Reservoir quality and diagenesis of the West Erregulla field, North Perth Basin, Western Australia

Abstract

The West Erregulla field is the deepest onshore gas discovery in Australia today, with three wells drilled to more than 5000 m vertical depth. The reservoir quality has been preserved at depth by clay coating, which shows a similar trend with core from other shallower fields in the northern Perth Basin such as Waitsia and Beharra Springs Deep. The primary reservoir in the West Erregulla field is the Permian Kingia Sandstone that was deposited in a tidal estuary environment, which allowed for mixing of meteoric and saline waters. This depositional setting has been inferred from core, image logs and seismic interpretation. This setting resulted in quartz grains coated in chlorite/illite that has limited quartz overgrowth cements and maintained intergranular porosity. This paper presents Strike’s interpretations of the depositional environment that resulted in the anomalous depth–porosity trend based on core analysis, high-resolution borehole image log interpretation and cuttings.