DETERMINATION OF RESERVOIR DISTRIBUTION OVER THE BLACKBACK/TERAKIHI OIL FIELD, GIPPSLAND BASIN, AUSTRALIA

Abstract

The Blackback/Terakihi oil accumulation is located within the Gippsland Basin permit Vic-P24 on the edge of the present-day continental shelf in water depths ranging from 300 to more than 600 m. Accurate structural mapping, depth conversion and delineation of the reservoir units remain as major uncertainties associated with this oil and gas accumulation. To date three wells, Hapuku-1, Blackback-1 and Terakihi-1 have been drilled on the structure and a 3D seismic survey interpreted.

The top of the Latrobe Group structure is a complex erosional remnant somewhat laterally offset from a deep-seated northeast to southwest trending, faulted anticline. Most of the hydrocarbons intersected to date have been encountered within the top of the Latrobe Group closure. All three wells drilled to date have intersected oil at the top of the Latrobe Group in three markedly different reservoir units. These reservoirs range in age from Late Cretaceous to Eocene, with porosity ranging from less than 12 per cent to 26 per cent and permeability from less than 1 md to greater than 3000 md.

Given the extreme variation in reservoir quality and the field's location in relatively deep water, delineating the distribution of reservoir units using all available data remains crucial.

The generation of seismic attribute maps such as dip, dip azimuth and horizon amplitude slices, calibrated on existing well penetrations has played a major role in delineating a complex reservoir distribution at the top of the Latrobe Group. The calibration of high amplitude seismic events with a high impedance channel infill unit of Eocene age was supported by modelling using SIERRAR modelling software.

The integration of existing well control, seismic stratigraphy and fault geometry together with seismic attribute mapping and modelling has resulted in a more tightly constrained estimate of the field reserves.