Gossmann, S., Herbert, St.J., Tovar, M., Townley, L., and Brooker, A. (2012), Modelling connections between aquifers in the CSG industry, APPEA 2012 Conference, Adelaide, 13-16 May.

Development of conventional and unconventional gas resources including CSG share many similarities; however, some important differences in CSG extraction may lead to potential impacts on groundwater supply. Conventional gas reservoirs are usually located at greater depths than commonly exploited groundwater resources. This contrasts with the situation in the CSG industry in which the targeted coal seams for CSG extraction are shallower and may be inter-layered with hydrostratigraphic units (HSUs) that contain usable groundwater resources.

Formation depressurisation during CSG extraction has the potential to diminish pressure and groundwater storage within bounding aquifers that may be used for agricultural, industrial, and urban water supplies. For example, groundwater transfer from shallow aquifers to underlying CSG units may occur preferentially in areas where the CSG units subcrop beneath shallow aquifers, possibly at sigmficant distances from operating wells. Within this context Arrow Energy is investigating the connectivity between HSUs.

This extended abstract focuses on the use of numerical groundwater models to simulate potential impacts of CSG extraction, with particular emphasis on the behaviour of models in the contact area between the CSG units and overlying shallow alluvial aquifers. Aspects of model grid design and how horizontal and vertical hydraulic conductivities are assigned at the interface between target coal seams and bounding aquifers are explored. This localised sub-region within a regional-scale groundwater flow model has the potential to control the estimates of flows that are of most interest to groundwater stakeholders.