Self-suspending proppants for hydraulic fracturing

Abstract

The invention provides for modified proppants, comprising a proppant particle and a hydrogel coating, wherein the hydrogel coating localizes on the surface of the proppant particle to produce the modified proppant, methods of manufacturing such proppants and methods of use.

1 - 73 . (canceled) 
     
     
         74 . A modified proppant comprising a proppant particle substrate and a durable hydrogel coating localized on the surface of the proppant particle substrate, wherein the hydrogel coating comprises a water-swellable polymer which is selected so that the modified proppant undergoes a volumetric expansion of at least 100% upon hydration in an excess of water. 
     
     
         75 . The modified proppant of  claim 74 , wherein the modified proppant undergoes a volumetric expansion of at least 500% upon hydration in an excess of water. 
     
     
         76 . The modified proppant of  claim 75 , wherein the shearing ratio of the proppant as determined by the Shear Analytical Test described in the specification is ? 0.6. 
     
     
         77 . The modified proppant of  claim 76 , wherein the water-swellable polymer has a weight average molecular weight of>about 5 million g/mol. 
     
     
         78 . The modified proppant of  claim 77 , wherein the hydrogel coating comprises a polymer selected from the group consisting of polyacrylamide, hydrolyzed polyacrylamide, copolymers of acrylamide with ethylenically unsaturated ionic comonomers, copolymers of acrylamide and acrylic acid salts, poly(acrylic acid) or salts thereof, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, guar gum, carboxymethyl guar, carboxymethyl hydroxypropyl guar gum, hydrophobically associating swellable emulsion polymers, and latex polymers. 
     
     
         79 . The modified proppant of  claim 78 , wherein the modified proppant is made by an invert emulsion coating technique in which the proppant particle substrate is combined with an invert emulsion in which the oil phase forms the continuous phase of the emulsion and a solution or dispersion of the hydrogel polymer in water forms the discontinuous, emulsified phase. 
     
     
         80 . The modified proppant of  claim 79 , wherein the modified proppant further comprises an alcohol selected from the group consisting of ethylene glycol, propylene glycol, glycerol, propanol, and ethanol. 
     
     
         81 . The modified proppant of  claim 80 , wherein the hydrogel polymer is an anionic polymer of acrylamide. 
     
     
         82 . The modified proppant of  claim 79 , wherein the hydrogel polymer is an anionic polymer of acrylamide. 
     
     
         83 . The modified proppant of  claim 77 , wherein the proppant is free-flowing. 
     
     
         84 . The modified proppant of  claim 75 , wherein the proppant is free-flowing. 
     
     
         85 . The modified proppant of  claim 74 , wherein the proppant is free-flowing. 
     
     
         86 . The modified proppant of  claim 74 , further comprising an oxidative breaker or an enzymatic breaker. 
     
     
         87 . The modified proppant of  claim 74 , further comprising a hydrophobic outer layer selected from the group consisting of fatty acids, aliphatic amines, hydrophobic quaternary amines, aliphatic amides, hydrogenated oils, vegetable oils, castor oil, triacetin, waxes, polyethylene oxides, and polypropylene oxides. 
     
     
         88 . The modified proppant of  claim 74 , further comprising a delayed hydration additive selected from the group consisting of a low hydrophilic-lipophilic balance surfactant, an exclusion agent capable of excluding a finishing surfactant, an ionic crosslinking agent, a covalent crosslinking agent and a monovalent salt charge shielder. 
     
     
         89 . The modified proppant of  claim 74 , further comprising an alcohol selected from the group consisting of ethylene glycol, propylene glycol, glycerol, propanol, and ethanol. 
     
     
         90 . The modified proppant of  claim 74 , further comprising an anticaking agent. 
     
     
         91 . The modified proppant of  claim 90 , wherein the anticaking agent is selected from the group consisting of a hydrophobic layer material, a finely divided particulate material and a crosslinking agent. 
     
     
         92 . The modified proppant of  claim 91 , wherein the anticaking agent is selected from the group consisting of calcium silicate, calcium carbonate, talc, kaolin, bentonite, diatomaceous earth, fumed silica, colloidal silica, microcrystalline cellulose and attapulgate. 
     
     
         93 . The modified proppant of  claim 74 , wherein the hydrogel coating includes a chemical additive comprising a tracer. 
     
     
         94 . A hydraulic fracturing formulation comprising water and the modified proppant of  claim 74 . 
     
     
         95 . The hydraulic fracturing formulation of  claim 94 , further comprising an oxidative breaker or an enzymatic breaker, 
     
     
         96 . The hydraulic fracturing formulation of  claim 94 , wherein the hydraulic fracturing formulation further comprises a thickening agent to reduce the rate at which the modified proppant settles in the fracturing formulation, and further wherein the amount of this thickening agent is less than would otherwise be necessary to achieve the same rate of proppant settling in an otherwise identical control aqueous fracturing formulation made with an uncoated proppant. 
     
     
         97 . In a process for fracturing a geological formation penetrated by a well in which an aqueous fracing fluid containing a proppant is charged into the geological formation with pulsed pressure, a method for reducing the amount of thickening agent that is added to the fracing fluid comprising selecting as the proppant the modified proppant of  claim 74 . 
     
     
         98 . The method of  claim 97 , wherein the modified proppant hydrates essentially completely within 2 hours of first being combined with the aqueous fracing fluid. 
     
     
         99 . The method of  claim 98 , wherein the modified proppant hydrates essentially completely within 10 minutes of first being combined with the fracing fluid. 
     
     
         100 . A modified proppant comprising a proppant particle substrate and a hydrogel polymer coating which localizes on the surfaces of the proppant particle substrate thereby producing the modified proppant, wherein hydrogel polymer is selected and applied so that when the modified proppant is exposed to water in a manner which allows its hydrogel polymer coating to hydrate essentially completely, the hydrogel coating that is produced
 (i) is durable, and   (ii) causes the volume the modified proppant to expand by a factor of at least 5 as compared to the modified proppant when dry, as determined by the Settled Bed Height Analytical Test described in the specification.   
     
     
         101 . The modified proppant of  claim 100 , wherein hydrogel polymer is selected so that when the modified proppant is dry, it is free flowing. 
     
     
         102 . The modified proppant of  claim 101 , wherein the modified proppant is dry. 
     
     
         103 . The modified proppant of  claim 100 , wherein the hydrogel is selected so that, after 1 gram of the modified proppant is mixed with tap water in a 20 ml glass vial and allowed to sit undisturbed for 30 minutes, the modified proppant exhibits a settled bed height which is about 7 (5.8/0.8) about 28 (22.6/0.8) times greater than the settled bed height of an otherwise identical proppant not modified with a hydrogel coating. 
     
     
         104 . The modified proppant of  claim 103 , wherein the shearing ratio of the modified proppant as determined by the Shear Analytical Test described in the specification is ≧0.6. 
     
     
         105 . The modified proppant of  claim 104 , wherein the weight average molecular weight of the hydrogel polymer is ≧5 million Daltons. 
     
     
         106 . The modified proppant of  claim 104 , wherein the hydrogel polymer coating is made from a hydrogel polymer which hydrates essentially completely within 2 hours of being contacted with an excess of tap water at 20° C. 
     
     
         107 . The modified proppant of  claim 104 , wherein the hydrogel polymer hydrates essentially completely within 30 minutes of first being combined with the fracing fluid. 
     
     
         108 . The modified proppant of  claim 74 , wherein the hydrogel coating comprises a polymer selected from the group consisting of polyacrylamide, hydrolyzed polyacrylamide, copolymers of acrylamide with ethylenically unsaturated ionic comonomers, copolymers of acrylamide and acrylic acid salts, poly(acrylic acid) or salts thereof, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, guar gum, carboxymethyl guar, carboxymethyl hydroxypropyl guar gum, hydrophobically associating swellable emulsion polymers, and latex polymers. 
     
     
         109 . The modified proppant of  claim 109 , wherein the modified proppant is made by an invert emulsion coating technique in which the proppant particle substrate is combined with an invert emulsion in which the oil phase forms the continuous phase of the emulsion and a solution or dispersion of the hydrogel polymer in water forms the discontinuous, emulsified phase. 
     
     
         110 . The modified proppant of  claim 109 , wherein the modified proppant further comprises an alcohol selected from the group consisting of ethylene glycol, propylene glycol, glycerol, propanol, and ethanol. 
     
     
         111 . The modified proppant of  claim 110 , wherein the hydrogel polymer is an anionic polymer of acrylamide. 
     
     
         112 . In a process for fracturing a geological formation penetrated by a well in which a fracing fluid containing a proppant is charged into the geological formation with pulsed pressure, a method for reducing the amount of thickening agent that is added to the fracing fluid comprising selecting as the proppant the modified proppant of  claim 100 . 
     
     
         113 . A modified proppant comprising a proppant particle substrate and a hydrogel coating, wherein the hydrogel coating localizes on the surfaces of the proppant particle substrate to produce the modified proppant, and further wherein the hydrogel coating includes a sufficient amount of an anticaking agent so that the modified proppant is free-flowing after being subjected to a relative humidity of 80%-90% for one hour at 25-35° C. 
     
     
         114 . The modified proppant of  claim 113 , wherein the anticaking agent is selected from the group consisting of calcium silicate, calcium carbonate, talc, kaolin, bentonite, diatomaceous earth , silica, colloidal silica, microcrystalline cellulose and attapulgate.