QUALITATIVE ANALYSIS OF SPECTRAL GAMMA RAY DATA AS A TOOL FOR FIELDWIDE AND REGIONAL STRATIGRAPHIC CORRELATION, ENDERBY TERRACE, CARNARVON BASIN, WESTERN AUSTRALIA

Abstract

The use of wireline and core spectral gamma data as a tool for defining clay types and mineral assemblages in the subsurface environment has been widely used for many years within the petroleum industry. However, the qualitative use of radiometric data for interpreting rock types as used with airborne surveys in the mineral industry has not undergone detailed assessment as a well correlation tool.

Applying the principles of qualitative airborne radiometric interpretation to the assessment of wireline spectral gamma ray data has proved extremely useful as a well correlation tool in the Carnarvon Basin of Western Australia. Data is presented from the Stag Field detailing the application of the technique as an effective fieldwide correlation tool. The sandstone reservoirs exhibit mineralogical variation and individual sand packages can be discontinuous. However, the major shale packages are laterally continuous and individual shales show remarkable character consistency over several kilometres. Such character continuity has proved a valuable correlation tool for confirming and refining the stratigraphic packages observed in the Cretaceous section of Stag.

Success on the Stag Field led to application of the technique for regional correlations on the Enderby Terrace. The results of regional work show that correlations still hold when the technique is applied to correlations of over 70 km even though some lateral variation due to provenance and depositional environment impact on clay types was evident. Hence this qualitative approach of wireline log evaluation has proved an effective and valuable correlation tool.