Coated And Cured Proppants

Abstract

Solid proppants are coated with a coating that exhibits the handling characteristics of a precured coating while also exhibiting the ability to form particle-to-particle bonds at the elevated temperatures and pressures within a wellbore. The coating includes a substantially homogeneous mixture of (i) at least one isocyanate component having at least 2 isocyanate groups, and (ii) a curing agent. The coating process can be performed with short cycle times, e.g., less than about 4 minutes, and still produce a dry, free-flowing, coated proppant that exhibits low dust characteristics during pneumatic handling but also proppant consolidation downhole for reduced washout and good conductivity.

1 - 33 . (canceled) 
     
     
         34 . A coated, discrete, free-flowing, proppant solids comprising solid proppant core particles that are substantially covered with a substantially cured coating that comprises:
 (a) at least one isocyanate component;   (b) a hydroxy-functional polyether polyol;   (c) a different polyol other than said hydroxy-functional polyether; and   (d) at least one tin complex catalyst;   wherein said coating forms particle-to-particle bonds under downhole conditions that exhibit an unconfined compressive strength of greater than 100 psi, that resists proppant flowback at elevated temperature and pressure, and that further exhibits a negative TMA slope within the range of about 125° C. and 175° C., wherein said coated proppants exhibit a loss of coating of less than 15 wt % when tested according to ISO 13503-5:2006(E).   
     
     
         35 . The coated, discrete, free-flowing, proppant solids of  claim 34 , wherein the tin catalyst is stannous 2-ethylhexanoate. 
     
     
         36 . The coated, discrete, free-flowing, proppant solids of  claim 34 , wherein the cured coating further comprises a silane. 
     
     
         37 . The coated, discrete, free-flowing, proppant solids of  claim 34 , wherein the coated solids comprises an inner layer in contact with the solid proppant core particles, wherein the inner layer is an adhesion agent. 
     
     
         38 . The coated, discrete, free-flowing, proppant solids of  claim 36 , wherein the adhesion agent is a silane. 
     
     
         39 . A method of preparing the coated, discrete, free-flowing, proppant solids of  claim 34 , the method comprising:
 contacting the solid proppant core particles with the at least one isocyanate component;   the hydroxy-functional polyether polyol; and the different polyol other than said hydroxy-functional polyether in the presence of at least one tin complex catalyst.   
     
     
         40 . The method of  claim 39 , further comprising contacting the solid proppant core particles with a silane. 
     
     
         41 . A coated core particle that is substantially covered with:
 an adhesion agent coupled to the particle, wherein the adhesion agent comprises a silane; and   a substantially cured coating coupled to the adhesion agent, wherein the substantially cured coating is formed from a mixture that comprises at least one isocyanate component, a hydroxy-functional polyether polyol, and at least one tin complex catalyst.   
     
     
         42 . The coated core particle of  claim 41 , wherein said coating can form particle-to-particle bonds that exhibit an unconfined compressive strength sufficient to generate proppant consolidation and provide flowback control. 
     
     
         43 . The coated core particle of  claim 41 , wherein said coating can form coated particle-to-coated particle bonds under downhole conditions that exhibit an unconfined compressive strength of greater than 100 psi. 
     
     
         44 . The coated core particle of  claim 41 , wherein the coated core particle exhibits a negative TMA slope within the range of about 125° C. and 175° C. 
     
     
         45 . The coated core particle of  claim 41 , wherein said coated core particle exhibits a loss of coating of less than 15 wt % when tested according to ISO 13503-5:2006(E). 
     
     
         46 . The coated, discrete, free-flowing, proppant solids of  claim 34 , wherein the core particle is a ceramic core particle. 
     
     
         47 . The coated, discrete, free-flowing, proppant solids of  claim 34 , wherein the core particle is a sand particle. 
     
     
         48 . The coated, discrete, free-flowing, proppant solids of  claim 34 , wherein the coating further comprises a pigment, dye, or tint. 
     
     
         49 . The coated, discrete, free-flowing, proppant solids of  claim 34 , wherein the coating further comprises mica.