Lithogenesis associated with tectonic and hydrothermal activation: basis for formation of commercial hydrocarbon accumulations

Geodynamic conditions favourable for hydrocarbon accumulation are notable for mandatory combination of catagenetic (regional background) and hydrothermal (local superposed) rock reworking. In terms of energy, it is heating up caused by durable continuous subsidence although strengthened by hydrothermal process triggered by short-term seismotectonic event, i.e., tectonic and hydrothermal activity. The problem is that geologists often disregard a seismotectonic factor, which, in the presence of hot waters sharply increases mass transfer in subsurface. This causes a swift expulsion (migration?) of micro-oil from source rocks, and in favourable conditions - formation of hydrocarbon accumulations. The authors prove that tectonic and hydrothermal activation accompanies structural changes in riftogenic basins. Epigenetic processes accompanying these changes primarily occur under control of heat and mass convective transfer. Gas-liquid inclusions of newly formed minerals, along with the minerals themselves, are indicative of tectonic and hydrothermal phenomena. The mobility of gas-liquid hydrocarbons during expulsion and lateral migration depends, first of all, on the intensity of superposed tectonic and hydrothermal impact. The intensity index of this impact is equal to the ratio of maximum paleotemperature of homogenization to paleotemperature calculated from vitrinite reflectance. This index estimated for the same intervals of geological section characterises the level of paleothermal mismatch of the natural system. The index can be used in prediction of hydrocarbon occurrence in certain territory. In the promising riftogenic areas where source rocks have reached the temperature zone 80-160 °С owing to conductive heating, values of paleothermal mismatch range (approximately) from 1.4 to 2.3