Hydraulic fracture composition and method

Abstract

A method for improving the performance of fracturing processes in oil production fields may rely on polymer coated particles carried in the fracturing fluid. The particles may include heavy substrates, such as sand, ceramic sand, or the like coated with polymers selected to absorb water, increasing the area and volume to travel more readily with the flow of fluid without settling out, or allowing the substrate to settle out. Ultimately, the substrate may become lodged in the fissures formed by the pressure or hydraulic fracturing, resulting in propping open of the fissures for improved productivity.

What is claimed is: 
     
         1 . A method for making self-suspending proppant particles, the method comprising:
 mixing substrate particles with a liquid binder so that at least a portion of the substrate particles are at least partly coated with the liquid binder;   applying one or more water-absorbing polymers to the at least a portion of the substrate particles that are at least partly coated with liquid binder to form polymer-coated substrate particles, wherein the applying one or more water-absorbing polymers includes applying a first water-absorbing polymer in a first form, and applying a second water-absorbing polymer in a second form that is different from the first form, wherein the first and second forms are selected from a powder and an emulsion, and wherein each of the first and second water-absorbing polymers is about 20 mol. % anionic to about 50 mo. % anionic; and   exposing the polymer-coated substrate particles to heat sufficient to cause crosslinking in at least a portion of the one or more water-absorbing polymers present on the polymer coated substrate particles, thereby forming self-suspending proppant particles.   
     
     
         2 . The method according to  claim 1 , wherein the first water-absorbing polymer comprises a first co-polymer of acrylate monomers and acrylamide monomers, wherein the first form of the first water-absorbing polymer is the powder form. 
     
     
         3 . The method according to  claim 2 , wherein the second water-absorbing polymer comprises a second co-polymer of acrylate monomers and acrylamide monomers, wherein the second form of the second water-absorbing polymer is the emulsion, wherein the emulsion is a water-in-oil emulsion, wherein, in the water-in-oil emulsion, the second water-absorbing polymer is in an aqueous phase that is dispersed in an oil phase. 
     
     
         4 . The method according to  claim 1 , a molecular weight of the first water-absorbing polymer is less than a molecular weight of the second water-absorbing polymer. 
     
     
         5 . The method according to  claim 4 , wherein the molecular weight of the first water-absorbing polymer is at least about 1 Million Daltons (g/mol) less than the molecular weight of the second water-absorbing polymer. 
     
     
         6 . The method according to  claim 1 , wherein the first and second water-absorbing polymers are linear prior to the applying heat to the polymer-coated substrate particles. 
     
     
         7 . The method according to  claim 1 , wherein each of the first and second water-absorbing polymers is at least about 30 mol. % anionic to about 40 mol. % anionic. 
     
     
         8 . The method according to  claim 2 , wherein the powder comprises powder particles with a maximum dimension of from about 50 microns to about about 300 microns. 
     
     
         9 . The method according to  claim 1 , wherein the liquid binder comprises glycerol. 
     
     
         10 . The method according to  claim 9 , wherein the glycerol is present in the self-suspending proppant particles. 
     
     
         11 . The method according to  claim 3 , wherein the applying one or more water-absorbing polymers to the at least a portion of the substrate particles comprises applying the first water-absorbing polymer in the first form prior to applying the second water-absorbing polymer in the second form. 
     
     
         12 . The method according to  claim 3 , wherein the applying one or more water-absorbing polymers to the at least a portion of the substrate particles comprises applying the second water-absorbing polymer in the second form prior to applying the first water-absorbing polymer in the first form. 
     
     
         13 . The method according to  claim 1 , wherein the exposing the polymer-coated substrate particles to heat comprises exposing the polymer-coated substrate particles to a temperature of less than about 200° F. (93° C.). 
     
     
         14 . The method according to  claim 1 , further comprising adding a flowing agent to the self-suspending proppant particles. 
     
     
         15 . The method according to  claim 14 , wherein the flowing agent comprises a sodium aluminosilicate. 
     
     
         16 . The method according to  claim 1 , wherein the self-suspending proppant particles are configured to remain suspended in a 1000 ppm CaCO 3  aqueous solution for at least 30 minutes at a temperature of 170° F. 
     
     
         17 . A method for making self-suspending proppant particles, the method comprising:
 adding a volume of substrate particles to a mixing vessel, the substrate particles comprising sand;   coating at least a portion of the substrate particles with glycerol in the mixing vessel to form binder-coated substrate particles,   mixing a first water-absorbing polymer with the binder-coated substrate particles in the mixing vessel, the first water-absorbing polymer comprising a co-polymer of acrylamide monomers and acrylate monomers, wherein the first water-absorbing polymer is about 20 mol. % anionic to about 50 mo. % anionic, and wherein the first water-absorbing polymer is in powdered form;   subsequent to mixing the first water-absorbing polymer with the binder-coated substrate particles, mixing a second water-absorbing polymer with first water-absorbing polymer and the binder-coated substrate particles to form polymer-coated substrate particles, the second water-absorbing polymer comprising a co-polymer of acrylamide monomers and acrylate monomers, wherein the second water-absorbing polymer is about 20 mol. % anionic to about 50 mo. % anionic, wherein the second water-absorbing polymer is present in a water-in-oil emulsion, and wherein each of the polymer-coated substrate particles comprises a polymeric coating that includes the first water-absorbing polymer and the second water-absorbing polymer; and   exposing the polymer-coated substrate particles to heat sufficient to cause crosslinking in the polymeric coating present on the polymer-coated substrate particles, thereby forming self-suspending proppant particles.   
     
     
         18 . The method according to  claim 17 , wherein each of the first and second water-absorbing polymers are linear polymers prior to the exposing the polymer-coated substrate particles to heat. 
     
     
         19 . The method according to  claim 17 , wherein the self-suspending proppant particles are configured to remain suspended in a 1000 ppm CaCO 3  aqueous solution for at least 30 minutes at a temperature of 170° F. 
     
     
         20 . Self-suspending proppant particles, comprising:
 substrate particles, the substrate particles comprising sand; and   an outer polymeric coating positioned on an outer surface of each of the substrate particles, the outer polymeric coating comprising first and second water-absorbing polymers that are at least partly covalently crosslinked, wherein each of the first and second water-absorbing polymers comprise a co-polymer of acrylate monomers and acrylamide monomers, wherein a molecular weight of the first water-absorbing polymer is at least about 1 Million Daltons (g/mol) greater than a molecular weight of the second water-absorbing polymer, wherein each of the first and second water-absorbing polymers is about 20 mol. % to about 50 mol. % anionic, wherein the first water-absorbing polymer was applied to the substrate particles in the form of an emulsion, and wherein the second water-absorbing polymer was applied to the substrate particles in powdered form,   wherein the self-suspending proppant particles remain suspended in a 1000 ppm CaCO 3  aqueous solution for at least 30 minutes at a temperature of 170° F.