Objectives
The ~650 m thick interval from the Hutton Sandstone up to the Springbok Sandstone in the Surat Basin (Queensland, Australia) are aquifers of the Great Artesian Basin. Hydrological modelling of groundwater flow and pressure evolution is an important tool for management of this resource. Stratigraphy and depositional environment are essential to model conception and build as they provide estimates of aquifer geometry and heterogeneity. This study investigates the stratigraphy of the interval of interest with well log data integrated with generally underutilised seismic data.
Design and Methodology
A sequence stratigraphic methodology has integrated seismic, wireline, core and outcrop data regionally at select areas. A 3rd and 4th order sedimentary depositional cycle framework pinned to two regional datums is developed. This framework allows sedimentary packages of same age to be correlated laterally highlighting heterogeneity and connectivity of aquifers. In contrast, most current models use a lithostratigraphic approach to correlate packages of similar lithology which may overestimate the lateral extent and connectivity of aquifers. Environments of deposition are interpreted from lithofacies and lithofacies associations based on core descriptions integrated with well log motifs.
Original Data and Results
An example section of 7 wells tied to 17 seismic sections was extracted out of a larger regional study encompassing more than 600km of seismic lines. The resulting Surat Basin sequence stratigraphy results in a different interpretation of the character of both the Hutton Sandstone and the Springbok Sandstone than previously published (i.e. fluvial–lacustrine). This section is interpreted to be from lower delta plain (distributive channel belts and floodplain), delta front, and tidal depositional settings. Furthermore, the sandstone and coal forming facies aren’t necessarily extensive lithologic units, as depicted in existing correlations.
Conclusions
The evolving Surat Basin sequence stratigraphy framework results in a new geological concept of genesis for these aquifers that may change the fundamental understanding of the connected extent of aquifers in the Hutton-Walloon-Springbok interval. This may significantly affect how fluid flow modelling is used to manage those resources because less continuous, more heterogeneous aquifers transmit pressure and respond to well operations differently depending on the correlation method used to define the modelling domain.