THE PETROLEUM POTENTIAL OF THE EASTERN ARROWIE BASIN AND FROME EMBAYMENT

Abstract

The eastern Arrowie Basin is a descriptive term for the present-day structurally defined Cambro- Ordovician basin approximately coinciding with the Curnamona Shelf depositional feature which formed on the eastern stable flank of the Adelaide Trough. Remnants of the Arrowie depositional basin are preserved in outcrops of the Flinders Ranges and in the subsurface to the east and west of the ranges. The eastern subsurface sub-basin occupies the area around Lake Frome in South Australia and across the border in New South Wales. Much of the eastern sub-basin is overlain by the Jurassic and Cretaceous rocks of the Frome Embayment of the Eromanga Basin.

The area has been explored sporadically over at least the past 20 years but no deep wells have been drilled to test exploration targets. This assessment of the prospectivity of the basin is assisted by shallow stratigraphic and mineral drilling, by extrapolation from outcrop, and by regional geophysics.

In the deepest part of the eastern sub-basin the total thickness of the Cambro-Ordovician sediments is expected to exceed 2500 m. Potential reservoirs can be expected within both carbonate and sandstone rocks. Good secondary porosity exists in sandstones of the Middle to Late Cambrian Lake Frome Group and good porosity development is predicted within possible ooid shoal deposits.

Source material has been demonstrated in outcrop samples with Total Organic Carbon measured at up to 0.35 per cent. It is suggested that petroleum generation probably occurred in Cambrian sediments in the Adelaide Trough (now the area of the Flinders Ranges) and the petroleum migrated east and west to the stable shelf areas. Sufficient depth of burial may also have been attained on the Curnamona Shelf to allow local generation.

In the past, the very poor quality of available seismic data has frustrated the mapping of the subsurface in sufficient detail to justify exploration drilling. Recent experimental seismic surveys, however, have produced data of a much better quality. Potential exists for anticlinal, fault and unconformity traps. There is also some potential for stratigraphic traps such as ooid shoal deposits. At this stage an exploration programme to evaluate the potential of this area is being carried out by the licence holders.