Publication Name: The Sedimentary Basins of WA
Authors: N.P. Tupper, S.E. Phillips and B.P.J. Williams
Publication Volume: 1
Date Published: July 1994
Number of Pages: 26
Reference Type: Book Section
Abstract:
A detailed evaluation of the Upper Permian sequence in the north Perth Basin has resulted in a better understanding of reservoir distribution and quality. Biostratigraphy, sedimentology, petrology and log analysis have been combined to explain reservoir character in the Upper Permian gas fields. Models for reservoir prediction have highlighted areas for further exploration.Deposition of the Wagina Formation was controlled by the interaction of tectonic and eustatic processes. Movement on the Darling Fault instigated half-graben development and syn-rift deposition within terrestrial,
shoreline and marine environments. However, the lateral extent and vertical stacking of depositional facies was
also influenced by relative changes in sea level.
Reservoir quality is controlled principally by diagenesis, with depositional facies only a secondary influence. Three different reservoirs are recognised, based on the distribution of authigenic clays and carbonates. Quality is excellent at shallow depths in the north of the basin, where kaolin is dominant, but below 2700 m silicification and compaction of the sandstone have progressively reduced primary porosity. In the basin centre, chlorite and illite rims have inhibited quartz cementation in restricted zones, preserving sandstone porosity to much greater depths. Limestone is developed in the south, and although carbonate cementation has occluded primary porosity fracturing, recrystallisation and dissolution have created sporadic secondary porosity and permeability.
Exploration for Upper Permian plays in the north Perth Basin can continue with greater confidence now that reservoir quality can be more accurately predicted. In particular, recognition of preserved porosity in sandstone with chlorite or illite rim cements has improved the prospectivity of deeper areas in the basin.