Understanding the geochemistry associated with reinjecting SCG water into water basins
Coal seam gas production can require the management of large quantities of brackish water, called 'produced water', that is extracted with the gas. Queensland regulation require this water to be treated before it is released into the environment. It can then be discharged into rivers and dams, provided to nearby farmers or reinjected into aquifers as part of an aquifer managed recharge scheme. This last option is appropriate when other options are unable to continuously manage the volumes of 'produced water' from CSG wells allowing this water resource to be used at a later time without evaporation consequences.
Reinjection of this water contributes to the long-term sustainability of the industry through generating benefits for agriculture. However, despite extensive water treatment, there is, depending on local conditions, a possibility that the reinjected water may react with minerals in the aquifer, allowing for mobilisation of metals and / or metalloids. For this reason, a detailed understanding of the geochemistry associated with aquifer reinjection is necessary to predict and manage water quality and risks for the receiving aquifers.
Proven economic and technical feasibility
The Surat Basin is now the major source of CSG in Queensland. In 2015-16 production from the Surat Basin was over 22 billion cubic meters, more than four times that of the Bowen Basin. Also in 2015-16, Queensland's 5127 CSG wells reported producing 60,499 megalitres of associated water.1 The present project is the first of its kind to examine the potential for using aquifer managed recharge methods in generating sustainable outcomes for produced CSG water in the Surat Basin.
Planning for this project started in 2009-10. From the start, Origin Energy, a partner in Asia Pacific LNG (APLNG), had a strong collaborative relationship with the CSIRO GISERA team throughout this project. State and Federal environmental approvals required aquifer injection trials to be undertaken. By proving technical and economic feasibility, operational injection was able to be considered as part of the suite of CSG water management options.
CSIRO was able to draw on its previous research on using highly treated wastewater for recharging deep aquifers in Western Australia. The project took place over a four-year period in which CSIRO undertook research, with Origin Energy performing all necessary field work, including drilling.
The project has preceded the planned reinjection of approximately 80 megalitres per year of treated CSG produced water by Origin Energy. This water resource will then be available for future agricultural use such as crop irrigation.
A successful CSG water reinjection project
This CSG produced water reinjection project has:
- Enabled the effective and sustainable operation of the Reedy Creek CSG operation
- Created, at the time, Australia's largest reinjection scheme
- Resulted in industry uptake of research findings and scientific know-how
- Enabled the Queensland Government authorisation of the injection scheme
- Addressed a potential arsenic pollution problem associated with the reinjection of CSG produced water
- Allowed safe indirect re-use of produced water from CSG operations at Reedy Creek by farmers for crop irrigation and other users of the Precipice Sandston Aquifer
- Provided confidence in the preservation of the groundwater asset in the Surat Basin by recharging a depleted aquifer with CSG produced water
- Contributed to successful development of the Commonwealth’s Government’s Domestic Gas Strategy and its implementation through the Domestic Gas Strategy Implementation Plan.