Abstract:
The present invention is a composition for forming seals. The composition includes a base material and a hydrogel. The base material is preferably an elastomer or a thermoplastic. Seals formed with the composition are particularly suited for use in a wellbore environment. The inclusion of hydrogel in the seals allows the seals to be manipulated or altered through certain environmental factors. For instance, temperature, oil/water ratio, pH and the electronic field may all be used to alter the characteristics of the hydrogel. In this way, the seal may be caused to swell in response to a specific stimulus, thereby preventing or sealing a leak without requiring additional work or input from the operator.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims the benefit of U.S. Provisional Application Ser. No. 60/541,035, filed on Feb. 2, 2004, and is a Continuation-In-Part of and also claims the benefit of U.S. patent application Ser. No. 10/789,846, filed on Feb. 27, 2004. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates generally to seals for oilfield applications. More specifically the present invention describes the use of hydrogel in seal bodies for downhole use.  
         [0004]     2. Description of the Prior Art  
         [0005]     Seal bodies, including o-rings, packer elements, Chevron seals, gaskets, etc., are widely used for numerous downhole oilfield applications. One ongoing issue in this area is how to energize seals and maintain sealing forces throughout seal service life. Capital loss or remediation associated with seal failure can be tremendous in certain operation areas.  
         [0006]     One conventional method to energize seals is to utilize mechanical force to deform the seal between sealing surfaces. For seals with large cross-section and/or large sealing gaps, satisfactory sealing performance is hard to achieve due to limited mechanical force. The other major problem encountered during operation is the relaxation of contact force between the seal and the sealing surfaces. This is caused primarily by the viscoelastic nature of polymeric materials used in conventional seals.  
         [0007]     Another technique for improving seals involves the use of a pressure activated sealant that is specifically designed to seal leaks in wells and severe-environment hydraulic systems. The sealant functions by causing a pressure drop through a leak site, which in turn causes the sealant fluid to polymerize into a flexible solid seal. However, the major drawback of this technique is it requires a service engineer and a special tool to deliver the sealant to the leak site and complete the job. At that time, a significant amount of damage may have already occurred. Another disadvantage is that often tools which are installed 20,000 ft deep in the well where it is difficult and inefficient to deliver the sealant to the exact location where the leak occurs. Yet another drawback of this technique is that the sealant only starts to polymerize after a leak occurs. In certain cases, where the leakage is catastrophic, operation can fail before the polymerization process is completed.  
         [0008]     Hydrogel technology has been rapidly developed in medical industry due to its unique response to environmental changes such as pH value, salinity, electrical current, temperature and antigens. Hydrogel is a flexible, rubber-like and solvent-swollen polymer. In an aqueous environment, hydrogel can undergo a reversible phase transformation that results in dramatic volumetric swelling and shrinking upon exposure and removal of a stimulus. A property common to all gels is their unique ability to undergo abrupt changes in volume. Gel can swell or shrink as much as 1000 times in response to small external condition changes. Through the conversion of chemical or electrical energy into mechanical work, a number of device have already been constructed which can produce forces up to 100 N/cm 2  and contraction rate on the order of a second. Using microscale hydrogel, the volumetric transition can occur within minutes or even seconds. The favorable scaling of hydrogel dynamic has been the essential element in the development of micro-fluidic devices that employ hydrogel valves for flow control. One major benefit of these devices is that they are completely autonomous and therefore require no external power source.  
       SUMMARY OF THE INVENTION  
       [0009]     The present invention provides an improved seal body composition for use with both dynamic and static seal applications. In particular, the invention provides a seal body composition that is useful for downhole wellbore applications, including, but not limited to, o-rings, packer elements, chevron seals and gaskets.  
         [0010]     A seal body which is prepared or formed in accordance with the present invention includes a hydrogel polymer incorporated or included as part of the seal body. In this way, the seal may be activated when certain environmental parameters are manipulated or changed. These environmental parameters may include water/oil concentration, differential pressure, temperature, pH, and electronic field. The hydrogel polymer may be embedded, coated, attached or blended with other seal components to form the seal. Commonly used seal body composition components may include elastomers, plastics or other materials known in the art.  
         [0011]     Once incorporated into the seal body, the hydrogel provides several advantages over typical seal body components. First, the hydrogel allows the seal to be energized via swelling. Since hydrogel can swell as much as 1,000 times in volume, high swelling force can be utilized to energize the main seal body as well as anti-extrusion device.  
         [0012]     The hydrogel may also allow potential leak paths to be sealed. Hydrogel swells in aqueous environment. That is, whenever it contacts an aqueous medium, it starts to absorb water and swell. For applications with hard-to-seal voids or surfaces, hydrogel can stop leak via swelling. Swelling leads to greater squeeze of main seal body. This, in turn, seals the leak path and prevents seal failure.  
         [0013]     Another feature of seals incorporating hydrogel is the ability of the seal bodies to be reset. That is, the seals may be provided in a first configuration, then upon exposure to a certain environmental parameter, the seal may change or take a second configuration. Upon removal of the certain environmental parameter, or upon exposure to yet another environmental parameter, the seal body may then return to it&#39;s original configuration. This characteristic is particularly beneficial in downhole applications where a resettable seal is required.  
         [0014]     These and other features of may be used employed either alone or in combination, depending on the specific nature of the application in which they are used. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]      FIG. 1  shows a three-rubber element array.  
         [0016]      FIG. 2  shows a garter spring element array.  
         [0017]      FIG. 3  shows a packer element array.  
         [0018]      FIG. 4  shows an o-ring with backup rings.  
         [0019]      FIG. 5  shows a t-seal.  
         [0020]      FIG. 6  shows a chevron seal stack.  
         [0021]      FIG. 7  shows a spring energized seal. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]     Seal bodies formed in accordance with the present invention comprise two primary elements: (1) a base material and (2) a hydrogel. The term “seal” as used herein means any apparatus or means for preventing, or significantly limiting, material transport from a particular wellbore zone or region of a formation, to another isolated zone within the wellbore, unless otherwise indicated of clear from the context in which it is used. The terms “seal body”, or “seal bodies”, means a physical structure placed in a wellbore for forming a seal in the wellbore once exposed to a particular external stimulus (factors, parameters) or combination of stimuli. The respective ratios of base material and hydrogel in the composition forming the seal body is determined the specific nature of the application in which the seal will be used. As previously mentioned, hydrogels can change their swelling behavior upon exposure to an external stimulus, such as pH, temperature, light, and electric field. Therefore, factors which may contribute to the selection of a proper ratio of base material to hydrogel may include the temperature to which the seal will be exposed, the pH at which the seal will be used, the nature of any chemicals the seal may come into contact with (including, for instance, the oil/water ratio), the differential pressure which the seal must withstand and the electronic environment of the application. Any number of these factors may effect the performance of the seal.  
         [0023]     The base material of the seal body composition is generally selected from any suitable material known in the industry for forming seals. Preferably, the base material is a polymer. More preferably, the base material is an elastomer or a thermoplastic. Elastomers that are particularly useful in the present invention include nitrile rubber (NBR), hydrogenated nitrile rubber (HNBR), carboxyl nitrile rubber (XNBR), silicone rubber, ethylene-propylene-diene copolymer (EPDM), fluoroelastomer (FKM, FEPM) and perfluoroelastomer (FFKM). Thermoplastics which are particularly useful in the present invention include Teflon®, polyetheretherketone, polypropylene, polystyrene and polyphenylene sulfide.  
         [0024]     As used herein the term hydrogel is a broad phrase referring in general to a polymer that swells when used in aqueous environment. Hydrogel polymers useful in the present invention are preferably formed of a crosslinked polymer network. When this polymer network is exposed or immersed in a suitable solvent, the polymer chains in the network become solvated. In certain cases, crosslinkers may be provided to prevent the complete mixing of the polymer chains and the solvent by providing an elastic restoring force that counters the expansion of the network.  
         [0025]     The polymer network of the hydrogel may be formed from any suitable polymeric material. In a preferred embodiment, the polymer network is formed from cross-linked polymers including water-soluble methylcellulose, cellulose acetate phthalate, and hydroxypropyl methylcellulose polymers, poly (ethylene oxide) polymers, guar and its derivatives, polyacrylamide, polyvinylpyrolidone, polyacrylic acid, polyvinylpyrolidone, oligo maleinate copolymers, oligo maleinate oligomers, allyl maleate oligomers, silicon-based materials, and flouro-silicone based materials. The polymer used to form the hydrogel may also be in a metal complex form.  
         [0026]     Seals described in the present invention comprise a base material, such as a polymer, and a hydrogel. The base material and hydrogel may be combined in any suitable ratio using any suitable method. In a preferred embodiment, polymer/hydrogel blends may be prepared using any of the following methods: (1) a solution process; (2) a mesophase mediated process; (3) physical mixing/compounding, (4) injection or extrusion, (5) in-situ polymerization or (6) melt processing. Curing methods may be any suitable method, but is preferably thermal curing, microwave radiation or electronic beam radiation. Chemical modification, such as branching or grafting, of the hydrogel may be performed prior to manufacturing of polymer/hydrogel blends to achieve optimum dispersion of the hydrogel polymer. In-situ polymerization can mean polymerization of monomers or oligomers forming the polymer, hydrogel, or both, where the polymerization occurs simultaneous with the mixing of the base material and hydrogel, simultaneous to the formation of the seal body, or simultaneous with both processes.  
         [0027]     Weight ratios of hydrogel to base material include any suitable amount of hydrogel to form a seal body with good swelling and resetting properties. Preferably, the ratio of hydrogel to base material is from about 10 to about 90 parts by weight hydrogel based upon 100 parts of base material. More preferably, the ratio of hydrogel to base material is from about 20 to about 70 parts by weight hydrogel based upon 100 parts of base material  
         [0028]     Any other materials useful in forming seal bodies known to those of skill in the art may be included. Examples of such materials include, but are not necessarily limited to, carbon black powder reinforcement, surfactants, catalysts, and the like.  
         [0029]     Without limiting the scope of the invention, the following examples show specific seal body configurations which may particularly benefit from the incorporation or inclusion of hydrogel in the seal body material.  
       EXAMPLE 1  
       [0000]     Packer Elements  
         [0030]      FIG. 1  shows three-piece rubber element array or packer element  10 , such as that commonly used in downhole packers. The packer elements are external packer seal bodies that seal the annulus space between tubing and casing (not shown). Elements are energized by axial deflection of the seal bodies after the packer is run into the hole. Commonly used packer elements typically consist of backup end rings  16  and a center seal or element  18 . The center seal  18  typically includes a ring  20  which establishes the inner diameter of the seal. Hydrogel may be included or incorporated into any or all of the seal body elements. The hydrogel allows the seal bodies to be energized in response to external stimuli, as previously described.  
         [0031]      FIG. 2  shows a garter spring element array  50 . The array  50  includes a main element or seal body  52 , a garter spring  54  and backup end rings  56 . The array also includes an ID ring  58 . Hydrogel may be included in any or all of the seal bodies of the array. As with the assembly of  FIG. 1 , the garter spring array also benefits from the inclusion of hydrogel seal body components by allowing them to respond to external stimuli.  
         [0032]      FIG. 3  shows yet another packer element array  100 . This array includes a main seal body  70 , backup seal bodies  72  and an ID ring  74 . As with the seal bodies shown in  FIGS. 1 and 2 , hydrogel may be included in any or all of the seal bodies.  
       EXAMPLE 2  
       [0000]     O-Ring  
         [0033]     O-rings are simple bi-directional static seal bodies. For high temperature and/or high pressure sealing applications, backup rings are used to prevent O-ring extrusion. As shown in  FIG. 4 , the o-ring  150  includes two backup rings  152  which are formed of thermoplastic materials blended with hydrogel polymer. The O-ring may also be formed of elastomers blended with hydrogel polymer. In this application, the hydrogel is able to seal off potential leak paths as well as keep the o-ring energized via swelling. These characteristics are not achievable with existing conventional rubber materials used for o-ring applications.  
       EXAMPLE 3  
       [0000]     T-Seal Bodies  
         [0034]     T-seal bodies are typically used as reciprocating bi-directional dynamic seals. As shown in  FIG. 5 , T-seal  200  including seal body  202  and retaining ring  204 . The seal body is formed of a hydrogel modified thermoplastic or elastomer. Hydrogel can seal off potential leak paths as well as keep the T-seal energized via swelling. These benefits are not achievable with existing conventional rubber materials used for T-seal application.  
       EXAMPLE 4  
       [0000]     Seal Stack/Packing  
         [0035]     Vee packing or chevron seal body stacks are multiple seal lip multi-component seal body sets that are energized by differential pressure. Seal stacks are also suited to internal dynamic seal applications. Most conventional packing stacks are combinations of softer elastomer parts and harder plastic parts. The incorporation of hydrogel in the seal elements allows any potential leak paths to be sealed, as well as keeping seal body stacks energized via swelling. This is not achievable with existing conventional rubber materials used for seal body stack applications.  
         [0036]      FIG. 6  shows a seal body stack  250  having first hydrogel/elastomer elements  252  and second hydrogel/plastic elements  254 . These first and second elements are preferably alternating, as shown. However, depending on the specific nature of the application any configuration of first and second elements may be used.  
       EXAMPLE 5  
       [0000]     Spring-Energized Seal Bodies  
         [0037]     Spring-energized seals are uni-directional seals and may be either static or dynamic. These seals combine the benefits of packing, as seen in vee or chevron seals and radial compression as seen in o-rings. As shown in  FIG. 7 , a spring-energized seal  300  will be made of hydrogel modified thermoplastic or rubber materials. Hydrogel can seal off potential leak path as well as keep seal energized via swelling which is not achievable with existing conventional rubber materials used for seal application.  
         [0038]     Examples 6 through 16 below illustrate useful compositions for forming some seal bodies comprising a hydrogel and a base material (i.e. rubber) according to the invention. In the examples below, .hydrogel/rubber mixtures are unfilled and filled with carbon black powder and based on Therban® 3446 hydrated nitrile butadiene rubber. The hydrogels used in examples 6 to 11 are based upon polyvinylpyrrolidone K 90. Examples 12 to 16 use a hydrogel composed of monomers which polymerized in situ during the formation of the seal composition, where the monomers are maleinate oligomers and allyl maleate oligomers with polar links content of 65%.  
         [0039]     Testing methods and parameters used to evaluate properties of the seal compositions were as follows: Strength, Relative Elongation, and Residual Elongation were determined using ASTM Test D412 at 23° C. in air medium; Shore A hardness was tested per ASTM Test D2240 at 23° C. in air medium; Change of mass after swelling in liquid media was evaluated according to ASTM Test D624 using a 2% by wt NaCl/25% by wt CaCl 2  water solution at temperature of 90° C.  
       EXAMPLES 6-11  
       [0040]     Polyvinylpyrrolidone Based Hydrogel  
                                                                                                                               Ingredients   Ex. 6   Ex. 7   Ex. 8   Ex. 9   Ex. 10   Ex. 11                                All ingredient amounts are given in parts by weight:            Therban ® 3446 (HNBR)   100   100   100   100   100   100       (hydrogenated acrylonitrile-butadiene       rubber available from LANXESS AG)       Polyvinylpyrrolidone K-90 Hydrogel   —   50   50   20   30   40       (available from Brainerd Chemical       Company, Inc., Tulsa, OK 74106)       Thiuram D dithiocarbamate   —   —   1.7   1.7   1.7   1.7       Carbon Black Reinforcement   —   —   50   50   50   50       Vulcanization Time @ 151° C.   20′   40′   40′   40′   40′   40′            Tested Properties            Approx. Strength, MPa   9.9   4.2   11   17   14.3   11.9       Relative elongation, %   535   500   240   320   290   260       Residual elongation, %   14   26   15   10   14   12       Shore A Hardness (Shore A units)   51   71   90   80   83   85       Change of % mass after swelling in   0.1   22.1   40.5   14.1   22.7   28.0       water at 90° C. for 10 days                  
 
       EXAMPLES 12-16  
       [0041]     In Situ Polymerized Hydrogel  
                                                                                                                   Ingredients   Ex. 12   Ex. 13   Ex. 14   Ex. 15   Ex. 16                                All ingredient amounts are given in parts by weight:            Therban ® 3446 (HNBR)   100   100   100   100   100       (hydrogenated acrylonitrile-butadiene       rubber available from LANXESS AG)       Perkadox ® Catalyst   8   8   8   8   8       Copolymer of maleinate oligomers and   30   15   20   30   20       allyl maleate oligomers       OP-10 surfactant   —   —   —   2   2       Carbon Black Reinforcement   50   50   50   50   50       Vulcanization Time @ 151° C.   50′   50′   50′   50′   50′            Tested Properties            Approx. Strength, MPa   19.7   23.2   23.6   18.4   23       Relative elongation, %   430   340   430   420   390       Residual elongation, %   17   10   15   18   14       Shore A Hardness (Shore A units)   53   62   58   53   60       Change of % mass after swelling in   40.9   9.3   17.6   33.0   20.6       water at 90° C. for 10 days                  
 
         [0042]     The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below.