Faults are important for understanding geothermal systems due to their influence on the stratigraphic structure, and how that structure influences fluid flow. Fault networks influence not only conventional geothermal plays, but also hot sedimentary aquifers. The Western Australian Geothermal Centre of Excellence (WAGCoE ) focuses on hot sedimentary aquifer prospectivity in the state of Western Australia, and particularly in the Perth Basin. A new workflow has been developed by WAGCoE to identify a fault network in urban areas and generate a 3D model of subsurface geology. We apply this methodology to creating a new geological map of the Perth Metropolitan Area (PMA). The approach involves testing hypothetical fault models against progressively more complex data types. An early 3D model without interpreted faults represents the current published understanding of the regional geology, and has been used to model groundwater flow in the region numerically. This model had some inconsistencies with formations derived from shallow water bores. New 3D models were developed that incorporate a new fault network using data from shallow water bores and sparse petroleum wells, gravity surveys and multiscale edge analysis of potential fields (“worms”). One model involves significant flexure of the stratigraphic layers adjacent to the faults, and the other model involves stiffer stratigraphic layers and consequently larger fault displacements. Each model is consistent with the constraints from well data and gravity data, yet produces slightly different aquifer geometries. The newly identified fault network in the geological models is essential for improving subsurface flow models and hence understanding the geothermal temperature distribution in the region. Geothermal potential in Perth is focused on direct use projects whose low-enthalpy resources are available above 2 kilometers in depth. Two other sources of data suggest that the new faulted model of the PMA is consistent with fluid and temperature data. Extensive temperature borehole logging and modeling across the region shows several areas of anomalous temperature distribution near the hypothesized new faults. Calibration of a prior regional groundwater flow model without faults indicates that several areas in the shallow aquifers where simulated head values differ considerably from measured levels. To investigate whether the new faulted model will better account for these two types of data, new flow models have been run to calculate temperature and fluid flux vectors in a cross-section of the Perth Metropolitan Area.

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