Methods for using high strngth ceramic elements

Abstract

One embodiment of the present invention relates to spherical ceramic elements, such as proppants, for maintaining permeability in subterranean formations to facilitate extraction of oil and gas therefrom. The strength of the ceramic element may be enhanced by combining materials having different coefficients of thermal expansion. Methods of making the ceramic elements are also disclosed.

1 - 23 . (canceled) 
     
     
         24 . A method for propping a geological formation, comprising the steps of: mixing a plurality of proppants with a liquid to form a flowable mixture and forcing the mixture under pressure into the geological formation until at least a portion of the proppants are disposed into cracks in the formation, wherein at least 5 weight percent of said proppants each comprises a sintered base secured to a sintered layer and said base exerts a compressive force on said layer. 
     
     
         25 . The method of  claim 24  wherein said base exerts a compressive force on said layer prior to and after mixing the proppants with the liquid. 
     
     
         26 . The method of  claim 24  wherein said geological formation elevates the temperature of said proppants above 50° C., said increase in temperature causes said base to exert a compressive force on said layer. 
     
     
         27 . The method of  claim 26  wherein said base has a coefficient of thermal expansion and said layer has a coefficient of thermal expansion that exceeds said base's coefficient of thermal expansion. 
     
     
         28 . The method of  claim 24  wherein at least 50 weight percent of said proppants each comprises a sintered base secured to a sintered layer and said base exerts a compressive force on said layer. 
     
     
         29 . The method of  claim 28  wherein at least 90 weight percent of said proppants each comprises a sintered base secured to a sintered layer and said base exerts a compressive force on said layer. 
     
     
         30 . A method for propping the fissures in a geological formation, said method comprising the steps of:
 (a) mixing a plurality of proppants with a liquid to form a flowable mixture, wherein said proppants comprise a sintered base bonded to a sintered layer, said base exerting an initial force on said layer;   (b) disposing the mixture under pressure into the geological formation until at least a portion of the proppants are inserted into the fissures in the formation; and   (c) utilizing geothermal heat supplied by said geological formation to heat said proppants, wherein said heat causes the exertion of a net compressive force on said layer, said net compressive force exceeding said initial force.   
     
     
         31 . The method of  claim 30  wherein, for a given proppant, said layer has a coefficient of thermal expansion, said base has a coefficient of thermal expansion, and said layer's coefficient of thermal expansion exceeds said base's coefficient of thermal expansion. 
     
     
         32 . The method of  claim 31  wherein said layer's coefficient of thermal expansion exceeds said base's coefficient of thermal expansion by at least 10% of the base's coefficient of thermal expansion. 
     
     
         33 . The method of  claim 30  wherein said geothermal heat increases the temperature of said proppant above 50° C. 
     
     
         34 - 41 . (canceled)