Sliding frictional characteristic of tight sandstone and its influence on the hydraulic fracture complexity

Abstract

The complexity of the fracture network during hydraulic fracturing is closely related to the frictional characteristics of the reservoir rock, which largely depends on the rock’s mineralogical properties and the type of fracturing fluid. In this study, the micro-friction characteristics of three kinds of tight sandstone were tested using an indoor rock micro-friction setup. The effects of different hydraulic fluids and rock mineralogical properties on the friction coefficient were investigated. A numerical model was then developed to investigate the influence of different friction coefficients on fracture propagation. The results indicate that the friction coefficients of tight sandstones are closely related to their content of clay and quartz. When the content of clay is low (around 20%), the content of hard particles such as quartz and feldspar is high, the friction coefficient of the rock appears to be high and insensitive to the wetting characteristics of the fracturing fluid. Conversely, when the clay content is high (around 30%), rock friction coefficients tend to be sensitive to different types of fracture liquids, and decrease when the liquid wets the rock. The numerical simulation results indicate that a 0.4 friction coefficient produces the maximum of fracture complexity. These findings provide a potential method on how to increase the productivity of unconventional plays by generating complex fracture networks.