Identification of Clay Minerals Within the Springbok Formation, Surat Basin

Abstract

The Springbok Sandstone in the Surat Basin overlies the Walloon Coal Measures, an important coal seam gas resource. Here we investigate the hypothesis that potassium free or low-potassium clay minerals are the dominant clay minerals in the Springbok Sandstone, and review the effect this has on the ability of conventional well log analysis to successfully highlight high clay content rock units within the formation. Core samples from a test well have been analysed showing montmorillonite and kaolinite clays to be the dominant clay minerals within the formation. Schlumberger Lithoscanner well log tool data from the test well has been compared to the laboratory core analysis revealing a good correlation between element concentrations identified by the tool and the laboratory data, however the mineralogy model which has been applied to this dataset does not appear to predict mineral assemblages within the formation successfully. Laboratory results have been compared to an existing conventional well log analysis for the basin, where gamma and density log cutoffs have been used to identify variations in lithology. Our investigation suggests this model does not successfully differentiate between clay rich and clay poor rocks within the Springbok Sandstone, and an alternative model using additional well logs is demonstrated to provide greater insight into lithology variations throughout the formation.