A Study On InSAR Deformation Detection Of Induced Seismicity In Changning Shale Gas Block,Southern Sichuan Basin

In recent years,with the expansion of shale gas exploitation in China,a series of microseismicity,felt earthquakes,and even destructive earthquakes occurred in the southern Sichuan Basin,a relatively tectonic stable area.Some studies statistically infer whether these earthquakes were induced by industrial activities using spatiotemporal correlations.Existing research mostly starts from the perspective of seismology and numerical simulation.Taking the Changning shale gas block as an example,this paper analyzes whether shale gas exploitation can produce detectable ground deformation from the perspective of deformation observation,analyzes the relationship between deformation information and shale gas exploitation,and tries to provide an effective means of monitoring for shale gas exploitation.This paper uses L-band ALOS-2 data for monitoring.Long-wave ALOS-2 satellite radar data can minimize the decorrelation effects of radar signals caused by vegetation,humidity,and complex terrain in the Sichuan Basin.Based on this data,this paper detects the InSAR surface deformation of the Changning shale gas block in the past 2to 3 years,detecting the possible ground deformation and its basic characteristics caused by the large-scale exploitation of shale gas.The results show that sufficient ground deformation can be generated during shale gas exploitation.The deformation presents non-steady state characteristics,and it can also be effectively monitored by InSAR technology.From the interferogram,it can be distinguished that shale gas exploitation will cause rapid uplift or decline of the ground.At the same time,this paper also uses Sentinel-1 satellite radar data to analyze the deformation time series information during the active period of shale gas development.During the four years from 2015 to 2019,the cumulative uplift of locations with more significant uplifts in the study area reached ?30 mm.The cumulative subsidence of locations with larger subsidences reached ?15 mm.The ground also has horizontal deformation.Considering the different error levels and observation angle between the two satellite observation techniques.Both satellite data reflect a consistent distribution of surface deformation.Furthermore,the measured deformation field is in agreement with the spatial distribution of shale gas wells.Based on the effective deformation information observed by InSAR,we have gained several insights:(1)Under the complex deformation observation conditions in the southern Sichuan Basin,InSAR technology can be as an effective monitoring method for shale gas exploitation.It can supplement the deficiencies of seismological observations.(2)When performing deformation monitoring in the Sichuan Basin,since the Lband ALOS-2 data signal will be affected by the changes in the electron density in the ionosphere,according to the dispersion characteristics of the ionosphere,the range split-spectrum method can be used very well on eliminating the ionospheric phase.(3)Using permanent scatterer time series processing technology to process C-band Sentinel-1 data,a sufficient number of point targets in the shale gas exploitation area can be identified.PS points phase information of the study area include serious atmospheric delay phase,long-wave error phase and look angle error phase,etc.These error phases need to be estimated and eliminated to obtain effective deformation information.(4)The deformation rate value within 15-16 km of the Sentinel-1 profile suddenly changed from positive to negative,and the south wing of the Jianwu syncline developed a fault fractured zone with a width of about 2 km.The fault fractured zone can be seen on the seismic reflection profile of the Changning shale gas exploitation area.In comparison with the deformation field,there is a dense distribution of shale gas production wells on the north side of the fractured zone,and the ground uplift is obvious.The northern boundary of the fractured zone may become an obstacle to fluid diffusion.Therefore,the area on the south side will not uplift and the deform behavior is similar to that of elastomers.(5)The results show fast surface uplift during hydrofracture injection.In the production period with fluid diffusion,ground subsidence and horizontal motion are observed.InSAR analysis results preliminarily reveal the non-steady deformation characteristics during shale gas exploitation.