Crustal Deformation in the Hutubi Underground Gas Storage Site in China Observed by GPS and InSAR Measurements

Underground gas storage (UGS) facilities are important in the global natural gas delivery chain. Here, we examine continuous Global Positioning System (GPS) observations and Interferometric Synthetic Aperture Radar (InSAR) time series to investigate the regional crustal deformation and seismic hazard associated with the Hutubi UGS (HUGS) facility in the Xinjiang Uygur Autonomous Region, currently China’s largest UGS site. The results indicate that the ground surface subsides slightly during spring, dramatically during summer and gently during autumn, and uplifts slightly during winter. The vertical deformation in the HUGS area is dominated by changes in the subsurface water level. The impact of the ∼50
m lowering in the groundwater level during summer on the source signal at the Hutubi Non-explosive Active Source Station (HUNAS) cannot be ignored during seismic waveform data processing. The rapid uplift from June 2013 to October 2014 reflects rapid elastic or plastic rebound of the UGS cap rock related to longterm compression during oil exploitation prior to 2013. The maximum uplift and subsidence values are estimated to be 15.5 and −13:7 mm, respectively, consistent with the gas well pressure changes. An increase or decrease of 1 MPa in the gas pressure produces 2.63 mm of uplift or 2.11 mm of subsidence, respectively. The monthly pore-pressure changes caused by gas injection and withdrawal vary from −0:071 to 0.093 MPa. These variations are large enough to induce small earthquakes at the HUGS site, which were observed by the local seismic network between 2013 and 2016. The risk of moderate- to strong-magnitude earthquakes in the HUGS region cannot be ignored in the future due to the large gas storage