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 terrigene ous formations. The huge oil and gas reserves of the Basin are concent rated in subsalt Upper Palaeozoic carbonate reservoirs. Geologists gen erally agree that the hydrocarbons in the numerous, generally small fi elds discovered in Mesozoic reservoirs migrated from deeper, subsalt s trata. This suggests that traces of fluids at shallow stratigraphic le vels may indicate the deep, subsalt sources of the hydrocarbons and as sociated 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 t he salt and of the terrigeneous rocks above the salt. The distribution of geochemical indicators in the post-salt section may aid the predic tion of undiscovered hydrocarbon pools in deep Palaeozoic carbonate fo rmations.