Journal of MMIJ (Jun 2024)
Numerical Simulation of Tectonic Stress State Considering The Multiscale Heterogeneity of Geological Structures
Abstract
The development and utilization of deep underground is known to cause induced seismicity that could inflict devastating damage and pose a serious risk for safety and production. Notwithstanding the effort made in the past, a difficulty still lies in estimating the risk for induced seismicity especially taking place in geological structures. To address this problem, the present study numerically investigates stress states of multi-scale geological structures, namely kilometer-scale sedimentary basin and meter-scale fractured rock mass in a fault damage zone. The numerical simulation result of the sedimentary basin revealed that when the bedrock stiffness is higher than that of the reservoir, the differential stress of the reservoir noticeably increases, hence rendering its mechanical stability lower. In contrast, when the stiffness is lower compared to the reservoir, stress concentration takes place in the caprock because the stiffness of caprock is generally higher than that of the reservoir, causing the increase in the differential stress and thus decreasing its stability. The small-scale analysis of the fractured rock mass in a fault damage zone indicated that the complex, fracture-induced stiffness heterogeneity generates a meter-scale heterogeneous stress state on the fault plane. It was further demonstrated that the shear stress distribution on the fault plane particularly plays a key role in the occurrence of induced seismicity rather than the normal stress because of the wide variation ratio of the shear stress. By combining the results, it was then concluded that the meter-scale heterogeneity could cause seismic events with magnitudes of up to 1.0 at a depth of 2000 m, whilst more intense seismic events necessitate stress concentration affected by large-scale geological structures. However, a further study is needed to explore and quantify characteristics of seismicity taking place in multi-scale geological structures, including the dynamic behaviour and faulting type.
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