Methane in Great Artesian Basin aquifers: emission factors for groundwater pumping and coal seam gas produced water
Julie Pearce A * and Harald Hofmann B CA
B
C Present address:
Dr Julie Pearce has international experience in the UK, Japan, and Australia on interdisciplinary projects, and is currently an ARC Mid-career Industry Fellow at the University of Queensland Gas and Energy Transition Research Centre, and School of the Environment. Pearce is an expert on gas-water-rock interactions with a focus on CO2 geological storage. She is currently working on field-based techniques for measurement of dissolved gases and understanding potential methane leakage processes and inter-aquifer connectivity through geochemical and isotopic techniques. Julie is collaborating in research projects with the gas and CO2 storage industries and has provided expert opinion to the Government. |
Dr Harald Hofmann joined CSIRO in January 2024 after 10 years at the University of Queensland in an academic teaching and research role. He completed his PhD in Hydrogeology at the Monash University in 2012, followed by a post-doctoral position focusing on stable and cosmogenic isotope hydrology to understand catchment water residence times. Dr Hofmann’s current research interests include the development of conceptual groundwater models, including groundwater flow and quality characterisation, of coastal aquifer systems and sedimentary basins. He is a leading expert on perched groundwater system linked to groundwater dependent ecosystems. |
Abstract
High volumes of groundwater are pumped from aquifers or naturally released through springs or seeps. In the Great Artesian Basin (GAB) various industries, agriculture, feedlots, town water supply, and private landholders extract groundwater. In a component basin, the Surat Basin, coal seam gas (CSG) is also extracted from the Walloon Coal Measures. Gassy water bores can cause pump locks, and other hazards for landholders. High concentrations of dissolved and free gas have been measured in different GAB aquifers, both above and below the CSG reservoir. For example, deep water bores sampled in the Hutton and Precipice sandstone aquifers contained up to 2100 mg/L dissolved methane. CSG production water contained up to 31 mg/L methane. Dissolved methane was sampled via several methods, and emission estimates determined using estimated pumped water volumes and measured methane concentrations. New emission factors were determined for groundwater pumping, and for CSG production water. The existing emission factors for CSG production water (used by the Australia Government) were taken from a USA emission factor originating from a simulation study. We found it to be an order of magnitude higher than emission factors determined from our data. We conclude that: (1) current CSG produced water emission factors may not represent Australian conditions and overestimate emissions; and (2) current standard dissolved methane sampling is not fit for purpose, especially for gassy bores and hot deep groundwaters.
Keywords: aquifer, coal bed methane, coal seam gas, dissolved methane, Great Artesian Basin, groundwater, methane emissions, production water, Surat Basin.
Dr Julie Pearce has international experience in the UK, Japan, and Australia on interdisciplinary projects, and is currently an ARC Mid-career Industry Fellow at the University of Queensland Gas and Energy Transition Research Centre, and School of the Environment. Pearce is an expert on gas-water-rock interactions with a focus on CO2 geological storage. She is currently working on field-based techniques for measurement of dissolved gases and understanding potential methane leakage processes and inter-aquifer connectivity through geochemical and isotopic techniques. Julie is collaborating in research projects with the gas and CO2 storage industries and has provided expert opinion to the Government. |
Dr Harald Hofmann joined CSIRO in January 2024 after 10 years at the University of Queensland in an academic teaching and research role. He completed his PhD in Hydrogeology at the Monash University in 2012, followed by a post-doctoral position focusing on stable and cosmogenic isotope hydrology to understand catchment water residence times. Dr Hofmann’s current research interests include the development of conceptual groundwater models, including groundwater flow and quality characterisation, of coastal aquifer systems and sedimentary basins. He is a leading expert on perched groundwater system linked to groundwater dependent ecosystems. |
