HAZA-48 - Using Geodetic Remote Sensing to Measure and Model the Impacts of Gas Extraction from the Surat Basin, Australia

Interferometric Synthetic Aperture Radar (InSAR) is a proven geodetic imaging technique that makes use of remotely sensed radar imagery to map spatial patterns of ground surface movement and their temporal evolution. One application of the InSAR technique is to monitor human interactions with the landscape, such as the extraction of resources from the crust. The increasing demand for gas in Australia has led to increased extraction of unconventional coal seam gas (CSG) reserves, particularly in the Surat Basin in south-east Queensland. Proved and Probable reserves of CSG now exceed 32,000 Petajoules, making the Surat Basin the largest onshore gas reserve in Australia. The geological target of CSG extraction in the Surat Basin is the Walloon subgroup of the Jurassic period, which is typically between 300 to 600 metres depth. Production of CSG from the Walloon subgroup began in 2006 and reserves are currently being extracted by several operators, with combined extraction exceeding 160 Petajoules in 2013-2014. Predictions of the magnitude of subsidence in the Surat Basin based on analytical poroelastic models and quoted CSG production rates indicate that total subsidence on the order of a decimetre may occur. In this contribution we will present new InSAR analysis of the Surat Basin using multi-sensor SAR imagery spanning the 2006-2015 time period. Should patterns of subsidence be detected over the producing gas fields, we will use a geophysical inversion scheme to characterise the objective function between the spatial InSAR observations and predictions of a simple analytical model. Our methodology will make use of a Monte-Carlo sampling algorithm run on High Performance Computing architecture to efficiently sample the multi-dimensional parameter space. The homogenous poroelastic model we employ has dependence on the depth and thickness of the target geological unit as well as on the unit’s rock properties (porosity, Young’s Modulus, Poisson’s Ratio and Shear Modulus). Given that limited information about these properties is generally publically available for the Surat Basin, the geophysical inversion scheme will enable a sensitivity analysis to be conducted that will allow us to understand uncertainties and what parameters have the most significant impact on the system. This in turn will enable more accurate predictions of future subsidence using the poroelastic model. In 2014, Geoscience Australia installed a regional geodetic network over a sub-region of the north-eastern Surat Basin in the vicinity of the towns of Dalby, Miles and Chinchilla in Queensland. The network covers a region of approximately 20,000 km2 and consists of 40 co-located corner reflectors and survey marks. Ongoing SAR imaging of the corner reflectors and periodic campaign GNSS surveys on the survey marks will enable InSAR analysis to be combined with ground-based geodetic measurements and as a result, refine the geodetic reference datum in this region. Preliminary analysis of the persistent scatterer response of the corner reflector network will form a part of this contribution. A dense archive of Interferometric-Wide-Swath (IWS) and Extra-Wide-Swath (EWS) Sentinel-1A images is currently being acquired over the region since the permanently deployed corner reflectors are being used as targets for ongoing geometric and radiometric calibration of the Sentinel-1A SAR sensor. InSAR analysis of this Sentinel-1A data will also form a part of this contribution. Presented at the 2016 Living Planet Symposium (LPS16) Prague, Czech Republic