A review of available surface and subsurface datasets in the coal-bearing geological Gloucester Basin was conducted to build a first-order regional geological model. As a modelled representation, it is based on available data inputs at the time it was built and is one possible representation among many.
The Gloucester basin geological model represents an interpretation of the underground geometries and lithologies. The interpretation is based on wells, outcrop and geophysical data and accounts for the uncertainties and resolution inherent in these data. The well data helps to define the limits between the different geological units as well as the lithology. The uncertainty in these data increases as the distance from the wells increases. Geophysical data (mostly seismic reflection data) were used to extrapolate the data calibrated at the wells and to define a basin-scale fault population.
As the density of both wells and geophysical data is low in the geological Gloucester Basin, isopach maps (i.e. stratigraphic thickness maps) were used to define the basin-scale architecture of the sequences. Each isopach map was calibrated against well picks at the formation scale and constrained by trends observed within each interval. Defining a reference horizon and stacking of the successive isopach maps resulted in an initial non-faulted and non-eroded geological model. Major fault trends were added to allow for major misfits between the non-faulted geomodel and the formation tops at wells.
A fault population was established for the Gloucester subregion based on data from the Stratford CSG Prospect area, where AGL Energy Limited (AGL) proposes to extract coal seam gas (CGS), and published data for other sedimentary coal basins in Australia, New Zealand and the United Kingdom.
The Gloucester subregion geological model can be updated and refined with additional or new datasets and can be populated with hydraulic properties derived from stratigraphic facies.
The geology of the Gloucester subregion is summarised in companion product 1.1, the context statement for Gloucester subregion (McVicar et al., 2014). This summary was based on review of existing literature.
The construction of the Gloucester three-dimensional geological model was based on the understanding gained from this review as well as analyses of available deep well and geophysical datasets. Details of these datasets are provided in Section 2.1.2.1 about observed data.
The methods used to generate derivative datasets and their use in producing the three-dimensional geological model are described in Section 2.1.2.2 about statistical analysis and interpolation.
