固体地球物理专业研究生学术论坛——唐兰兰

Hutubi gas field, the largest gas storage field in China that has been operated on annual injection/extraction cycles since 9 June 2013. We study the seismicity near the gas field from 9 June 2013 to 22 October 2015, and explore its physical mechanism based on the relationship between seismicity and field operation. We identify 273 events (ML >1) in the region within 10 km of the gas field, with 97% of those occurring in the first and second injection periods, 0.4% in the third injection period and 1% in the two extraction periods. Seismicity in the first two injection periods occurs mostly as shallow clusters (depth < 2 km) at two locations: with one along the fault that marks the southern boundary of the gas field and the other about 2 km south to the southeastern tip of the gas field with the seismicity distributed along north-south direction. The seismicity does not correlate with total gas injection volume, injection rate or well pressure. It instead occurs 11-17 hours after simultaneous abrupt increases/decreases of gas injection rate and well pressure in the field operation. Such relationship is consistent with a physical mechanism that the seismicity near Hutubi gas field is induced on pore-pressured faults with a rate- and state-dependent friction law through an abrupt change of stress in elastic and undrained poroelastic responses to simultaneous abrupt changes of injection rate and well pressure. Our study also points to the possibility that induced seismicity may be controllable in some practical field operations.