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Impact of sequence stratigraphy on static and dynamic reservoir models: examples from the Precipice-Evergreen succession, Surat Basin, Queensland

CO2 storage in the subsurface is a key aspect of climate mitigation. The UQ is investigating whether the Precipice Sandstone and Evergreen Formation in the Surat Basin, Queensland, are an appropriate reservoir-seal pair for the long-term storage of greenhouse gases. However, the Precipice-Evergreen succession remains poorly constrained from a paleo-depositional and stratigraphic standpoint. Studies have mostly applied lithostratigraphy for local correlation, and the understanding of time-stratigraphic relationships across the basin needs development. This has greatly hindered the capacity to construct robust reservoir models and is an active area of research. We utilized core, wireline logs, seismic reflection surveys, and pressure data to compare the dynamic response to various CO2-injection scenarios with contrasting stratigraphic architectures. A lithostratigraphic prediction of reservoir and seal intervals consisted of a layer-cake model of fluvio-deltaic deposits. The models suggest that reservoir layers are laterally well-connected with the gas plume primarily migrating parallel to bedding. In contrast, a sequence stratigraphic arrangement of facies resulted in a more complex architecture, where reservoir and non-reservoir strata cross-cut and intersect one another. The resulting models showed greater reservoir heterogeneity and potentially more complex fluid transmission pathways in both the lateral and vertical directions that could result in slower plume migration and more residual trapping. This is due to the fact that discontinuous mudstone intervals potentially baffle the CO2 plume and may allow for more CO2 trapping within the lower parts of Evergreen succession. The contrasting models show different geological realizations arising from the same dataset, interpreted in different ways than identify where there is uncertainty. They may highlight certain areas of the basin are more conducive to carbon storage than others. Fluid flow is highly sensitive to the stratigraphic arrangement of reservoir and non-reservoir intervals. Refining static and dynamic models using sequence stratigraphy may result in a significant improvement in history matching. Modellers should carefully consider the implications of stratigraphic correlations during static model construction.