Earth scientists have long known that fluid injected into the Earth’s crust can induce earthquakes. In principle, seismic activity may also be triggered through gas extraction through the mechanism of poroelastic stress perturbation, although such events have been observed less frequently. In recent years, to meet the growing demand for natural gas, many nations have constructed large underground gas storage (UGS) facilities, into which gas is cyclically injected and then extracted. Because local earthquakes could damage such facilities and shatter the caprock integrity, it is important to understand how gas injection might induce earthquakes.
In a new paper, LML External Fellow Jiancang Zhuang and collaborators at The Chinese University of Hong Kong and University of Science and Technology of China report on a systematic investigation on earthquakes associated with cyclic natural gas injection and extraction in the Hutubi underground gas storages (UGS) facility, Xinjiang, China. Located in the southern margin of the Junggar Basin, the Hutubi UGS facility was originally a natural gas field. After it was depleted in 2009, it was subsequently converted into a UGS with a capacity of 10.7 billion cubic meters, the largest of its kind in China. A study last year concluded that a series of earthquakes in recent years were induced by both pore pressure changes and a poroelastic response, although it remains unclear if these earthquakes were directly induced by gas injection or extraction.
Zhuang and colleagues conducted a statistical analysis of the local earthquake catalog to identify the seismicity rate changes and to highlight earthquakes which could be distinguished from the background seismicity. Their analysis suggests that gas injection had directly induced seismicity adjacent to the Hutubi UGS site, and that these earthquakes were not hydrologically connected with the reservoir formation. Rather, they argue, the induced seismicity was caused by poroelastic stress perturbations associated with gas injection. As the authors note, the results highlighted the importance of near-filed seismic monitoring for UGSs to mitigate the risks of earthquakes induced by gas injection and extraction.
The paper is available at https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019JB017360