Lithology of bituminous sandstones of Ashalchinskoye deposit, South Tatar arch

Abstract

Introduction: the development of bitumen deposits in sandy strata using the method of steam-assisted gravity drainage is accompanied by unpredictable circulation of high-temperature fluids due to the complex distribution of permeable and impermeable zones in rocks. The applied task is to determine the causes and features of internal heterogeneity in bitumen deposits based on the lithological and granulometric characteristics of productive strata. The object of the study is Ufimian (Lower Permian) sandstones of the Ashalchinskoye bitumen deposit in the Republic of Tatarstan.

Methodology: granulometric analysis data on bituminous sandstones of the Ashalchinskoye deposit were processed using methods of basic and multivariate mathematical statistics in the STATISTICA 10 software. Optical and electron microscopy and X-ray computed microtomography were used to study the hollow-pore space.

Results and discussion: the studied sandstones belong to the quartz graywacke group. In addition to quartz, they contain feldspars, micas, pyroxenes, amphiboles, as well as fragments of igneous rocks of the Ural Mountains, which are cemented by carbonate and bitumen matter. The predominant fraction of sandstones is fine-grained (0.25-0.1 mm), which is also the most bitumen-saturated. The results of cluster and factor analysis made it possible to identify “bituminous” and “lithological” groups of granulometric parameters. According to microtomography data, it was established that pores with a volume of less than 0.01 mm³ predominate in sandstones.

Conclusion: the degree of bitumen saturation of the Sheshmian sandstones is associated with their granulometric composition. The content of bitumen substance over 10 % is specific for fine-grained varieties with a particle size of 0.25-0.1 mm. Low carbonate content of sandstones is one of the factors in the prospects for developing bitumen deposits using the steam-assisted gravity drainage method.