Abstract
The Lower Jurassic Precipice Sandstone is an important hydrocarbon and water reservoir in the Surat Basin. It is the basal infill of the Surat Basin, commonly considered an intracratonic sag basin, although the triggering mechanism for subsidence remains unresolved. Its interpreted origin is a fluviatile system that formed a thick belt of sandstone that corresponds to the Mimosa Syncline structural axis. The Precipice Sandstone outcrops along the northern margin of the basin forming laterally continuous cliffs. This provides good conditions for 2D and 3D photogrammetry and classical analysis of sedimentary architectures, bedding and facies. Photogrammetry is a measurement technique that builds 3D photorealistic virtual models in which every pixel on the image corresponds to a real 3D point in georeferenced space. This was used to measure surfaces, correlate stratigraphy, and to measure bed and body geometries for export to a reservoir modelling system, providing a bridge between the subsurface drilling data and the outcrop analogue. The field survey mapped the lower Precipice, defined by the predominance of southeast-flowing planar and trough cross stratified sandstone (the braided stream facies), and upper Precipice, defined by a predominance of heterolithic, ripple and plane parallel stratification and slumps that transition upward into the Evergreen Formation mud-dominated unit. Sedimentary structures in outcrop suggest a northward flow on the eastern margin of the outcrop for the upper Precipice. The basin asymmetry, coincident with a major, meridional-trending fault system—the Goondiwindi-Moonie-Burunga system—and changes in upper and lower unit thickness suggest some syn-depositional control on the sedimentary architecture.
Published Version
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