Temperature and Fluid Pressurization Effects on Frictional Stability of Shale Faults Reactivated by Hydraulic Fracturing in the Changning Block, Southwest China

Abstract

A shale fault reactivated during multistage 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°C, 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°C and velocity weakening at temperatures of 250–300°C. Increasing the pore fluid pressure can increase values of (a − b) at temperatures ≥200°C, narrowing the temperature range where velocity weakening occurs. At the in situ temperature (90°C), the simulated gouge shows only velocity strengthening behavior and aseismic slip at elevated pore fluid pressures, contrary to the observed seismicity. We postulate that the aseismic slip at elevated pore fluid pressures may trigger seismicity by activating adjacent earthquake‐prone faults.

Frictional stability of Longmaxi shale gouges and its implication for deep seismic potential in the southeastern Sichuan Basin

“…The gouge SSC3740‐2 shows a higher tectosilicate content but a lower phyllosilicate content than the gouge SSC3730‐1. Compared with many previous research works (An, Zhang, Chen, et al, 2020; Chen et al, 2015; Fang et al, 2018; Kohli & Zoback, 2013), the mineral compositions are shown to be an important factor for shale fault stability.…”

“…As the depth of the target reservoir increases, the potential for fault instability and hazard of induced seismicity will increase dramatically. Although temperature is not the main factor controlling seismicity in the shallow shale reservoirs (An, Zhang, Chen, et al, 2020), the high temperature can impact the fault stability in deep shale reservoirs. Additionally, the mineral composition of the deep Longmaxi shale reservoir varies significantly and may also favor velocity‐weakening behavior at increased depths.…”

Fault Slip Risk Assessment and Treating Parameter Optimization for Casing Deformation Prevention: A Case Study in the Sichuan Basin

“…We observe that the microseismic events from these three stages are all far away from the perforation locations. The multistage events overlap and converge into a microseismic event band, which conforms to the characteristics of fault activation [34][35][36][37][38]. The microseismic event band coincides with fault #1 spatially, and its extension direction is also consistent with the strike of fault #1.…”

Numerical Modeling Study on Mineral Alteration and Sealing Performance for CO2 Geological Sequestration with Enhancing Water Recovery in Hydraulic Fractured Shale Reservoirs

“…Deformation of the formation will occur because of CO 2 injection. Considering the existence of shale the bedding plane, natural fractures, and faults [39][40][41][42][43][44][45][46][47][48][49][50][51][52][53], the deformation behavior and the effect on fluid transport will be extremely complicated. The reactivation potential of faults does exist, Lithosphere which may provide a leak path for CO 2 to escape the storage formation [54][55][56].…”