Ground deformation due to natural resource extraction in the Western Canada Sedimentary Basin

Abstract

The study links multiple natural resource extraction activities in the Western Canada Sedimentary Basin (WCSB) with observations of ground deformation. Sentinel-1, RADARSAT-2, and RADARSAT Constellation Mission (RCM) Synthetic Aperture Radar (SAR) data acquired as early as 2015 were used to compute deformation maps and ground deformation time series. Ground deformation produced by induced earthquakes (2015 Mw 4.6 in British Columbia and 2022/23 Mw 5.1/4.6 in Alberta; and 2017/18 Mw 5.0/4.2 slow slip events in British Columbia) were mapped with individual interferograms. Long-lasting ground deformation due to Steam-Assisted Gravity Drainage (SAGD) and Cyclic Steam Stimulation (CSS) enhanced oil recovery and coal and potash underground mining were mapped with the Multidimensional Small Baseline Subset (MSBAS) time series method. When both ascending and descending data were available, MSBAS was used to compute two-dimensional (2D) deformation time series and rates. It was observed that seismic and aseismic ground deformation due to hydraulic fracturing and saltwater injection in WCSB had a similar surface expression (paired anomaly), spatial extent (5-10 km) and orientation (striking NW-SE), suggesting that triggering processes might be technogenic. In the case of hydraulic fracturing, ground deformation appeared soon after the beginning of the operation, while not with saltwater injection, as it took years. The source mechanism of the 2015 Mw 4.6 earthquake was obtained through inverse modelling of the two descending interferograms. The rectangular source model corresponded to a fault at 1.98 ± 0.09 km depth, with 126° ± 7° strike, 14° ± 2° dip, 72° ± 7° rake, 1.61 ± 0.24 km width, 2.54 ± 0.23 km length, and 0.19 ± 0.07 m slip. In the case of in-situ enhanced oil recovery, ground deformation varied significantly depending on the technique. Continuous uplift observed at the SAGD site had a rate of only about 0.05 m/year, while reversible uplift and subsidence at CSS sites exceeded 0.2 m/month, even though wells in both cases were located at approximately similar depths (380 m for SAGD vs 520 m for CSS). In the case of underground mining, the spatial extent of subsidence depended on the extraction depth (200-500 m for coal vs 1000 m for potash). When a mining operation was conducted in an area with topographic relief, horizontal deformation was observed in addition to subsidence. Various observed deformation signals may precede more consequential deformation events.