Dataset: Predictive modelling of potential groundwater impact pathways from shale gas development


Description

Abstract

The dataset was compiled by the Geological and Bioregional Assessment Program from source data referenced within the dataset and/or metadata. The processes undertaken to produce this derived dataset are described in the History field in this metadata statement. Five key potential impact pathways were identified in GBA stage 2. These included hydraulic impacts, which involve the propagation of reductions in pressure (known as “drawdown”) away from a groundwater bore field used to supply water to a shale gas production well. Reductions in pressure are also applied during hydraulic fracturing of shale gas production wells, in order to cause gas to flow. Drawdown can propagate either directly (e.g., when an aquifer or gas reservoir is in contact with another aquifer) or indirectly (e.g., via an intervening aquitard, or via a geological fault, which can act as a conduit). Analytical groundwater flow models were used to estimate potential hydraulic impacts (in terms of changes in pressures and flows) resulting from likely groundwater and shale gas extraction activities. Three workflows based on local scale impact models were successfully used to provide predictions of potential hydraulic impacts. For the simulation of drawdown impacts that propagated upward via an intervening aquitard, the effects of faults on aquitard vertical hydraulic conductivity were addressed. The assumptions required by each model were stated explicitly, and conservative parameter values were able to be chosen in most instances. Modelling results indicated that hydraulic impacts are likely to be negligible, as aquitard sequences are generally thick (i.e. hundreds of metres). Conversely, relatively larger drawdown impacts were predicted in areas where aquifers or aquitards were thin, and/or where fault zones were present.

Attribution

Geological and Bioregional Assessment Program

History

For the Cooper GBA region, spatially distributed saturated thickness data were obtained from the "Cooper Basin Source Rock Atlas 2016/01/01" dataset. The locations of fault traces were obtained from the "Great Artesian Basin major geological structural elements" dataset.

For the Beetaloo GBA region, spatially distributed saturated thickness data were obtained from the "GA Regional Three-Dimensional Geological Model for the Beetaloo Sub-basin" dataset. The locations of fault traces were obtained from the following dataset:

Betts, P., Armit, R., and Ailleres, L. (2015). Geophysical and structural interpretation of the greater McArthur Basin. Northern Territory Geological Survey, Digital Information Package DIP015, https://geoscience.nt.gov.au/gemis/ntgsjspui/handle/1/81754.

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