Materials Science Improves Silica Sand Strength

摘要

Due to its low cost, availability, roundness and strength, silica sand has been the preferred proppant for hydraulic fracturing. However in deeper completions stronger proppant must be used. If the strength of the material does not match the formation closure stress conditions, it will crush and fines will be generated, often leading to significant proppant pack conductivity damage. As formation closure stress increases, materials that can withstand stronger stresses than silica sand, such as resin- coated sands and ceramic proppants, must be used. Resin-coated silica proppant can be used up to about 8,000 psi closure stress, improving fracture treatment results; ceramics made of aluminosilicates ores are much stronger and provide better conductivity for formation closures of over 12,000 psi. However ceramic proppants cost significantly more than silica proppant and have higher densities that require higher fracturing fluid flow rates and fluid viscosity for adequate transport and placement into the fractures. In the present work inorganic polymers were used as coatings to prepare silica proppant with superior strength properties. The physical properties of these inorganic polymers are largely determined by their composition. They are made of a solid inorganic network having an amorphous three-dimensional structure that significantly increased silica proppant compressive strength. The resulting coated proppant materials show an excellent tolerance to high closure stresses (over 10,000 psi) while their apparent specific gravities are slightly lower than sand (2.55 to 2.6 g/cm~3 ). Imaging studies show very homogeneous, well-distributed layers around the sand particles, suggesting a successful coating process.