Wu Haiqing, Vilarrasa Victor, De Simone Silvia, Saaltink Maarten, Parisio Francesco
Department of Civil and Environmental Engineering (DECA) Universitat Politécnica de Catalunya (UPC) Barcelona Spain.
Associated Unit: Hydrogeology Group (UPC-CSIC) Barcelona Spain.
J Geophys Res Solid Earth. 2021 Jan;126(1):e2020JB020436. doi: 10.1029/2020JB020436. Epub 2021 Jan 19.
Displaced faults crossing the reservoir could significantly increase the induced earthquake frequency in geo-energy projects. Understanding and predicting the stress variation in such cases is essential to minimize the risk of induced seismicity. Here, we adopt the inclusion theory to develop an analytical solution for the stress response to pore pressure variations within the reservoir for both permeable and impermeable faults with offset ranging from zero to the reservoir thickness. By analyzing fault stability changes due to reservoir pressurization/depletion under different scenarios, we find that (1) the induced seismicity potential of impermeable faults is always larger than that of permeable faults under any initial and injection conditions-the maximum size of the fault undergoing failure is 3-5 times larger for impermeable than for permeable faults; (2) stress concentration at the corners results in the occurrence of reversed slip in normal faults with a normal faulting stress regime; (3) while fault offset has no impact on the slip potential for impermeable faults, the slip potential increases with the offset for permeable faults, which indicates that non-displaced permeable faults constitute a safer choice for site selection; (4) an impermeable fault would rupture at a lower deviatoric stress, and at a smaller pressure buildup than a permeable one; and (5) the induced seismicity potential is overestimated and the injectivity underestimated if the stress arching (i.e., the poromechanical coupling) is neglected. This analytical solution is a useful tool for site selection and for supporting decision making during the lifetime of geo-energy projects.
穿越储层的错动断层会显著增加地热能项目中诱发地震的频率。了解和预测此类情况下的应力变化对于将诱发地震活动的风险降至最低至关重要。在此，我们采用夹杂理论来推导一个解析解，用于求解储层内孔隙压力变化时，偏移量从零到储层厚度的可渗透和不可渗透断层的应力响应。通过分析不同情况下储层增压/减压导致的断层稳定性变化，我们发现：（1）在任何初始条件和注入条件下，不可渗透断层的诱发地震潜力总是大于可渗透断层——发生破坏的断层最大尺寸，不可渗透断层比可渗透断层大3至5倍；（2）在正断层应力状态下，角部的应力集中会导致正断层出现逆滑；（3）虽然断层偏移量对不可渗透断层的滑动潜力没有影响，但可渗透断层的滑动潜力随偏移量增加，这表明未错动的可渗透断层是更安全的选址选择；（4）不可渗透断层在较低的偏应力下以及比可渗透断层更小的压力增量下就会破裂；（5）如果忽略应力拱效应（即孔隙力学耦合），诱发地震潜力会被高估，而注入能力会被低估。这个解析解是地热能项目选址以及在其整个生命周期内支持决策制定的有用工具。
