Inferring the shape of fractures and hydraulic properties of the coal seam using inverse modeling on pumping test results – Broke, NSW, Australia

Coal seam gas or coal bed methane production is becoming a significant industry in Australia. The area around the Broke township (located in the north-west of the Sydney Basin) has had coal seam gas exploration activities over the last decade. One methodology of well stimulation, hydraulic fracturing, has the potential to cause some environmental problems. The Broke region includes 4 aquifers (3 confined and semi-confined), more than 3 major coal seams (3 gas bearing) and has been covered by variety of different sedimentary rocks of Permian age. The groundwater system, with the gas bearing deposits is the function of conductivity and storativity (K and S) of the coal seam and geometry of properties of the fractures. The required data to investigate the hydraulic properties in the fractured zone includes; corehole data to assessment the geology and underground system, micro-seismic data to infer the fracture properties, pumping tests results, and monitoring wells data to evaluate the hydraulic properties of the coal seams. This paper investigates the shape of drawdown curves, resulting from the hydraulic pumping tests at Broke performed to determine the hydraulic and fracture properties, such as length, width, conductivity of fractures, and the proportion of the water and gas contained in the targeted coal seam. In order to reduce data uncertainty and increase the reliability of the hydraulic property estimation the Generalized Likelihood Uncertainty Estimation (GLUE) will be applied. Finally, with investigation of the shape (length and width) and conductivity of the fractures, the best monitoring method to ensure public safety of provide assurances that if problems occur the monitoring system will provide early warning for this study area will be determined.