling at the ends to allow for greater initial swelling along the center portion. The reinforcing fabric also strengthens the polymer to resist tearing or breakage caused by the flow of oil or water. A pair of swellable packers according to embodiments of the present invention can be placed on a pipe and placed within a bore and exposed to oil or water to create a pressurized chamber.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present invention claims priority from U.S. Provisional Patent Application No. 61/349,044, filed on May 27, 2010, which is incorporated herein by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to improved manufacturing processes for downhole packers and associated products, and in particular downhole packers that have improved sealing characteristics. 
       BACKGROUND OF THE INVENTION 
       [0003]    In the oil and natural gas industries, a bore is typically formed into the earth to define a well, and oil or natural gas is withdrawn from the well. However, over time, the level of production from these wells can decrease and, as a result, several methods have been developed for increasing the oil or natural gas withdrawn from the well. 
         [0004]    One of these methods involves sealing a section of the bore wall at a location above the bottom of the well. In particular, one or more plugs can be placed along the depth of the bore that seal against the bore wall. Between two of these plugs, or between one plug and the top or the bottom of the well, a chamber can be defined. These chambers are then subjected to very high pressures of water or other fluids so as to cause the walls of the bore to fracture. This can create additional flow of oil or natural gas into the chamber after the pressure is released. 
         [0005]    Conventionally, these plugs have been formed of concrete or other cementitious materials. However, the concrete can degrade over time and leak. To improve upon concrete plugs, the industry has developed swellable packers made from polymers that swell when exposed to oil and/or water. The swellable packer is sized to have an outer diameter just smaller than the diameter of the bore and then it is placed down the bore in an unswelled state. Oil or water is then brought into contact with the swellable packer. However, pressure from the impact of oil or water may cause pieces of polymer to tear or break away. The polymer of the swellable packer begins to swell as it takes on the oil or water. This swelling causes the swellable packer to seal against the wall of the bore and create a seal so that pressurized chambers can be defined for fracturing the bore wall. 
         [0006]    One measure of performance of these swellable packers is the amount of pressure to which the pressurized chambers can be exposed before the swellable packers begin to leak. Chamber pressures of at least 4,000 psi are achievable with conventional technology. However, it is desirable to achieve even higher chamber pressures, to allow more oil or gas production. 
       BRIEF SUMMARY OF THE INVENTION 
       [0007]    These and other advantages are provided by the swellable downhole packers and improved processes of manufacturing provided by the present invention. Advantageously, embodiments of the present invention provide a reinforcing fabric in conjunction with a swellable polymer to provide improved sealing pressures. The reinforcing fabric according to one embodiment is provided at the ends of the swellable packers and can retard swelling of the swellable polymer at those locations. This retardation of the swelling at the ends of the packers allows for more swelling along the center portion of the packer before the ends of the packer are fully swollen. As such, improved sealing pressures are achievable. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein: 
           [0009]      FIG. 1  is a partially sectional view of an oil or gas well showing the position of two swellable packers in a bore; 
           [0010]      FIG. 2  is a perspective view of a swellable packer according to embodiments of the present invention; 
           [0011]      FIG. 3  is an expanded and partially sectioned view of one end of a swellable packer according to embodiments of the present invention; and 
           [0012]      FIG. 4  is a plan view of a reinforcing fabric according to embodiments of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0013]    The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the inventions are shown. Indeed, these inventions may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout. 
         [0014]    Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation. 
         [0015]      FIG. 1  illustrates an oil or natural gas well that defines a bore  12 . Positioned in the bore  12  are two swellable packers  10 . These swellable packers  10 , when fully swollen, create a chamber  18  that can be pressurized between the swellable packers. The swellable packers  10 , in the illustrated embodiment, are both supported on a support tube  11 . This support tube  11  can be made of a steel pipe or any other suitable material. In some embodiments, the support tube  11  could be used as a conduit for oil, gas or other fluids, and/or could be used for allowing other downhole components to extend down the bore. The support tube  11  may also be completely or partially blocked along its length. 
         [0016]      FIG. 2  is a closer view of one of the swellable packers  10 . The swellable packer  10  of the illustrated embodiment is comprised of a swellable polymer  13  that is secured to the support tube  11 . The swellable packer  10  should define a length along the support tube  11  sufficient to adequately seal the bore, and in one embodiment this length may be 24″. The swellable packer may be provided with end caps  14  at one or both ends of the swellable packer. The end caps  14  can be formed of metal or other resilient material and have a chamfered or tapered portion (as best seen in  FIG. 3 ) that helps guide the swellable packer  10  through the bore as the support tube  11  is lowered or raised in the bore. 
         [0017]    According to embodiments of the present invention, the swellable polymer  13  can be applied to the support tube  11  by wrapping a continuous sheet of swellable polymer around the support tube so as to define multiple layers. The first layer of the swellable polymer  13  can be secured to the support tube with a bonding agent. One bonding agent that is effective is THIXON 532-A-EFAPH available from Dow Chemical. 
         [0018]    In an exemplary embodiment, a sheet of swellable polymer material is 24″ in width and is wrapped around the support tube 16 times. The thickness of the sheet of swellable polymer according to one embodiment is 0.045″, although the thickness of the sheet can increase as the winding around the support tube  11  continues. After the wrapping process has been finished, the swellable polymer  13  can be subjected to a curing process such as in a steam autoclave. This curing process can cause the various wrapped layers to bond together and define a substantially homogeneous thickness to the swellable polymer. 
         [0019]    One particularly advantageous swelling polymer  13  is available from Tendeka under model no. JSSEO-5. This proprietary formulation provides strong swelling and sealing characteristics. However, other swellable polymers from other manufacturers could be used in embodiments of the present invention. 
         [0020]    To achieve a desired tolerance on the outside diameter of the cured swellable packer, the swellable polymer  13  (while supported on the support tube  11 ) can be subjected to a machining operation, such as turning on a lathe. The end caps  14  can then be placed over the ends of the swellable polymer  13  and bonded in place with the bonding agent. 
         [0021]    When swellable packers  10  are placed in a bore and exposed to oil or water to initiate the swelling process, the inventors have recognized that the swelling begins at the end portions  19  of the swellable polymer that are first exposed to the oil or water. The swelling process is not instantaneous and so, as the swelling proceeds, the end portions  19  of the swellable polymer  13  swell faster than central portion  20  of the swellable polymer. The inventors have recognized that this sequence can have a deleterious effect on the overall sealing pressure of the swellable packer because the central portion of the swellable polymer  13  may not swell as much as the end portions  19  of the swellable polymer. As such, the outward pressure exerted on the bore wall will not be uniform along the length of the swellable packer  10 , and will he higher at the end portions  19  of the swellable packer exposed to the oil or water. Thus, the configuration of a conventional swellable packer does not allow the swellable polymer to fully swell along its length. The end portions  19  seal the central portion  20  from receiving sufficient oil or water to fully swell. 
         [0022]      FIG. 3  is an expanded and partially sectioned view of one end of a swellable packer  10  according to embodiments of the invention. The illustrated end of the swellable packer  10  includes a reinforcing fabric  15  extending along a length at the end of the swellable packer. The reinforcing fabric  15  is positioned in the illustrated embodiment at a depth below the outer surface of the swellable polymer  13 . In one embodiment, the reinforcing fabric  15  is inserted during the winding process for the sheet of swellable polymer after a first section of sheet has been wrapped but before a second section is wrapped. For example, the reinforcing fabric  15  is inserted after the 12 th  wrap of 16 total wraps has been completed. This forms a swellable pack including an inner annulus of swellable polymer radially inward of the reinforcing fabric and an outer annulus of swellable polymer radially outward of the reinforcing fabric. In some embodiments, the reinforcing fabric  15  has a bonding agent applied thereto to bond with the swellable polymer. 
         [0023]    In one embodiment of the manufacturing method according to the present invention, the reinforcing fabric  15  is first positioned between two sheets of swellable polymer and then the assembly is calendered to define a sandwich structure having a thickness of approximately 0.040″. This sandwich structure is then inserted during the wrapping process. The sandwich structure has more flexural strength than the reinforcing fabric  15  by itself, which makes it easier to insert during the wrapping process. 
         [0024]    In addition, in some embodiments, the reinforcing fabric  15  may not extend all the way to the end face of the swellable polymer  13  so as to be fully encapsulated within the swellable polymer. If the reinforcing fabric  15  extends all the way to the end face, it could present a possibility for the portion of the swellable polymer radially outside of the reinforcing fabric  15  to swell disproportionately more quickly than the portion radially inside of the reinforcing fabric because oil or water would have an additional path (i.e. along the fabric) to cause swelling. In some circumstances, this could cause delamination and failure of the swellable packer. In one embodiment, the reinforcing fabric  15  is one-third the length of the swellable polymer  13 , as measured along the axis of the support tube  11 , and the reinforcing fabric  15  ends 0.125 inches from the end cap  14 . As illustrated, the reinforcing fabric  15  can be 3 inches in length. 
         [0025]    One embodiment of reinforcing fabric is shown in more detail in  FIG. 4 , and includes relatively stronger fibers  16  extending in a warp direction and relatively weaker fibers  17  extending in a weft direction. The reinforcing fabric  15  is positioned during the manufacturing process so that the relatively stronger fibers  16  are aligned with the axis of the support tube  11  and the weaker fibers  17  extend generally circumferentially around the axis of the support tube  11 . However, the fibers of the reinforcing fabric may have the same tensile strength in both the warp and weft directions, and in another embodiment, the fibers extending in one direction, such as the warp direction, may be more densely spaced than in the other direction. 
         [0026]    As oil or water is introduced into the bore to begin the swelling process, the oil or water is first contacted against the end portions  19  of the swellable polymer. The reinforcing fabric  15  strengthens the end portions  19  and prevents the swellable polymer from tearing or breaking away. Furthermore, rather than swelling at a rate faster than the central portion  20  of the swellable polymer, the reinforcing fabric  15  retards the swelling process by mechanically restraining the end portions  19  of the swellable polymer from swelling more quickly than the central portion  20 . This retardation of the swelling of the end portions  19  allows the central portion  20  of the swellable polymer to swell at a comparable rate and thus create a tighter seal against the walls of the bore. 
         [0027]    According to some embodiments of the invention, after some swelling of the end portions  19  has occurred, the relatively weaker fibers  17  can rupture, thus allowing the relatively stronger fibers  16  to separate in a circumferential direction and then the swelling of the end portions of the swellable polymer to continue without circumferential retardation. The relatively stronger fibers help reinforce the swellable polymer  13  after it has swollen, which is advantageous because the strength of the polymer decreases when it is swollen. Thus, after the installation process has been completed, the amount of swelling exhibited by the swellable polymer is more uniform along its length than in conventional packers, thus creating a stronger seal. Indeed, sealing pressures of up to 7,500 psi have been achieved with a 6 foot length of the swellable packer having reinforcing fabric 24 inches long at each end. Such a sealing pressure is of great benefit to the oil and gas industry and allows improved production of oil and gas wells. 
         [0028]    In the embodiment depicted in  FIG. 4 , the reinforcing fabric  15  is a cloth material. In another embodiment, the reinforcing fabric  15  can comprise tire cord, and in particular nylon fabric intended for use in the construction of tires. One commercially-available product that is suitable is LNF085, a nylon leno weave available from Firestone Fibers &amp; Textiles Company in Kings Mountain, N.C. However, in various other embodiments, the reinforcing fabric may be formed of other types of material, such as wire, carbon fibers, basalts, etc. 
         [0029]    Although a single strip of reinforcing fabric  15  is illustrated at both ends of the swellable packer  10 , other embodiments include multiple layers of reinforcing fabric and layers of reinforcing fabric extending further along the length of the swellable packer  10 . In order to achieve a more uniform swell profile after installation, some embodiments of the invention include two layers of reinforcing fabric at the ends of the swellable packer, a single layer of reinforcing fabric adjacent to those end portions, and a central portion with no reinforcing fabric provided. A more uniform swell profile may also be provided by reinforcing fabrics that have circumferential strength that varies along the length of the fabric.