RESERVOIR DEVELOPMENT AND DIAGENESIS IN THE BASS BASIN, TASMANIA

Abstract

Drilling and testing in the Bass Basin during 1985-86 indicated that reservoir quality of the lower Eastern View Group is one of the major factors determining the prospectivity of the basin. This study utilises an integrated sedimentological analysis to determine depositional environments of the various reservoirs, and documents the nature and effects that subsequent diagenesis has had on those reservoirs.

During the Paleocene, deposition of the lower Eastern View Group took place within a progradational delta complex in a restricted marine environment. Sandstone bodies deposited in high-energy environments are the best potential reservoirs at depth. Thick, permeable reservoir sands occur in the northern sector of the basin as often-stacked, shoreline facies and in the southern sector as upper delta plain stacked point-bars.

In medium- to coarse-grained quartzose sandstones good reservoir characteristics can be preserved down to depths of 3000 m. Variations in permeability in sandstones with high porosity are related to microporosity associated with pore-filling kaolin. Finer grained sandstones, with higher detrital illite and lower quartz contents, have little effective porosity preserved owing to compaction.