Groundwater monitoring for an LNG project in Surat Basin, Queensland, Australia
The Australia Pacific liquefied natural gas (APLNG) project involves the production of coal seam gas (CSG) in numerous tenements across the Surat Basin in southeast Queensland. CSG production requires depressurisation of the coal seam by groundwater pumping from gas production wells.
KCB was commissioned by Origin Energy (Origin) to provide hydrogeological field supervision services for the installation of groundwater monitoring bores throughout their gas-producing operations and pilot facilities. By installing groundwater bores, Origin expanded its regional monitoring network for the long-term monitoring of groundwater aquifers for potential impacts of CSG activities on water pressure and water quality. In addition, these bores are used to provide information on hydraulic properties and local aquifer characteristics.
Landowner Bore Baseline Assessment
This project involved a regional assessment of bore condition and groundwater quality, undertaken on privately owned bores throughout the Surat Basin. It was undertaken on behalf of Origin to provide independent background data for tenements where gas production or testing had commenced, and was conducted in accordance with the Queensland Department of Natural Resources and Mines Baseline Assessment Guideline.
A total of 452 bores were included in the program on approximately 200 properties spread over an area of 400 km2. Assessments at each bore included measurements of free gas, water levels, pumping rates, water quality sampling (where possible) and recording of the dimensions and general condition of the bores.
Aquifer Injection Trials
Origin had conducted aquifer injection trials, of treated CSG water, into the selected units of the Great Artesian Basin (GAB) for water management purposes, and KCB was asked to predict the groundwater response to these trials. The injection of treated CSG water is now part of the project’s operational water management strategy.
The project evaluated the potential impact on key aquifers of the GAB and on selected Town Water Supply Bores after 60 days of proposed injection at different bore sites.
Key project tasks included:
- modification of existing model grid and remnant boundary conditions in proximity to the injection site;
- establishment of pre-injection steady state conditions inclusive of the anticipated effects of Town Water Supply Bores in the area;
- modeling of injection for a set period of 60 days under 3 scenarios; and
- particle tracking of physical injection fate and generation of head contours for key aquifers at multiple time steps, for each of the scenarios run under Best-Estimate and Max-Impact conditions
Spring Gully Injection Modelling
The objective of the injection modelling project was to evaluate the ratio of CSG water to natural flow over a period of 16 years in the Precipice Sandstone aquifer at Spring Gully.
The project involved predictive modelling of the injection of CSG water, with the application of a FEFLOW groundwater model. The model was developed under three case scenarios – Best-Estimate, Maximum-Impact and Minimum-Impact – associated with specific target aquifer parameters. The model development required boundary conditions and pre-injection steady state conditions to be quantified. The model also addressed particle tracking and head contour development over a period of five hundred years.
For each of the scenarios, the injection well injects for 16.5 years while the public supply boreholes pump continuously for 1,000 years. The head rise at the injection site was contoured at the end of the injection.