Getting water from gas production
To produce coal seam gas (CSG), wells are drilled into underground coal seams, bringing associated groundwater from the seams to the surface. This process lowers pressure in the seams which allows gas to be released.
The extracted water is naturally rich with salts and other minerals, which means it generally needs to be treated before it can be made available for potential beneficial uses. A small portion of the water is used for operational purposes, but most is treated and supplied for other beneficial uses including replenishing groundwater supplies via a process called aquifer injection.
As part of the Queensland Government’s CSG management strategy, any potential use of this produced water requires rigorous analysis and engineering before it can be approved. It must benefit one or more of: the environment, existing or new water users, or existing or new water-dependant industries in a way that minimises or avoids any detrimental impact on the environment.
When considering aquifer injection as an option, a number of stringent approval conditions must also be met to make sure the water quality in the receiving aquifer is not negatively impacted as a result of the reinjection.
Replenishing the Great Artesian Basin
As upstream Operator for Australia Pacific LNG (APLNG), Origin operates two groundwater injection borefields in central southwest Queensland, at Reedy Creek and Spring Gully.
Unlike the CSG wells that extract gas and associated groundwater water, these purpose-built bores are used solely for the purpose of returning treated water produced by CSG production back into the Precipice Sandstone aquifer – a major Great Artesian Basin aquifer in the Surat Basin, Queensland.
The Great Artesian Basin (GAB) is one of the world’s most iconic and largest groundwater basins, stretching more than 1.7 million square kilometres. Over the past 100 years, groundwater decline has been observed in the GAB as a result of use for pastoral, agricultural and extractive industries as well as for many town water supplies.
Researching the potential of aquifer injection
Several years of research and investigations were undertaken to understand the technical, economic, and socio-environmental risks and benefits relating to aquifer injection within APLNG’s Queensland gas fields.
Origin hydrogeologists assessed aquifer recharge schemes in Australia and worldwide and consulted with international experts including CSIRO to identify candidate sites for field investigations. During field investigations at three sites across the gas fields, Origin worked with researchers within the Gas Industry Social and Environmental Research Alliance (GISERA). GISERA is a collaboration between CSIRO, Commonwealth, State and Territory governments, and the gas industry
Injection trials at multiple sites targeted three different aquifers – the Precipice Sandstone, Hutton Sandstone, and Gubberamunda Sandstone. The results of the investigations and field trials identified that aquifer injection into the Precipice Sandstone would be a feasible water management solution at the Spring Gully and Reedy Creek injection sites.
Recharging groundwater supplies
Reedy Creek was the first injection scheme, commissioned in early 2015. At the time of its launch, it was the largest treated water managed aquifer recharge scheme in Australia.
Purpose built bores were drilled at depths of up to 1,400 meters to inject treated water into the Precipice Sandstone aquifer. Thick, low permeability layers of rock separate and restrict connection between the Precipice Sandstone and the aquifers above and below. Since coal seam gas production began, approximately 81 per cent of the water produced at Reedy Creek gas fields has been used to replenish the Precipice Sandstone aquifer via aquifer injection.
Since 2018, approximately 16 per cent of the water produced at the Spring Gully gas field has also been injected, with most treated water from Spring Gully directed to local landholder irrigation scheme for beneficial use.
In total, more than 37 gigalitres of treated water has been returned to underground water supplies in the past seven years. This volume is more than twice the amount of water the Queensland Government estimates was pumped by existing users from the Precipice Sandstone aquifer in the area over the same timeframe for various water use purposes.
Increased aquifer pressures have also been observed at distances of more than 100km from the injection facilities. Importantly, this water is available to existing and new groundwater users. It’s anticipated that over the next 30 years, more than 100 gigalitres will be injected into the Precipice Sandstone aquifer.
