12:00 〜 12:15
[HSC05-12] CO2地中貯留などの流体圧入による誘発地震と自然地震を区別する手法の開発
キーワード：誘発地震、自然地震、間隙水圧、CO2地中貯留、モニタリング、貯留層シミュレーション
In countries located at plate convergent margins (e.g., Japan), many natural earthquakes occur every day. To obtain a public understanding of CO2 storage projects, we need to develop a method for distinguishing between natural earthquakes and those induced by CO2 injection. For example, the 2004 Mw 6.8 Chuetsu earthquake occurred close to the Nagaoka CO2 storage site during gas injection, but we could not quantify whether or not the earthquake was due to CO2 injection. The earthquake generation can be evaluated mainly based on the following parameters: pore pressure, effective stress, frictional coefficient of the fault plane, and shear stress across the fault. If the shear stress is larger than the frictional force of the fault, earthquakes will likely occur. During CO2 injection, while the frictional coefficient, effective stress, and shear stress could be almost constant, only pore pressure is varied. Therefore, the pore pressure could be an important factor in evaluating induced seismicity.
We have recently developed an approach to monitor the spatiotemporal pore pressure in wide areas (Nimiya et al., 2017; Andajani et al., 2020). Using this method, we identified the natural pore pressure variation due to rainfall, snowmelt, and remote earthquakes. On the other hand, we can also estimate changes in pore pressure during the CO2 injection using reservoir simulation (i.e., CO2-water fluid flow simulation). To distinguish between CO2 injection-induced earthquakes and natural earthquakes, we compared (1) the natural pore pressure variations and (2) the variation due to CO2 injection.
This study simulated pore pressure changes at the Nagaoka CO2 storage and compared these changes with estimated natural seasonal fluctuations in pore pressure (Chunn and Tsuji, 2020). Changes in pore pressure due to CO2 injection were clearly distinguished from those due to rainfall and snowmelt. The simulated pore pressure increase near the seismogenic fault area was much smaller than the seasonal fluctuations related to precipitation and stress increases caused by remote earthquakes. The lateral extent of the pore pressure increase was probably insufficient to influence seismogenic faults. We also demonstrated that large pore pressure changes due to distant earthquakes could trigger slip on seismogenic faults. This approach is simple, but the method is based on numerical stress calculations ; thus, we can quantitatively interpret the earthquake around the CO2 injection site. The approach will be useful at other CO2 sequestration sites and geothermal operations. We should consider the shear stress and poroelastic behaviors due to CO2 injection in this way to provide more quantitative evaluations of possible earthquake triggering. .
References:
1) Andajani, R. D., T. Tsuji, R. Snieder, and T. Ikeda (2020), Spatial and temporal influence of rainfall on crustal pore pressure based on seismic velocity monitoring, Earth, Planets and Space, 72:177, doi:10.1186/s40623-020-01311-1.
2) Chhun, C., and T. Tsuji (2020), Pore pressure analysis for distinguishing earthquakes induced by CO2 injection from natural earthquakes, Sustainability, 12, 9723; doi:10.3390/su12229723
3) Nimiya, H., T. Ikeda, and T. Tsuji (2017), Spatial and temporal seismic velocity changes on Kyushu Island during the 2016 Kumamoto earthquake, Science Advances, Vol. 3, no. 11, e1700813, doi:10.1126/sciadv.1700813.
We have recently developed an approach to monitor the spatiotemporal pore pressure in wide areas (Nimiya et al., 2017; Andajani et al., 2020). Using this method, we identified the natural pore pressure variation due to rainfall, snowmelt, and remote earthquakes. On the other hand, we can also estimate changes in pore pressure during the CO2 injection using reservoir simulation (i.e., CO2-water fluid flow simulation). To distinguish between CO2 injection-induced earthquakes and natural earthquakes, we compared (1) the natural pore pressure variations and (2) the variation due to CO2 injection.
This study simulated pore pressure changes at the Nagaoka CO2 storage and compared these changes with estimated natural seasonal fluctuations in pore pressure (Chunn and Tsuji, 2020). Changes in pore pressure due to CO2 injection were clearly distinguished from those due to rainfall and snowmelt. The simulated pore pressure increase near the seismogenic fault area was much smaller than the seasonal fluctuations related to precipitation and stress increases caused by remote earthquakes. The lateral extent of the pore pressure increase was probably insufficient to influence seismogenic faults. We also demonstrated that large pore pressure changes due to distant earthquakes could trigger slip on seismogenic faults. This approach is simple, but the method is based on numerical stress calculations ; thus, we can quantitatively interpret the earthquake around the CO2 injection site. The approach will be useful at other CO2 sequestration sites and geothermal operations. We should consider the shear stress and poroelastic behaviors due to CO2 injection in this way to provide more quantitative evaluations of possible earthquake triggering. .
References:
1) Andajani, R. D., T. Tsuji, R. Snieder, and T. Ikeda (2020), Spatial and temporal influence of rainfall on crustal pore pressure based on seismic velocity monitoring, Earth, Planets and Space, 72:177, doi:10.1186/s40623-020-01311-1.
2) Chhun, C., and T. Tsuji (2020), Pore pressure analysis for distinguishing earthquakes induced by CO2 injection from natural earthquakes, Sustainability, 12, 9723; doi:10.3390/su12229723
3) Nimiya, H., T. Ikeda, and T. Tsuji (2017), Spatial and temporal seismic velocity changes on Kyushu Island during the 2016 Kumamoto earthquake, Science Advances, Vol. 3, no. 11, e1700813, doi:10.1126/sciadv.1700813.