Rodica Dragomirescu

MSc Student

Telephone: +61 8 8303 4594
Facsimile: +61 8 8303 4345

MSc Project:

Hydrocarbon Seal Evaluation: Nappamerri Group and Cuddapan Formation (Triassic), Cooper Basin, South Australia.

Commenced: 1999

Supervisor: Dr John Kaldi, Dr Nick Lemon, Elinor Alexander (PIRSA)

Project support: Santos Queensland

Scholarship support: Primary Industries and Resources, South Australia (PIRSA)

This study evaluates the seal potential of Triassic rocks in the Cooper Basin, South Australia. It also characterises the major reservoir lithofacies.

Five reservoir lithofacies and four seal lithofacies were identified. Petrographic attributes (composition, texture, diagenesis, cement relationship) of these rocks were integrated with their petrophysical attributes (porosities, permeabilities, pore geometry and capillary pressure analysis) for lithofacies characterisation.

Seal capacity was evaluated using mercury injection capillary pressure (MICP) analyses. The maximum hydrocarbon column heights were calculated for each sealing lithofacies. The sealing lithologies were recognised on wireline logs, correlated and mapped for thickness and quality in wells across the Merrimelia Field. This enabled evaluation of the seal geometry. Seal integrity was qualitatively determined based on petrographic criteria and core description.

The sealing potential of the four lithofacies identified in the study area was ranked. The best sealing potential exists within palaeosols and floodplain mudstones. These lithofacies are thick, have good lateral extent and high measured seal capacities. Although of relatively higher seal capacity and homogeneity, lacustrine mudstones have a lower seal potential because they are thin and distributed only locally. The poorest seal potential occurs within the diagenetically-modified sandstones. This lithofacies is thin, with unpredictable lateral distribution, poor rock mechanical properties and low seal capacity.