Abstract
The Sydney basin, Australia, contains nearly 200 boreholes, many fully cored for coal resource evaluation, as well as outcrops of Early Triassic fluvial systems deposited during late-stage filling of a foreland basin. Lithofacies mapping defined three stratigraphic sequences consisting of deposits of four principal fluvial systems. Within these sequences reservoir quality is highly variable; permeability is a function of original sand mineralogy and texture and thus is closely related to paleogeography and facies of the fluvial systems. A set of visual permeability standards (encompassing five orders of magnitude) was used for continuous permeability estimation of cores from 15 geographically and geologically representative wells. Accuracy of estimates was monitored by laboratory analysis of 540 core samples. Meter-by-meter permeability estimates were combined to produce a suite of quantitative maps and cross sections showing the areal and stratigraphic distribution of reservoir quality. Contouring was strongly guided by the quantitative lithofacies maps that incorporated data from all drill holes and outcrops. Permeability mapping is an important element in ongoing prospect evaluation in the basin. Stratigraphic distribution of reservoir quality records the increasing importance of cratonic source areas through time. Within depositional systems, permeability fairways are closely associated with major fluvial channel axes. Regional west-to-eastmore » decrease reflects a pervasive diagenetic overprint on facies-related heterogeneities.« less
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