Provenance and Facies Controls on Porosity and Permeability Distribution in Latrobe Group Sandstones, Gippsland Basin, Australia

Michael J. Hayes

Provenance and depositional facies are primary controls on porosity and permeability distribution in Latrobe Group sandstones of the Gippsland Basin, Australia. Provenance determines the mechanical and chemical stability of framework grains and potential diagenetic pathways during burial. Compaction of lithic fragments and precipitation of quartz and kaolinite cements degrade reservoir quality in lithic Latrobe sandstones, where intergranular volume (IGV) approaches zero locally because a stabilized rigid grain framework is unattainable. In contrast, quartzose Latrobe sandstones attain a stabilized IGV of approximately 25% upon closest packing of quartz grains.

The facies control on reservoir quality results from depositionally controlled variations in grain size, sorting, detrital clay matrix, and sand thickness. Relatively coarse-grained, well-sorted, matrix-free, thick-bedded facies including upper shoreface, tidal- and fluvial-channel sands have good reservoir potential. Relatively fine-grained, thin-bedded, matrix-rich and lithic-rich lower shoreface and coastal plain sands form poorer reservoirs.

Favorable provenance and facies lead to preservation of economic porosity at depth where IGV is not infilled with cement. Decreases in porosity and IGV and increases in quartz and clay cements at equivalent depths correspond with a shift towards lithic-rich sandstones. This case study underscores the value of an integrated approach to reservoir quality assessment. Petrographic, core and well-log data should be evaluated with respect to provenance and facies, not only depth and temperature, when developing predictive models for porosity and permeability distribution.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995