Townley, L.R. (2015), Potential impacts of CSG production on regional groundwater systems - learnings for shale and tight gas, Water Management for Shale and Tight Gas Resources, 8-9 June, Perth, Co-convened by IAH, SPE and ASEG WA Chapters.

CSG is fundamentally different from shale gas and tight gas, because water must be removed to reduce pressures until CSG is released by desorption. It is important to understand the differences, and at the same time to recognise challenges and risks, whether real or perceived.

The emergence of a coal seam gas (CSG) industry in Australia has been accompanied by concern about potential impacts on regional aquifers, including the Great Artesian Basin. The volumes of water withdrawn during production of CSG need to be understood in the context of water use from all sources, including surface water and groundwater. Nevertheless, prediction of the potential impacts of CSG production has been difficult, for a number of reasons, including the limitations of readily available commercial off-the-shelf (COTS) groundwater modelling software and a lack of understanding of the differences between approaches taken by reservoir engineers and hydrogeologists.

One objective of this paper is to explain some differences between methods used by reservoir engineers and hydrogeologists, and why traditional groundwater modelling, without modification, is not capable of predicting the quantity and quality of groundwater produced during gas production.

  • Multiphase reservoir models (e.g. based on ECLIPSE) predict desorption of gas, migration of gas towards production wells and co-production of water, but are not designed to predict regional impacts at the water table or where coal seams sub-crop alluvial aquifers.

  • Regional scale groundwater flow models (e.g. based on MODFLOW and FEFLOW) represent changes in storage of water in a fundamentally different way, and cannot without modification predict rates of production of water or depressurisation to match the predictions of reservoir models.

    A number of CSG projects have been approved in Australia in recent years. This paper will compare and contrast approaches taken to predict potential impacts on regional aquifers, as described in publicly available Environmental Impact Statements, and based on additional personal experience. Reference will be made to regional scale groundwater flow modelling in the Surat, Bowen, Gunnedah-Oxley, Perth and West Canning Basins. While spatial variability is known to contribute to prediction uncertainty in reservoir and hydrogeological modelling, representation of boundary conditions, including the surface boundary condition, is especially important in predicting the response of aquifers to stress. Reference will also be made to challenges related to bore integrity, and the impact of leaky bores on cross-formational groundwater flow and transport.


    Copyright © 2015 by Lloyd Townley
    Last revised: 7 July 2015