Swellable ball sealers

Abstract

Swellable ball sealers comprising swellable material are described. A swellable ball sealer may be used as a diversion agent by being suspended in a fluid injected into a wellbore and swelling once seated on a perforation such that the swellable ball sealer adapts to the shape of a perforation opening on which the swellable ball sealer has seated.

What is claimed is: 
     
         1 . A ball sealer for plugging perforations in a wellbore, the ball sealer comprising:
 a swellable material configured to expand and produce a seal between an outer surface of a ball sealer and a surface of the perforation; and   wherein the swellable material conforms to a geometry of the perforation during swelling to produce the seal.   
     
     
         2 . The ball sealer of  claim 1 , wherein the swellable material swells upon exposure to downhole fluids. 
     
     
         3 . The ball sealer of  claim 1 , wherein an initial diameter of the ball sealer is less than a diameter of the perforation. 
     
     
         4 . The ball sealer of  claim 1 , wherein the swellable material degrades in response to conditions in the wellbore. 
     
     
         5 . The ball sealer of  claim 1 , wherein the swellable material degrades in response to contact with a particular fluid in the wellbore. 
     
     
         6 . The ball sealer of  claim 1 , further comprising a semipermeable coating, surrounding the swellable material. 
     
     
         7 . The ball sealer of  claim 1 , further comprising a degradable coating, surrounding the swellable material. 
     
     
         8 . The ball sealer of  claim 1 , further comprising an inner rigid core surrounded by an outer layer of the swellable material. 
     
     
         9 . The ball sealer of  claim 1 , wherein the swellable material is a swellable polymer or a swellable elastomer or both. 
     
     
         10 . The ball sealer of  claim 9 , wherein the swellable elastomer comprises an oil swellable elastomer. 
     
     
         11 . The ball sealer of  claim 1 , wherein the swellable material comprises a water-swellable material. 
     
     
         12 . A method of sealing a perforation in a wellbore comprising:
 injecting into the wellbore a ball sealer suspended in a fluid to a region of the perforation, wherein the ball sealer comprises a swellable material;   applying pressure in the wellbore to seat the ball sealer on the perforation;   exposing the swellable material to a triggering fluid; and   allowing the ball sealer to swell and produce a seal between an outer surface of the seated ball sealer and a surface of perforation.   
     
     
         13 . The method of  claim 12 , wherein the swellable material is capable of swelling in oil and/or in water. 
     
     
         14 . The method of  claim 12 , further comprising:
 introducing ball sealers in the fluid in an amount sufficient to plug perforations in the wellbore adjacent to a first zone; and   applying pressure in an amount sufficient to fracture a formation in an area adjacent to the first zone which causes the ball sealers to seal off perforations in the first zone and direct the fluid into a second zone of the wellbore thereby fracturing the formation adjacent to the second zone.   
     
     
         15 . The method of  claim 12 , wherein the swellable material comprises a deformable swellable layer. 
     
     
         16 . A system for injecting fluids into a formation, the system comprising:
 a casing which includes a plurality of perforations;   a plurality of ball sealers which are pumped into the casing with a fluid, wherein the ball sealers comprise:   a layer of swellable material which is adapted to conform to a geometry of the perforation during swelling; and   forming a plug with one or a plurality of the ball sealers that inhibits fluid flow through the perforation.   
     
     
         17 . The system of  claim 16 , wherein the swellable material comprises an elastomer operable to swell upon exposure to a hydrocarbon fluid. 
     
     
         18 . The system of  claim 16 , wherein the swellable material is operable to increase in volume on exposure to a triggering fluid. 
     
     
         19 . The system of  claim 16 , wherein the swellable material comprises segments having different cross link densities. 
     
     
         20 . The system of  claim 16 , further comprising a multilayered swellable material comprising layers of swellable material wherein each layer has a different swelling characteristic.