- Chengdu University of Technology, Chengdu, China (hujuan07@cdut.edu.cn)
There is still uncertainty in the mechanisms controlling the increase in earthquake productivity and shale gas development in the southern Sichuan basin of China. In this study we take advantage of a more complete seismic catalog from local seismic stations, as well as injection data for two adjacent hydraulic fracturing wells, during March 2017 to January 2018, to investigate these mechanisms. To ensure the completeness and reliability, two seismic catalogs were effectively merged and uniformly scaled using the moment magnitude Mw scale. A spatiotemporal constraint framework was designed to extract induced earthquakes during the injection stages, and a series of seismic statistical methods were used to study the correlation between 885 earthquakes (Mw 0 to 4.6) and fluid injection. These include the ETAS model, and the nearest-neighbor-distance method. The results suggest most seismicity close to the wells are likely linked to the hydraulic fracturing process. For events associated with the N5 well pad, the cumulative number of earthquakes has a positive correlation with the cumulative injection volume. Through the use of the Seismogenic-Index, the difference of seismogenicity of different wells is obtained. We show that injected volume not only correlates with the number of induced earthquakes, but also correlate with the maximum seismic magnitude in the region. We demonstrate that this can then be used to retroactively forecast the induced seismicity. Although the injection at the two well pads is similar, the N5 pad is associated with many more indued events compared to the N7 pad. Reflection seismic imaging indicates that faults and fractures are well developed beneath the target reservoir of N5, but not for N7. This indicates proximity to preexisting faults/fractures control the occurrence of inducing seismicity in the region. The possible cause of the Mw 4.6 earthquake is briefly analyzed by calculating the range of pore pressure diffusion, and the Coulomb stress change from poroelastic effects. This shows that induced seismicity in the southern Sichuan basin is controlled by both preexisting faults/fractures and injection fluid volume.
How to cite: Hu, J.: The productivity of induced seismicity in the southern Sichuan basin, China is controlled by injected volume and preexisting faults , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13985, https://doi.org/10.5194/egusphere-egu25-13985, 2025.