Coated Proppants
AssigneeDow Global Technologies LLC
InventorPraveen Agarwal
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Abstract
Coated proppant particles are prepared by coating the particles with a coating composition that includes at least one polyisocyanate and at least one ingredient selected from i) an isocyanate trimerization catalyst, ii) a carbodiimide catalyst, iii) an alcohol, iv) a polyamine and v) an alkanolamine, and curing the coating composition. Starch is present during at least part of the curing step, such that the starch becomes embedded in at least a portion of the cured coating. The coating composition cures rapidly at moderate temperatures, and bonds to itself well under conditions of heat and pressure as are experienced by the particles in subterranean formations.
Claims15
A method for forming a coated proppant, comprising applying a coating composition to the surface of solid substrate particles, wherein the solid substrate particles are thermally stable to a temperature of at least 150° C., wherein the coating composition comprises at least one polyisocyanate and at least one additional ingredient selected from i) an isocyanate trimerization catalyst, ii) a carbodiimide catalyst, iii) an alcohol, iv) a polyamine and v) an alkanolamine, and curing the coating composition at an elevated temperature of to up to 150° C. and for a period of up to 10 minutes on the surface of the substrate particles to form the solid polymeric coating at the surface of the solid substrate particles, wherein starch is present during at least a portion of said curing step such that starch becomes incorporated into the solid polymeric coating.
The method of any preceding claim wherein the coating composition is applied to the surface of the substrate particles and partially cured, an adhesion promoter is thereafter applied to the coated particles, starch is applied to the coating particles after the adhesion promoter is applied, and the curing of the coating composition is thereafter completed.
The method of any preceding claim, wherein the coating composition is sprayed onto the substrate particles.
The method of any preceding claim wherein the coating composition is cured at a temperature of 80 to 150° C.
The method of any preceding claim wherein the amount of the coating composition applied to the surface of the substrate particles is sufficient to provide 0.1 to 10 parts by weight of polyisocyanate per 100 parts by weight substrate particles.
The method of any preceding claim wherein the polyisocyanate is a polymeric MDI and the coating composition comprises at least one isocyanate trimerization catalyst.
The method of any preceding claim wherein the substrate particles are sand.
The method of any preceding claim wherein the substrate particles are coated continuously by first washing and then drying the particles at a first predetermined elevated temperature, cooling the washed particles to a second, lower predetermined temperature, then feeding the particles without further heating into an inlet of a combined continuous mixer and conveyor unit, feeding the coating composition and starch into the combined continuous mixer and conveyor unit, mixing the coating composition and starch with the substrate particles, conveying the coated particles through the combined continuous mixer and conveyor unit wherein the coating composition is cured by transfer of heat from the particles, and discharging the coated particles from an outlet of the combined continuous mixer and conveyor unit.
A coated proppant particle made in the method of any preceding claim.
A coated proppant particle comprising a substrate particle having a polymeric coating that weighs 0.1 to 10 weight percent of the weight of the substrate particle, wherein the polymeric coating contains one or more of isocyanurate, carbodiimide, urea and urethane linkages and starch is incorporated into the polymeric coating.
Dependencies are inferred from the claim text.