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Predicting hydrocarbon accumulations below deep Permian salt in the Pricaspian Basin; the use of shallow geochemical indicators

The Pricaspian Basin in the southeast of the Russian Platform contains a sedimentary column up to 20 km thick comprising Palaeozoic subsalt formations, Permian salt and suprasalt Mesozoic and Cenozoic terrigenous formations. The huge oil and gas reserves of the Basin are concentrated in subsalt Upper Palaeozoic carbonate reservoirs. Geologists generally agree that the hydrocarbons in the numerous, generally small fields discovered in Mesozoic reservoirs migrated from deeper, subsalt strata. This suggests that traces of fluids at shallow stratigraphic levels may indicate the deep, subsalt sources of the hydrocarbons and associated components. Subsalt reservoirs at depths of more than 6000 m are targets for future exploration. The location of hydrocarbon pools in such reservoirs may be indicated by geochemical investigations of the salt and of the terrigenous rocks above the salt. The distribution of geochemical indicators in the post-salt section may aid the prediction of undiscovered hydrocarbon pools in deep Palaeozoic carbonate formations.