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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]

One of the productive horizons (17th) of north Sakhalin has been studied. The areas within and beyond oil and gas pools, near the top and at the flanks of structures were compared with areas where the horizon under study was water-bearing. The rocks were least transformed by secondary processes within oil accumulations, where a sudden increase was observed in the content of feldspars and accessory minerals (epidote, ilmenite and sphene) which had not undergone intrastratal solution. Inside gas pools, however, no deceleration of epigenesis has been observed. This points to a more recent (post-Pliocene) accumulation of gas, whereas the first oil migration in these Miocene strata occurred in the Upper Pliocene, according to the hampered epigenesis. [ABSTRACT FROM AUTHOR]

The paper presents the dynamics of the structural change of kaolinite and its polymorphous (polytype) modifications at different stages of sedimentary rock formation. Sedimentogenesis is characterized by a gradual disordering of structure of triclinic kaolinite, the degree of disorder produced being proportional to the intensity and duration of the influence of the hydrodynamic medium. Epigenesis (deep) is connected with gradual transformation of kaolinite into dickite through the stage of mixed-layer growths inheriting the structure of twin rotations of disordered kaolinite from the sedimentogenesis stage. In metagenesis filling of fissures with dickite or nacrite takes place. The former is peculiar to the general thermodynamic medium of deep epigenesis/metagenesis, whereas nacrite is an indicator of intense stress and seems to be due to transformation of dickite. [ABSTRACT FROM AUTHOR]