HOT SEDIMENTARY AQUIFER CHARACTERIZATION USING STRATIGRAPHIC FORWARD MODELLING, PERTH BASIN, AUSTRALIA

摘要

Several geothermal projects in the Perth Metropolitan Area, Western Australia, have already demonstrated the geothermal potential of the area for aquifers down to 1 km depth. The Western Australian Geothermal Centre of Excellence (WAGCoE) was tasked with assessing the potential of deeper aquifers. Members of WAGCoE, in collaboration with CSIRO, investigated the use of stratigraphic forward modelling (SFM) techniques combined with geothermal reservoir definition to identify potential geothermal reservoirs in locations where data are sparse. The major aquifer and low-temperature geothermal target in the Perth Basin, the Yarragadee Aquifer, provides a major portion of Perth's drinking water. Although the shallow part of the Yarragadee Aquifer has been well studied by hydrogeologists, the deeper part is still poorly characterized. Using the stratigraphic forward modelling package Sedsim, the sedimentation of the Yarragadee Formation was simulated over a period of 15.8 Ma. The simulation was calibrated against sparse seismic surveys, petroleum wells and core data. The final simulation volume was uplifted and eroded to the current state of the Yarragadee Formation, providing estimates of facies, grain size and porosity distributions for the entire formation. Once the characterization of the Yarragadee Formation was achieved, the identification of geothermal reservoirs required investigating the suitability of the subsurface to deliver the energy required for a given geothermal application. Based on simple assumptions such as constant thermal conductivity, uniform geothermal gradient, and using pre-defined geothermal production design settings such as flow rate and maximum pressure drop, parameters such as the reservoir temperature and the reservoir producible power are evaluated. As different geothermal applications have different subsurface requirements, reservoirs are individually investigated for a specific geothermal applications. This methodology has been developed to allow rapid investigation of the local geothermal potential while changing the surface geothermal application requirements.