DETERMINATION OF THE TIME OF OIL AND GAS ACCUMULATION BY EPIGENESIS STUDIES.

The paper describes a method for determining the time of formation of oil and gas accumulations on the basis of the number of epigenetic minerals contained in granular reservoir rocks. The beginning of the accumulation is established by comparing the epigenesis state in the oil- or gas-bearing crest areas of the trap with the water-bearing part of the reservoir at different depths of the geological section. This takes into account that the epigenetic processes tend to intensify with depth and to slow down after the rocks become filled with hydrocarbons. The time of accumulation completion is found by comparing the degree of epigenetic alteration of the oil- and gas-bearing reservoirs with the water-bearing reservoirs occurring at the oil (gas)-water interface in the trap. The greater the differences, the older is the age of the pool completion. Lack of a difference indicates a youthful pool completion. In this paper, the ratio of detrital to authigenic titanium minerals, the quantity of regenerated quartz grains, and the pelitization of feldspars have been used. The application of this method is exemplified by oil deposits occurring in the productive Valangien and Hauterive beds (Lower Cretaceous) of the Ust-Balyk and Megion fields of western Siberia. [ABSTRACT FROM AUTHOR]