THE MINERALOGY AND PETROLOGY OF THE PERMIAN SANDSTONES AT GIDGEALPA, SOUTH AUSTRALIA

Abstract

Detailed mineralogical and petrographic examinations were carried out on the gas-bearing Permian sandstones at Gidgealpa, South Australia, on behalf of Delhi Australian Petroleum Ltd. The investigation was carried out to obtain data on the possible formation damage during drilling. The rocks consist dominantly of clay-cemented protoquartzites and contain sedimentary and rare (?)granitic rock fragments in the upper members, and acid volcanics fragments in the lower members. The matrix consists of kaolin, illite and quartz. Some of the kaolin is authigenic and consists of vermicular kaolinite. Silicification of the rocks is a common feature, and its effect on the recovery of petroliferous constituents is considered significant. Treatment of the clays with artesian water, saline solution and drilling mud filtrate revealed no modification to the crystal structures, but flocculation of the clays with salt solution was evident. The significance of the laboratory characteristics of these samples to their behaviour in situ is discussed.