Temperature and fluid pressurization effects on frictional stability of shale faults reactivated by hydraulic fracturing in the Changning Block, Southwest China

A shale fault reactivated during multi-stage hydraulic fracturing in the Changning block in the Sichuan Basin, southwest China accompanied a cluster of small earthquakes with the largest reaching ML ~0.8. We illuminate the underlying mechanisms of fault reactivation through measurements of frictional properties on simulated fault gouge under hydrothermal conditions. Velocity-stepping experiments were performed at a confining pressure of 60 MPa, temperatures from 30 to 300 ℃, pore fluid pressures from 10 to 55 MPa and shear velocities between 0.122 and 1.22 μm/s. Results show that the gouge is frictionally strong with coefficient of friction of 0.6-0.7 across all experimental conditions. At observed in-situ pore fluid pressure (30 MPa), the slip stability response is characterized by velocity strengthening at temperatures of 30-200 ℃ and velocity weakening at temperatures of 250-300 ℃. Increasing the pore fluid pressure can increase values of (a – b) at temperatures ≥ 200 ℃, narrowing th...

中国西南地区四川盆地长宁区块的一条页岩断层在多段水力压裂期间发生复活，伴随出现一群小地震，其中最大震级达ML~0.8。我们通过在热液条件下对模拟断层泥（fault gouge）的摩擦特性进行测量，阐明了断层复活的内在机制。在围压60MPa、温度30~300℃、孔隙流体压力10~55MPa、剪切速度0.122~1.22μm/s的条件下，开展了速度阶跃实验（velocity-stepping experiments）。结果表明，在所有实验条件下，该断层泥的摩擦强度均较高，摩擦系数介于0.6至0.7之间。在观测到的原位孔隙流体压力（30 MPa）下，滑动稳定性响应表现为：温度30~200℃时呈速度强化（velocity strengthening）特征，250~300℃时呈速度弱化（velocity weakening）特征。在温度≥200℃时，提高孔隙流体压力可增大(a–b)值，缩小...