Proppant Mixtures

Abstract

The invention relates to a propped, fractured, subterranean field with (a) a first proppant and (b) a second proppant that exhibits a relatively higher average crush strength and/or an ability to form a particle to particle bonded structure than the first proppant. Preferably, the first proppant is uncoated sand and the second proppant is resin-coated sand. The proppants can be deposited as a substantially homogeneous mixture or in layered structures (vertical or horizontal) within the fractured field. Deformation of the second proppant under closure stress acts to spread out the compression pressures in a mixture so as to reduce failure of the first proppant. Similar protective effects are found when the proppants are deposited in layers. When formed as vertical pillar structures, the second proppant structures can also act as in-situ screens that inhibit formation fines from migrating through the proppant pack to the detriment of field conductivity.

1 - 18 . (canceled) 
     
     
         19 . A method for forming a propped, subterranean, hydraulically-fractured field in an oil or gas well by steps that comprise:
 injecting into the fractured field a first volume of first proppant and a second volume of second proppant exhibiting a higher average crush strength relative to said first proppant,   wherein the first proppant is an uncoated proppant and the second proppant is a coated proppant,   wherein the injecting into the fractured field comprises injecting:   (i) a mixture of the first and second proppants; or   (ii) sequentially injecting the first volume of proppants and then injecting the second volume of proppants for at least two cycles of alternating injections to form a layered structure in of first proppants and second proppants within the fractured subterranean field.   
     
     
         20 . The method of  claim 19 , wherein the injection is performed simultaneously with a fracturing step or shortly thereafter. 
     
     
         21 . The method of  claim 19 , wherein the first proppant and the second proppant are substantially the same size. 
     
     
         22 . The method of  claim 19 , wherein the amount of the second proppant is about 10-30% and the amount of the first proppant is about 70-85%. 
     
     
         23 . The method of  claim 19 , wherein the layered structure is distant from a wellbore. 
     
     
         24 . The method of  claim 19 , wherein the coated proppant is a resin-coated proppant. 
     
     
         25 . The method of  claim 19 , wherein the uncoated proppant is uncoated sand. 
     
     
         26 . The method of  claim 19 , wherein the coated proppant is a coated sand. 
     
     
         27 . The method of  claim 19 , wherein the coated proppant is a polyurethane-coated proppant. 
     
     
         28 . The method of  claim 19 , wherein the coated proppant is a polyurea-coated proppant. 
     
     
         29 . The method of  claim 19 , wherein the coated proppant is coated with a phenolic resin. 
     
     
         30 . The method of  claim 19 , wherein the coated proppant is coated with an epoxy resin. 
     
     
         31 . The method of  claim 19 , wherein the coated proppant is coated with a phenolic resin and an epoxy resin. 
     
     
         32 . The method of  claim 19 , wherein said coated sand is coated with a polyurethane coating and a polyurea coating. 
     
     
         33 . The method of  claim 19 , wherein the first proppant is injected as a mixture with said second proppant. 
     
     
         34 . The method of  claim 19 , wherein the injecting step is performed with crosslinked frac fluid. 
     
     
         35 . The method of  claim 19 , wherein said first and second proppants are sequentially injected to form a series of horizontally-disposed proppant layer structures within a fracture. 
     
     
         36 . The method of  claim 19 , wherein the injecting step is performed with water or slick water frac fluid. 
     
     
         37 . A method for forming a propped, subterranean, hydraulically-fractured field in an oil or gas, the method comprising sequentially injecting a volume of first proppants and then injecting a volume of second proppants to form a layered structure of first proppants and second proppants within the fractured subterranean field,
 wherein the second proppant exhibits a higher average crush strength relative to said first proppant,   wherein the first proppant and the second proppant are substantially the same size,   wherein the first proppant is an uncoated proppant,   wherein the second proppant is a coated proppant.   
     
     
         38 . The method of  claim 37 , wherein the amount of the second proppant is about 10-30% and the amount of the first proppant is about 70-85%.