The geological model of the Hunter subregion was built between June 2014 and early February 2015, during which time data had to be acquired, processed, unified between the different coalfields and filtered to obtain data that could be used in the BA to underpin a regional-scale geological model. While a lot of different geological datasets exist in the Sydney Basin, to manage the data requirements and simplify the analyses in the time available, a decision was made to focus on petroleum well data that are deep enough to give access to different sedimentary units and are relatively homogeneous from one company dataset to another. Before developing the geological model, members of the project team met with geologists from Sydney University and NSW Trade and Investment in order to discuss their approach and obtain data. With more time to acquire and analyse their data and/or collaborate with them in developing the regional model, a refined geological model may have been possible. Areas for improvement include the following:

  • The Hunter subregion geological model is focused on the Permo-Triassic strata and is characterised by a lack of structural constraints and the heterogeneity of the datasets. The Sydney Basin basement structure has been well characterised through the use of deep reflection seismic, magnetic and gravity data (Blevin et al., 2007; Danis et al., 2011), but the link between the Permo-Triassic sedimentary rocks and this deep structure needs to be more closely analysed.
  • The incorporation of well data, which were not publicly available from the DIGS (Digital Imaging Geological System) database at the time when the Hunter geological datasets were being compiled (August 2014) could help to better constrain the geological framework.
  • As explained in the introduction, other types of well data, such as coal and groundwater bores, could be included to add lithological and stratigraphic detail to the shallower levels of the model.
  • Shallow seismic reflection data would improve the mapping of the Permo-Triassic horizon tops across the Hunter subregion.
  • Depth interpretation of the raw seismic data is needed to improve the definition of geological structures in the Permo-Triassic strata. Interpretation reports were provided to the project by NSW Trade and Investment and reviewed by the BA team, but useful calibrated and shallow interpreted (in depth) seismic line data were not obtained. There would be value in reinterpreting the seismic reflection data, calibrating the wells and then converting the data from the time to the depth domain.
  • The model could be updated by incorporating a stochastic distribution of the faults, as was done in the Gloucester Basin case study (Frery et al., 2018). A small displacement along a fault can lead to discontinuities in hydrogeological flow paths. These small-displacement faults are difficult to interpret, especially from onshore seismic data. A power law approach can be the best way to represent these structures in the model. Results from the groundwater modelling in the Gloucester subregion (Peeters et al., 2018) showed, however, that faults had little impact on model results.
  • The lithology and the facies, defined from the general stratigraphic column, can be refined to include hydraulic properties and potential connectivity between horizons.
  • A finer resolution model would permit better integration of the well data and geological complexity in defined areas.

Some of the foregoing deficiencies in the current geological model are compensated for in the groundwater modelling through simulating hydrological changes across a wide range of parameter values which reflect regional differences and account for the uncertainty in the geological model. The groundwater model emulators provide a means of incorporating better local-scale information, where it is available, to constrain the results from the regional groundwater model (see companion product 2.6.2 (groundwater numerical modelling) for the Hunter subregion (Herron et al., 2018). Thus the regional-scale geological model does not need to represent a lot of local detail to be fit for the regional-scale groundwater modelling undertaken for the bioregional assessment.

Last updated:
18 January 2019
Thumbnail of the Hunter subregion

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