AN EXPERIMENT IN SOIL GEOCHEMICAL PROSPECTING FOR PETROLEUM, DELLA GAS FIELD, COOPER BASIN

Abstract

The aim of the experiment was to test the method of prospecting for petroleum by soil geochemical analysis of hydrocarbons and, in particular, its possible application in the Cooper Basin. Some 379 samples were taken in traverses across the Della Gas Field and a nearby, undrilled anticlinal structure. The samples were taken from a depth of 5 m at a spacing of 5 per mile (approximately 1 every 300 m). Hydrocarbons were extracted with 2N HCI and analysed by gas chromatography. Some modifications to the published analytical techniques had to be made to overcome the prbblem of traces of organic compounds present in local waters and reagents.

Arithmetic mean values analysed for the Della Gas Field were: acid soluble material, 8.62 per cent; ethane, 1.33 ppm; propane, 0.77 ppm; butane, 0.62 ppm; pentane, 0.84 ppm. In plots of, firstly, the sum of ethane, propane, butane and pentane and secondly that sum normalized to the amount of acid soluble material, anomalous areas containing only a few sample points occur above and near the Della Field, and the undrilled structure.

There is only low statistical correlation between the amount of acid soluble material and the hydrocarbon content of the soils. The hydrocarbon content of the soils may possibly be associated with diagenetic gypsum and calcite and possibly smectite (?mixed layer clay) but the evidence is inconclusive. The soil hydrocarbon content shows some tendency to correlate with the finer grain sizes. The anomalies appear to bear no relation to the vegetation. A radiometric survey with a gamma ray spectrometer showed little variation of values and no relation to the geochemistry nor the outline of the Della Gas Field.

The experiment has shown that significant variations in hydrocarbon content of the soils can be analysed in the Cooper Basin and apparent anomalous zones can be outlined. The anomalous zones may be related to the Della Gas Field.