Reservoir quality evaluation using petrophysical, well-log analysis and petrographical description: A case study from the Carboniferous-Permian Kulshill group formations, southern Bonaparte Basin, Australia

Abstract

The Carboniferous – Permian Kulshill Group formations are producing reservoirs in the Petrel subbasin, Australia. The studied Keyling and Kuriyippi formations were investigated by integrating petrophysical, petrographical, sedimentological, and well-log interpretations. The petrophysical study reveals that both formations Keyling and Kuriyippi have very good porosity (max. 30.9% and 25.2% respectively) and permeability values (max. 3053 mD and 1025 mD respectively) indicating good reservoir quality. Based on petrographic descriptions, both formations comprise very fine to coarse-grained sandstone and moderate to well-sorted with abundant intergranular porosity. Many diagenetic factors acting on the reservoir quality of the Kulshill Group formations are observed. Cementation and clay minerals as well as secondary porosity is more visible in both formations while at the same time the formations still holding good enough reservoir quality. The interpreted well-log data indicate that the Kuriyippi Formation is mostly oil bearing, whereas the Keyling Formation is water bearing reservoir. The average petrophysical parameters of both formations show that porosity values reaching up to 16.5–32.3% respectively, and clay volume up to 25.2% with abundance of montmorillonite, mixed clay layers, while glauconite, micas, and illites were found in few amounts in both formations. The hydrocarbon saturation recorded higher values (up to 80.4%) in the Kuriyippi Formation while the measured values in the Keyling Formation is less and the water saturation is always playing around the cutoff values. This can be attributed to the presence of the permeability barrier Treasury shale Formation underlying the high quality Keyling sandstone reservoir blocking the upward migration of hydrocarbon.