Functionally graded swellable packers

Abstract

A swellable packer including a tubular member and a swellable element. The tubular member is disposable on a mandrel configured to be deployed into a wellbore. The swellable element is disposed around the tubular member, and has segments of different cross link densities, with the segments configured to provide a varying cross link density in the swelleable element along a thickness of the swellable element, an azimuth of the swellable element, or both.

1 . A swellable packer, comprising:
 a tubular member configured to be deployed into a wellbore; and   a swellable element disposed around the tubular member and having segments with different segment cross link densities, the segments configured to provide a cross link density in the swelleable element that varies along a thickness of the swellable element, an azimuth of the swellable element, or both.   
     
     
         2 . The swellable packer of  claim 1 , wherein the cross link density of the swellable element increases from an inner diameter of the swellable element to an outer diameter of the swellable element. 
     
     
         3 . The swellable packer of  claim 1 , wherein the cross link density of the swellable element varies as a linear function. 
     
     
         4 . The swellable packer of  claim 1 , wherein the cross link density of the swellable element varies as a nonlinear function. 
     
     
         5 . The swellable packer of  claim 1 , wherein the cross link density of the swellable element varies chaotically. 
     
     
         6 . The swellable packer of  claim 1 , wherein the swellable element comprises a first segment having a first segment cross link density and a second segment having a second segment cross link density that is greater than the first segment cross link density. 
     
     
         7 . A method of making a swellable packer, comprising:
 wrapping a sheet of uncured elastomeric material around a mandrel;   curing the sheet of uncured elastomeric material to form a swellable packer comprising a swellable element; and   varying the cross link density along a thickness of the swellable element, along an azimuth of the swellable element, or both.   
     
     
         8 . The method of  claim 7 , wherein varying the cross link density comprises providing transient thermal energy to the sheet during curing. 
     
     
         9 . The method of  claim 8 , wherein providing the transient thermal energy comprises:
 heating the sheet in heating intervals of from about 1 to about 2 minutes; and   cooling the sheet between the heating intervals for a time period from about 5 minutes to about 20 minutes.   
     
     
         10 . The method of  claim 7 , wherein varying the cross link density comprises varying the composition of a cross linking agent disposed on the sheet. 
     
     
         11 . The method of  claim 7 , wherein varying the cross link density comprises varying a concentration of a cross linking agent disposed on the sheet. 
     
     
         12 . The method of  claim 7 , wherein varying the cross link density comprises increasing the cross link density from an inner diameter of the swellable packer to an outer diameter of the swellable element. 
     
     
         13 . The method of  claim 7 , further comprising blending the uncured elastomeric material with granules of a cross linking agent, wherein varying the cross link density comprises varying the cross link density as a function of distance from the granules. 
     
     
         14 . The method of  claim 13 , wherein varying the cross link density further comprises varying a thickness of shells encapsulating the granules to vary a release profile of the granules during curing. 
     
     
         15 . The method of  claim 13 , wherein varying the cross link density further comprises varying a coating material of shells encapsulating the granules to vary a release profile of the granules during curing. 
     
     
         16 . A method of sealing an annulus of a wellbore, comprising:
 disposing a swellable packer in the wellbore, the swellable packer having a swellable element with a varying cross link density along a thickness of the swellable element, an azimuth of the swellable element, or both;   exposing the swellable element to a downhole trigger; and   swelling the swellable element into irregularities of the wellbore to provide a hermetic seal with the wellbore.   
     
     
         17 . The method of  claim 16 , wherein the varying cross link density increases from an inner diameter of the swellable element to an outer diameter of the swellable element. 
     
     
         18 . The method of  claim 16 , wherein the cross link density varies as a linear function. 
     
     
         19 . The method of  claim 16 , wherein the cross link density varies as a nonlinear function. 
     
     
         20 . The method of  claim 19 , wherein the cross link density varies randomly.