Pore-scale damage evolution in sandstone induced by fluid infiltration under various stress conditions

Abstract

While stress-dependent fluid infiltration plays a critical role in the initiation and propagation of hydraulic fractures, limited attention has been paid to the dynamics of fluid infiltration and the pore-scale damage mechanisms resulting from fluid infiltration during hydraulic fracturing. To address these research gaps, this study conducts hydraulic fracturing experiments on tight sandstone under various stress levels, employing nuclear magnetic resonance (NMR) techniques to monitor real-time fluid infiltration behavior. Results reveal that continuous fluid injection alters pore compressibility by regulating effective stress distribution and anisotropic fluid infiltration, causing macropore evolution shifting from compression to expansion under increasing in situ stresses. Interestingly, elevating the differential stress lowers the rock breakdown strength by promoting fluid infiltration and macropore modification, though excessive high stress differences can cause water blocking. Anisotropic fluid infiltration is confined to a finite damage volume surrounding the fracture, while higher differential stresses promote fracture propagation along preferential infiltration paths. A refined damage length model is developed to characterize varying infiltration lengths across different stress levels. We recommend implementing stress relief measures to reduce formation breakdown strength, utilizing anisotropic infiltration to enhance fracture complexity and employing a primary fluid infiltration path to predict hydraulic fracture initiation. These findings offer new insights into hydraulic fracture nucleation mechanisms and can help improving field hydraulic fracturing operations in tight gas reservoirs.