This project sought to quantify pressure fluctuations and fluid fluxes that could be expected in the far field for large scale CO2 storage in the Surat Basin; in an effort to reduce the risk for implementing large-scale CCS.
It focussed on regional to basin-scale modelling scenarios of the Precipice Sandstone, the overlying Evergreen seal and potential for impacts to the overlying Hutton aquifer.
A commercial reservoir simulator (Eclipse300TM) was used to run simulations of CO2 injection into a water-filled formation. First, a series of simulations were run on a simplistic idealised generic numerical model to establish the key factors affecting groundwater resources. This was done in order to understand how different processes interact and it bears no relation to any real CO2 injection site. Later, the methodology established from these simplistic generic simulations was applied to evaluate the effects of a large-scale CO2 injection in a more realistic regional Surat Basin model. A static geological model which was built for the ZeroGen Project was made available by the Queensland Geological Survey for this study. This static model was modified before use in the dynamic simulations. Pressure and salinity changes, at different locations in the groundwater and storage formations, were extracted from the numerical model forecast during and after the simulated CO2 injection. All of the simulations in this study were at the basin-scale and plume-scale effects which require finer scale grids were not investigated.
Previous studies have shown that pressure propagation in CO2 storage formations due to commercial-scale injection has a larger radius of influence than the plume of free-phase CO2 . As a result, it is expected that some portion of the brine residing in storage formations migrates away either vertically through top seal or laterally in the storage formation potentially towards updip shallow sections of the reservoir or even to the surface.
Therefore, when considering the impacts of geosequestration on groundwater resources, the potential for lateral displacement of saline formation water in the far-field of the injection site and its migration through the seal needs to be characterised. A new method has been developed to assess the possible impact of CO2 injection on groundwater resources by tracking salinity changes in a numerical model forecast. In all of the simulation scenarios the pressure build-up remains less than the fracture or threshold pressure of the seal.