Proceedings of GIA
CONDITIONS OF HYDROCARBON PRESERVATION IN THE SOUTH CASPIAN BASIN
The paper summarizes all conducted up to the present fragmentary studies, that in one way or another consider conditions of hydrocarbon (HC) preservation in the South Caspian Basin (SCB). The principal factors determining quantitative and qualitative character of destruction of HC accumulations can be categorized as a complex of mechanical, physical, chemical and biochemical processes. The importance of each factor / process in preservation of HC accumulations in the SCB is considered separately. The most intense destruction of oil accumulations is noted in the areas where fluid flows are dynamic, conditioned by tectonic disturbances and mud volcanism. Preservation of HC accumulations has been established to become higher with depth, which is reflected in increase of gas component of HC pools (gas factor). In the SCB heavy degasation is characteristic of structures subjected to the highest elevation and erosion. The studies conducted allow us to state that hypergene alteration of oils in the SCB, both geochemical and biochemical one, are observed down to about 2 km. Some 70% of HC fields in the SCB, in one way or another are located in oil oxidation or biodegradation zone, with their confinement to the basinal flanks. Bottomhole temperatures taken in accordance with technical requirements and their extrapolation allowed making with certain degree of likelihood assessment of critical depth of existence of liquid HCs in the SCB. This depth interval, corresponding to critical temperature level of 175-200°С, occurs at 11,5-13,5 km.