Assessing groundwater impacts due to fracture stimulation and pilot testing programs for coal seam gas exploration: Waukivory Pilot Project in the Gloucester Basin, NSW

Full text: Coal Seam Gas (CSG) forms an important component of future domestic gas supply in Australia. Exploration for CSG requires drilling and testing of pilot gas wells to assess the gas resource and likely produced water volumes. In some cases, gas wells are fracture-stimulated; a process of pumping a fluid and sand under pressure into the coal seam to open cleats and fractures at depth, increasing the hydraulic conductivity and enabling the flow of water and gas. Public concern has focussed on a potential connection between target coal seams and shallow groundwater resources, and the perceived risk of water quality impacts. There has been a lack of good quality monitoring information with which to assess these risks, particularly in low permeability Permian Coal Measures. In late 2014 AGL carried out testing of four pilot gas wells at Waukivory within the Stage 1 Gas Field Development Area of the Permian Gloucester Basin, NSW. As part of the pilot testing program, extensive monitoring of groundwater, surface water and gas well produced water was carried out prior to, during and following fracture stimulation and subsequent flow testing. Samples of fracture stimulation fluid were also tested to identify key analytes as indicators of impact to adjacent water resources. No BTEX or chlorine based compounds were used in the fracture stimulation fluid, and none were detected in the fluid samples. This paper presents results from the monitoring program. Interpretation of the results included identification of water level and water quality trends and assessment as to whether apparent trends were naturally occurring or potentially attributed to project activities. The investigation found no clear evidence for enhanced connectivity between target coal seams and shallow groundwater during, and in the three months following fracture stimulation. The results provide important calibration constraints for impact assessment modelling. (author)