Patent Publication Number: US-2012031612-A1

Title: Swellable Elastomer for Water Shut Off in Gravel Pack

Description:
TECHNICAL FIELD 
     The present invention relates to the field of downhole tools, and in particular to gravel pack completions. 
     BACKGROUND ART 
     Gravel packing is a method of well completion in which a slotted or perforated liner is placed in a well and surrounded with a gravel mixture. Gravel packing is most commonly used in the open hole wells, but may also be used in cased wells. The mass of gravel in the gravel pack excludes sand from the wellbore, while allowing continued production. 
     SUMMARY OF INVENTION 
     By mixing granules of swellable elastomer into the gravel pack, fluid breakthroughs can be restricted or eliminated in a self-actuated self-healing gravel pack completion. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate an implementation of apparatus and methods consistent with the present invention and, together with the detailed description, serve to explain advantages and principles consistent with the invention. In the drawings, 
         FIG. 1  is a cutaway view illustrating a gravel pack completion according to the prior art with a fluid breakthrough. 
         FIG. 2  is a cutaway view illustrating a gravel pack completion according to one embodiment. 
         FIG. 3  is a cutaway view illustrating a self-actuated closure of a fluid breakthrough achieved by the embodiment of  FIG. 2 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the invention. It will be apparent, however, to one skilled in the art that the invention may be practiced without these specific details. In other instances, structure and devices are shown in block diagram form in order to avoid obscuring the invention. References to numbers without subscripts or suffixes are understood to reference all instance of subscripts and suffixes corresponding to the referenced number. Moreover, the language used in this disclosure has been principally selected for readability and instructional purposes, and may not have been selected to delineate or circumscribe the inventive subject matter, resort to the claims being necessary to determine such inventive subject matter. Reference in the specification to “one embodiment” or to “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiments is included in at least one embodiment of the invention, and multiple references to “one embodiment” or “an embodiment” should not be understood as necessarily all referring to the same embodiment. 
     One problem with gravel pack completions has been fluid breakthroughs from the surrounding strata.  FIG. 1  is a cutaway view of a typical gravel-packed completion according to the prior art. A tubular  130  is inserted into the open hole well, with slots  135  allowing fluid passage in the annulus between the tubular  130  and the open hole rock or sands  100 . A gravel pack  120  is inserted in the annulus between the tubular  130  and the open hole. 
     When a crack or fissure  140  occurs in the surrounding open hole  100 , water or other fluids may leak into the annulus, flowing through the gravel pack  120  an end to the poor of the tubular  130  through slots  135 , as illustrated in area  145  in  FIG. 1 . Such a fluid breakthrough can be difficult to shut off. In conventional gravel pack completions, packers between zones and the water shut off sleeves that require intervention to close have been used to shut off fluid breakthroughs. 
       FIG. 2  illustrates an improved gravel pack completion technique using a gravel pack  200  according to one embodiment that may eliminate or reduce the problem illustrated in  FIG. 1 . In addition to conventional gravel, the improved gravel pack  200  includes a predetermined amount of a swellable elastomer performed as granules that are mixed into the gravel pack. During normal operation after the gravel packing, the improved gravel pack  200  operates just as the conventional gravel pack  120 , with the gravel and elastomer mixture excluding sand from traversing the slots  135  and entering the bore of the tubular  130 . 
     As illustrated in  FIG. 3 , however, when a water or other fluid breakthrough occurs through fissure  140 , the swellable elastomer granules in area  300  swellable in the presence of a fluid and at least partially restrict or shuts off the flow of fluid into the tubular. This creates an autonomous self-actuated fluid shut off in the improved gravel pack  200  itself 
     Only the area  300  of the gravel pack  200  that is in contact with the triggering fluid actuates, thus other portions of the gravel pack  200  may continue to function normally. Because swellable material such as are selected for the improved gravel pack  200  remain swollen once they have been exposed to their triggering fluid, the shut off is long lasting and may indeed be permanent. 
     Many gravel pack wells are in areas where the open hole breakthrough would be a water breakthrough, thus in one embodiment, the swellable elastomer granules are formed of a material selected to swell when exposed to water, such as a nitrile, or a nitrile mixed with a super absorbent polymer. In other embodiments, where the fluid may be a hydrocarbon fluid, or a mixture of water and hydrocarbons, the elastomer granules may be formed of an ethylene propylene diene monomer (EPDM) or a mixture of nitrile and EPDM granules. 
     The granules may be formed as irregular chunks of the swellable elastomer, or in any desired 3-dimensional configuration. The granules may be sized in multiple sizes, and in one embodiment may be sized to correspond to the average particle size of the gravel in the gravel pack  200 . In other embodiments, the swellable elastomer particles are sized to be smaller than the average gravel particle size. 
     The swellable elastomer is preferably evenly mixed with the gravel. In one embodiment, the gravel-elastomer mixture may be mixed on-site. In other embodiments, the gravel and elastomer particles may be premixed off-site. 
     The desired relative percentage of gravel to elastomer particles may vary for different applications, but in most embodiments, the elastomeric granules may comprise at least 25% by volume of the gravel-elastomer mixture. 
     It is to be understood that the above description is intended to be illustrative, and not restrictive. For example, the above-described embodiments may be used in combination with each other. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention therefore should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein.”