Fracability evaluation of shale reservoirs considering rock brittleness, fracture toughness, and hydraulic fracturing-induced effects

Abstract

Fracability is a vital evaluation index for shale reservoir exploration and development and horizontal well fracturing. In this paper, we define the fracability of a shale reservoir as the ability of hydraulic fracturing to generate a complicated large-scale fracture network and large stimulated volume under the same stimulation parameters. Considering factors such as the shale sedimentary environment and confining pressure, we establish a brittleness index calculation method by coupling logging data and in situ rock mechanics test results to obtain parameters such as the reservoir Young's modulus and Poisson's ratio. According to the fractal method, an in situ rock bifurcation/irregular fracture toughness calculation method is established. The hydraulic fracture-induced index is introduced to reflect the influence of stimulation-induced displacement, reservoir seepage, fluid viscosity, horizontal principal stress difference and other parameters on fracability. A fracability evaluation method coupling the reservoir rock brittleness, fracture toughness and hydraulic fracture-induced index is formed. The results of the field application show that the established method can effectively characterize the ability of a reservoir to form complex fracture networks and promote the stimulation effect. This study provides more credible guidance for geological and engineering practices for developing shale reservoirs.