Impact of paragenesis on the quality of a mixed carbonate-siliciclastic reservoir from the Perth Basin, Australia

This research focuses on the Beekeeper Formation, a mixed carbonate-siliciclastic (MCS) reservoir in Western Australia. MCS reservoirs are proven to contain hydrocarbons in many fields worldwide. The importance of this type of reservoir, however, is not well addressed, and much is not known about the impact of paragenesis on the quality of this type of reservoir. There are two objectives of this study: (1) to unravel the main paragenetic events of the Beekeeper Formation, its abundance, and relative timing; and (2) to better understand the impact of paragenesis on the quality of a MCS reservoir. Integrated geological analyses, including sedimentary logging, standard thin section, cathodoluminescence, and fracture system analyses have been conducted to achieve the objectives of this study. Detailed description, and interpretation of each paragenetic events of the Beekeeper Formation is provided in this study. Moreover, the results show that mechanical compaction, syntaxial overgrowth, and cementation are the main paragenetic events that decreased the porosity of the Beekeeper Formation. While fracturing, dolomitisation, dissolution of bioclast, and calcite veins are the principal forms of the diagenesis that lead to an increase in pores. Four types of pores were identified from this study: fracture, vug, intergranular, and intercrystalline pores of dolostone. The fractures provide the highest pore systems quality within the Beekeeper Formation, and then followed by the intercrystalline pores of dolostone, and vugs. The intergranular pores is of low quality. These secondary pores provide migration pathways for hydrocarbon, and thus compensated the lack of primary porosity. Findings from this study provide insights into the main influences on the quality of a MCS reservoir, and can be applied as an analogue study to similar formations worldwide.