Petrographic Characterisation Of Reservoir Quality Variability In The Elang Formation, Northern Bonaparte Basin.
Forbes, Angus McDonald
Honours Degree, 1998
University of South Australia
The aim of this study was to determine the controls on the reservoir quality of the Elang Formation across permit WA-260-P in the Northern Bonaparte Basin, using the petrographic database of BHP Petroleum and sequence stratigraphy.
The BHP database was extended with twenty three new samples taken for petrographic analysis, which included compositional determination, cathodoluminescence (CL) and X-ray diffraction (XRD). The petrographic analysis showed that most of the samples are quartz to sublithic arenites with four main cements of quartz, pyrite, kaolinite and calcite. The CL analysis and the petrographic textural evidence indicate the carbonate cement occurred early in the diagenetic history of the formation. Minor amounts of quartz cementation are associated with the carbonate cement, but the majority occurred later, possibly associated with increased Tertiary burial. The formation of kaolinite coincided with the later stages of quartz overgrowth and the majority of the pyrite occurred relatively late, associated with hydrocarbon migration.
Within the four main facies sampled, grain size, matrix and carbonate cement abundance display the only significant variations which also affect reservoir quality. A statistical analysis of the data revealed that grain size and matrix might be used as an indicator for proximal and distal depositional environments.
The study has shown that the poorer reservoir quality tends to be associated with the delta slope/lower shoreface facies. The majority of the good reservoir quality can be seen at the top of two overall prograding packages that extend across the WA-260-P. These packages tend not to comply with some of the depositional facies distributions currently used. Some reinterpretation of the sequence stratigraphy may be necessary.