OIL AND GAS HYDROGEOCHEMISTRY OF THE PRE-JURASSIC DEPOSITS IN THE SOUTHERN AREAS OF OB-IRTYSH INTERFLUVES

Abstract

The relevance of the research is in solving the fundamental and applied problems of hydrogeology and hydrogeochemistry of the pre-Jurassic basement of the West Siberian artesian basin and is of great importance for studying the crust of the platforms and folded belts in general. The uniqueness and complexity of the facility lies in the fact that the West Siberian basin is the largest section of the young platform, under the cover of which the complexes with different age and different geodynamical and hydrogeological characteristics are articulated. Scientific generalizations of the available factual data have not been conducted for more than 30 years! In addition, the relevance of the research is to assess the current state of the water-pressure systems of the pre­Jurassic complexes, and in developing the hydrogeological criteria for their oil and gas content and refinement of the search and exploration of hydrocarbons in the pre-Jurassic base of Western Siberia. The aim of the research is to reveal chemical and gas compound of groundwaters and brines of the pre-Jurassic complexes, to establish the possible genetic types of groundwaters and brines and their spatial distribution; to assess the metamorphic degree of brines in comparison with a hydrogeochemical standards of Siberia. Methods: using the methods of V.A. Sulin, A.A. Kartsev, S.L. Shvartsev, N.M. Kruglikov, V.V. Nelyubin, O.N. Yakovlev, V.M. Matusevich and other researchers to identify the features of geochemistry of groundwater and brines, to establish the genetic type of groundwater and brines, by using the ratio-coefficient of marco- and mirco-compounds such as: Na/rCl, Сl/Br, Ca/Cl, r (HCO3+CO3)/r (Ca+Mg), B/Br, Br/Cl∙10–3, Sr/Cl∙10–3 and others. Using the integrated-coefficient S (by S.L. Shvartsev) and ratio of Ca/Cl, Br/Cl∙10–3, Sr/Cl∙10–3 to estimate the degree of metamorphism of brines. Results. The paper introduces the geochemical studies of groundwaters and brines of the pre-Jurassic sediments in the southern regions of the Ob-Irtysh interfluve. It is established that underground waters and brines with a total mineralization of 4 to 100 g/dm3 of Cl-Na, Cl-Na-Ca and Cl-HCO3-Na composition are developed in the region, with dominance of the first type. Carrying out a retrospective of hydrogeological history and a detailed analysis of hydrogeochemical data it is possible to assume the dominance of sedimentogenic brines in the section and the presence of lithogenic (thermodegradation), ancient infiltrogenic and condensate waters. A combined consideration of the ratio-coefficient (rNa/rCl, Ca/Cl, Br/Cl∙10–3, Sr/Cl∙10–3) with the integrated indicator of brines metamorphism (S) confirms that in this area the brines are at the initial stage of metamorphism of the chemical composition.

Keywords

• Oil and gas hydrogeochemistry
• brine
• genetic type
• metamorphism degree
• Ob-Irtysh interfluve
• Western Siberia.