ABSTRACT: Sedimentary Facies Analysis of an Evolving Glacial Sequence, the Permian-Carboniferous Grant Group, Canning Basin, Western Australia

REDFERN, JONATHAN, Fina Far East Pty Ltd., Cecil Court, Singapore, and EMMA D. MILLWARD, University of Aberdeen, Aberdeen, Scotland

Within the Canning basin, the Permian-Carboniferous Grant Group is one of the main hydrocarbon reservoir targets. Previous studies have been limited to the accessible scattered outcrops and sparse subsurface data. However, the recent acquisition of a series of stratigraphic boreholes, located on the Barbwire Terrace, provides fully cored sections through the Grant Group. These have been integrated with wireline log data to allow detailed sedimentary facies analysis and regional correlations.

The Grant Group comprises sediments deposited by an extensive ice sheet, which covered the Canning basin during the Late Paleozoic. The cored sections exhibit a complex suite of glaciogenic facies, an evolving glacial sequence, recording the glaciation and gradual deglaciation of the basin, with evidence of periodic ice advantage and retreat cycles.

Diamictites, mudstones, and thick sandstones at the base of the section are interpreted to be proximal glacial deposits. The overlying thick mudstone package, followed by a heterolithic/sandstone facies association, are interpreted to be post glacial deposits. The glacial sandstone units have excellent reservoir potential, while interbedded lacustrine mudstones and massive muddy diamictites form effective seals.

Analysis of a number of widely spaced wells and the correlation of three recently defined formations, allow these reservoir units to be placed within a stratigraphic framework. This provides an understanding of the reservoir distribution, while displaying the complex nature and spatial variability of individual glaciogenic facies.

AAPG Search and Discovery Article #91015©1992 AAPG International Conference, Sydney, N.S.W., Australia, August 2-5, 1992 (2009)