Enhancing geological and hydrogeological understanding of the Precipice Sandstone aquifer of the Surat Basin, Great Artesian Basin, Australia, through model inversion of managed aquifer recharge datasets

Phil Hayes,Ahmed Harfoush,Sebastian Gonzalez,Chris Nicol,David Gornall,Lauren Helm,Jianhua He,Andrew Moser,Julie Pearce,Jiahao Wang,Ryan Morris,Andrew D La Croix

doi:10.1007/s10040-019-02079-9

Abstract

The Precipice Sandstone is a major Great Artesian Basin aquifer in the Surat Basin, Queensland, Australia, which is used for water supply and production of oil and gas. This report describes use of observed groundwater pressure responses to managed aquifer recharge (MAR) at a regional scale to test recent geological descriptions of Precipice Sandstone extent, and to inform its hydrogeological conceptualisation. Since 2015, two MAR schemes have injected over 20 GL of treated water from coal seam gas production into the Precipice Sandstone, with pressure responses rapidly propagating over 100 km, indicating high aquifer diffusivity. Groundwater modelling of injection and inversion of pressure signals using PEST software shows the spatial variability of aquifer properties, and indicates that basin in-situ stresses and faulting exert control on permeability. Extremely high permeability, up to 200 m/day, occurs in heavily fractured regions with a dual-porosity flow regime. The broader-scale estimates of permeability approach an order of magnitude higher than previous studies, which has implications for the management of water resources in the Precipice Sandstone. Results also show the Precipice Sandstone to have broadly isotropic permeability. The results also support a recent geological interpretation of the Precipice Sandstone as having more limited lateral extent than initially considered. The study shows the effective use of MAR injection data to improve geological and hydrogeological understanding through groundwater model inversion. It also demonstrates the utility of combining hydrogeological and reservoir-engineer datasets in areas explored and developed for both groundwater resources and oil and gas resources.

Highlights

Hydrogeological understanding of the Great Artesian Basin’s (GAB) Surat Basin (Queensland, Australia) has progressed over the last 8 years due to the rapid development of coal seam gas (CSG, known elsewhere as coal bed methane) industry, which extracts groundwater from the Walloon Coal Measures coal seams to produce gas
The highest transmissivity values are centred on the Spring Gully Managed Aquifer Recharge (MAR) injection site and in an area to the northwest of that site and bounded by the Hutton-Wallumbilla Fault
The relatively localised very high permeability zone at Spring Gully, and a lesser degree Reedy Creek, may have implications elsewhere in the GAB where sandstones have been subject to extensional stress regimes

Summary

Introduction

Hydrogeological understanding of the Great Artesian Basin’s (GAB) Surat Basin (Queensland, Australia) has progressed over the last 8 years due to the rapid development of coal seam gas (CSG, known elsewhere as coal bed methane) industry, which extracts groundwater from the Walloon Coal Measures coal seams to produce gas. Regulation of the CSG industry by the Queensland Government has included declaration of a cumulative management area (CMA) (Fig. 1), within which overlapping impacts from multiple CSG projects are assessed by the Office for Groundwater Impact Assessment (OGIA). The extraction of CSG requires reduction of pressure in the coal seams to release gas. The pressure reduction is achieved by extracting groundwater, and this associated water requires management by the CSG industry. Much of the CSG water is reused for irrigation, typically after some treatment such as reverse osmosis, to decrease the total dissolved solids (Towler et al 2016). Another use of the water is the artificial recharge of the Precipice Sandstone by two Managed Aquifer Recharge (MAR) schemes

Results

Discussion

Conclusion