Re-discovering the Gummy gas field – Gippsland Basin

Abstract

Recent sub-surface studies of the Gummy Gas Field have resulted in a significant upgrade of its gas and liquids resource potential. Previous interpretations had ascribed little resource potential to the field. Shell drilled Gummy-1 in 1990, a Golden Beach (GB) Subgroup gas/liquids discovery in the eastern Gippsland Basin. The GB Subgroup was previously described as a stacked, grading to generally thin, isolated sandstone reservoir hosting limited gas volumes. In 2022, a new study integrated the interpretation of the CGG Gippsland Multi-Client 3D seismic survey dataset with a re-look at the reservoir characterisation, petrophysical properties and reservoir pressures and found that reservoir quality is better than previously thought. The improved reservoir quality is interpreted to be the result of depositional reworking, which also increases confidence that the sandstones are laterally extensive. Consideration of the impact of regional pressure depletion due to nearby production from the GBJV fields has improved the understanding of the hydrocarbon columns encountered at Gummy-1. Increased hydrocarbon column heights are interpreted, which are consistent with wireline log evaluation and regional saturation-height data. Confidence that the seal at Gummy is working as effectively or better than offset fields and reservoirs is high. The new interpretation has also significantly improved the exploration potential for underlying gas reservoirs within the middle and lower GB Subgroup. Gummy-1 reached a total depth of 3530 m MDRT in a gas sandstone reservoir with an interpreted main gas column up to 185 m. Potential exists for additional gas in reservoir quality sandstones to be discovered in deeper exploration targets – the Gummy Deep exploration prospect. Combined with the adjacent Manta Gas Field, this demonstrates the enhanced potential for future commercial development in the area.