High Strength, Ultralightweight Proppant Lends New Dimensions to Hydraulic Fracturing Applications

Abstract

Summary Since the earliest fracturing treatments more than 50 years ago, many different materials have been used including sand, glass beads, walnut hulls, and metal shot. Today's commonly used proppants include various sands, resin-coated sands, intermediate-strength ceramics, and sintered bauxite—each employed for its ability to cost-effectively withstand the respective reservoir closure stress environment. As the relative strength of the various materials increases, so too have the respective particle densities, ranging from 2.65 g/cm3 for sands to 3.4 g/cm3 for the sintered bauxite. Unfortunately, increasing particle density leads directly to an increasing degree of difficulty with proppant transport and a reduced propped-fracture volume for equal amounts of the respective proppant, thereby reducing fracture conductivity. Intuitively, one expects that a lesser-density proppant would be easier to transport, allowing for reduced demands on the fracturing fluids, and if it had sufficient strength, would provide increased width, and hence, enhanced fracture conductivity. Previous efforts undertaken to employ lower-density materials as proppant have generally resulted in failure because of insufficient strength to maintain fracture conductivity at even the lowest of closure stresses (1,000 psi). Recent research on material properties has at last led to the development of an ultralightweight (ULW) material with particle strength more than sufficient for most hydraulic fracturing applications. The current ULW proppants have apparent specific gravities of 1.25 and 1.75 g/cm3. Laboratory tests will demonstrate exceptional fracture conductivity at stresses to 8,000 psi. This paper presents data illustrating the performance of the new ULW proppant over a broad range of conditions and a discussion of relative performance in field applications.