Earthquakes Triggered by Fluid Diffusion and Boosted by Fault Reactivation in Weiyuan, China Due to Hydraulic Fracturing. Issue 5 (2nd May 2022)

• Record Type: Journal Article
• Authors: Sheng, Minhan; Chu, Risheng; Peng, Zhigang; Wei, Zigen; Zeng, Xiangfang; Wang, Qingdong; Wang, Yong
• Is Part Of: Journal of geophysical research. Volume 127:Issue 5(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-05-02
• Subjects: induced seismicity -- shale gas -- Weiyuan; Geomagnetism -- Periodicals; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 551.1
• DOI: 10.1029/2021JB022963
• Languages: English
• ISSNs: 2169-9313

Abstract

Abstract: Hydraulic fracturing has induced small‐to‐moderate‐size earthquakes around the world. Identifying spatio‐temporal evolution of microseismicity is important for understanding the physical processes that control hydraulic fracturing‐induced seismicity. In this study, we build an enhanced earthquake catalog from continuous seismic data recorded by 1‐year temporary deployment with an automatic procedure and relocate 18, 663 earthquakes in the Weiyuan shale gas block in the southern Sichuan Basin, China. Our catalog, with a maximum M L of 3.5, has a completeness magnitude ( M c ) of 0.4, which is ∼23 times more events than listed in the standard National Earthquake Data Center (NEDC) of China. Most earthquakes are clustered near hydraulic fracturing wells and delineate many pre‐existing faults in the north‐south direction. The space‐time evolution of microearthquakes indicates fluid diffusion processes as the primary drivers for seismicity in this region. The fast earthquake migration patterns show that permeability within a fault zone could be affected by fault‐valve behaviors and enhanced by earthquake rupture process. We find that the Gutenberg‐Richter b ‐values increase systematically with depth, and b ‐values further away from hydraulic fracturing pads are generally low, especially for three strands with relatively high migration velocities. Our results confirm that earthquake clusters in Weiyuan are induced by hydraulic fracturing and the reactivated faults act as conduit networks for fluid flow, which promote triggering of earthquakes further away from the hydraulic fracturing pad. This study provides additional evidence for hydraulic fracturing‐induced earthquake in the southern Sichuan Basin and advances our understanding of injection induced earthquakes. Plain Language Summary: The Weiyuan area in the stable southern Sichuan Basin, China recently has experienced increasing seismicity since shale gas mass production. Spatio‐temporal evolution of these earthquakes is important for understanding the physical processes that control hydraulic fracturing induced seismicity. In this study, we build an enhanced earthquake catalog with a completeness magnitude ( M c ) of 0.4 from continuous seismic data recorded by 1‐year temporary deployment and relocate 18, 663 events in the Weiyuan area. Most events are clustered near hydraulic fracturing wells and delineate many pre‐existing faults in the north‐south direction. We then analyze spatio‐temporal migration and b‐value changes of the seismicity, and find that earthquake clusters in the Weiyuan area are induced by hydraulic fracturing mainly through pore fluid diffusion. The reactivated faults act as conduit networks for fluid flow, which promote triggering of earthquakes further away from hydraulic fracturing pads. Fault‐zone permeability may also be affected by fault‐valve behaviors and can be enhanced by recent fault ruptures. This study provides additional evidence for hydraulic fracturing induced earthquake in the southern Sichuan Basin and advances our understanding of injection induced earthquakes. Key Points: Earthquakes in the Weiyuan shale gas block delineate complex fault systems near hydraulic fracturing wells Spatio‐temporal migration of the seismicity reveals pore fluid diffusion as the primary triggering mechanism Earthquake b ‐values systematically decrease with increasing depth and their variations may be affected by fault behaviors