The Influences of Mineral Components and Pore Structure on Hydraulic Fracture Propagation in Shale

The microscopic mineral composition has an important impact on the mechanical properties of rock. By the computed tomography (CT) scanning, the mineral composition inside the shale core samples drilled from the Jimsar shale oil reservoir was identified. The numerical model of shale was established using an image reconstruction technique and basic mechanical parameters of mineral composition were obtained by nanoindentation tests. The influences of mesoscopic geotechnical properties (mineral components and porosity) and artificial parameters (perforation direction, perforation spacings, and fracturing fluid viscosity) on hydraulic fractures were investigated using a coupled hydraulic-mechanical (HM) model. The results indicate that the initial consecutive fractures control the propagation trace of hydraulic fractures and significantly reduce the stress shadow effect. The mineral particles and discrete pore structure are beneficial to the branching of fractures. Under the same fracturing strategy, an increase in the proportion of quartz promotes the complexity of hydraulic fractures. The increment of porosity after fracturing is negatively correlated with the initial porosity. For models without initial consecutive fractures, the complexity of hydraulic fractures and the stimulated volume increase with the decreasing fracturing fluid viscosity and increasing perforation spacing. The brittleness index determined by mineral components is closely related to post-fracturing porosity, which can provide references for optimizing hydraulic fracturing.