NATURE OF POROSITY IN SOME INDURATED PERMIAN SANDSTONES FROM THE COOPER BASIN

Abstract

The percentage porosity measured by physical means is commonly much larger than apparent porosity (measured as void space) seen in thin sections. This occurs even where the thin section is cut from the plug actually used for measurement and when extreme care is taken in preparing the section.

This discrepancy has led to a consideration of the properties of pores and this paper reviews classifications based on size, fabric selectivity and genesis. A basic distinction between pores related to sedimentational features and those derived from diagenesis and/or tectonism is stressed.

In Permian sandstones from the Cooper Basin porosity is present largely as pores less than 0.06 mm across. These generally cannot be seen in thin section nor can they be related to observable petrographic features of the rocks.

Secondary micropores and submicropores in the Cooper Basin rocks may be due to either diagenetic or tectonic activity; the overall spatial variation of porosity and permeability may indicate which process has been more important.