Thermal properties of the bituminous sandy rocks of the Volga-Ural oil and gas province.

Abstract

Natural accumulations of bitumen in the Volga-Ural oil and gas province are unconventional sources of hydrocarbons. They are mainly concentrated in the Republic of Tatarstan and are confined to psammitic (sandy) rocks of lower Permian age (Sheshmian Horizon of Ufimian Stage). Sands and sandstones belong to the greywacke group, so rock-forming minerals are represented by quartz, feldspars and effusive fragments. The internal structure of the bitumen-containing reservoir is characterized by an extreme degree of lithological and mineralogical heterogeneity, which is the result of the imposition of a whole complex of processes. Since the beginning of the development of bitumen deposits by thermal methods, the issues of studying the internal heterogeneity and its influence on the production process become particularly acute. Internal reservoir heterogeneity may prevent uniform heating and the formation of a full-fledged steam chamber. Sands and sandstones of the productive part are divided into three rock types (bituminous sands, bituminous sandstones and residual bituminous sandstones). Thermal studies using methods of thermogravimetry (TG) and differential scanning calorimetry (DSC) showed differences in rock types in terms of the decomposition of mineral and organic components, as well as the removal of gaseous components. As a result of thermal studies, it was found that not only loose, bitumen-saturated sands, but also denser, cemented rock types can serve as a reservoir for hydrocarbons. This is due to the conservation of hydrocarbon fractions in the intergranular space during the formation of carbonate cement.