Reservoir Develoment Within The Waarre Formation, Port Campbell Embayment, Onshore Otway Basin, Victoria.
Trupp, Mark Andrew
Honours Degree, 1988
University of Adelaide
The Waarre Formation is the reservoir for several small but economic gas fields in the Port Campbell Embayment of the Otway Basin. It was deposited as the first sediments on the unconformity associated with the mid-Cretaceous break-up of East Gondwanaland. The Waarre Formation contains both excellent and poor reservoir quality sandstones. Development of a depositional model and study of the diagenetic controls on reservoir development permits the distribution of the high quality reservoirs to be predicted.
Detailed study of wireline log character, lithological and sedimentological descriptions (from cores and cuttings), along with the study of petrology and interpreted provenance, mineralogy, and biostratigraphy allowed the formulation of a depositional model for the Waarre Formation.
Fluvial, immature, sands were deposited on a broad alluvial plain which was subsequently inundated by tidal dominated shoreline sediments. This transgression was halted by a major fall in sea level producing widespread subaerial exposure with possible valley incision. Fluvial deposition was concentrated along this incised valley system. Thickening across faults indicates structural control on deposition. Continued transgression blanketed the Waarre Formation with a laterally extensive marine siltstone/shale seal.
Study of the porosity characteristics and diagenesis places depositional and burial constraints on the distribution of the high quality reservoirs. The upper fluvial sequence is the prime reservoir objective. Deposition of clean fluvial sands, along with a lack of porosity reduction during burial results in excellent reservoir properties. The distribution of this upper unit is predicted, along with that of the secondary objective, the underlying transgressive barrier sequence.