Выпуск: 7 , Год издания: 1996

Sedimentary rocks of the southwestern part of oil- and gas-bearing Tunguska Basin of Siberian Platform are represented by carbonaceous-evaporite series of Upper Vendian and Lower Cambrian; dolerite sills up to 500 m in thickness are abundant. Elemental sulfur is found in the rocks. Fluid inclusions contain carbon dioxide, hydrogen sulfide, elemental sulfur, carbon sulfide. It is argued, that chemical peculiarities of oil and gas as well as composition of gases, trapped in inclusions of evaporite minerals, are caused by reactions occurring in the sediments - water - hydrocarbons system under the P-T parameters typical of contact metamorphism and catagenesis. Possible reactions are calculated by thermodynamical methods for the various contents of starting materials. 8 reactions of anhydrite with hydrocarbons of methane-octane row are considered. Parameters in contact metamorphism zone are determined as T=400-700 degrees-C, P=600 kbar. Decomposition of sulfides and carbonates (dolomite at 560 degrees-C) produces significant amounts of hydrogen sulfide and carbon dioxide. Mercaptanes appear among hydrocarbons. Anhydrite and hydrocarbons are the most reactive components of the multisystem. When CaSO4 is deficient, CH4, CO₂ and H2S are the major components of gas phase at T exceeding than 100 degrees-C. When CaSO4 is in excess, methane and other hydrocarbon gases are absent in all temperature range of catagenesis and metamorphism. The role of CO₂ increases drastically at T more than 400 degrees-C, therewith concentrations of CH4 decrease. Results of physico-chemical simulation describe adequately compositional peculiarities of naphtides, gases and inclusions in salt.