The article is devoted to an urgent issue - the creation of a conceptual model of the structure of the gas-bearing reservoir of the Turonian sediments (reservoir T of the Kuznetsov formation) in the northern regions of Western Siberia. The formation of a geological concept is considered on the example of a gas deposit identified within the boundaries of the Kharampur and Festival deposits in the deposits of the Gazsalinskaya member of the Kuznetsov suite. The uniqueness of the Kharampur field is the presence of gas reserves in the sandy section of the Turonian sediments of the Kuznetsov suite. The presence of siltstone-sandy interlayers in the Kuznetsov suite, allocated to the Gazsalinsky stratum, is a feature of only the Taz type of section. The deposits of the Ghazalinsky member are characterized by reduced reservoir properties and increased clay content compared with the Cenomanian strata of the Pokur formation. A prerequisite for the formation of a new geological concept was the results of the first experimental work at the facility. They revealed low confirmation of the previously approved geological model of the T formation and the sharp ambiguity of the petrophysical and structural parameters. This led to the need to review the entire existing geological concept of the Turonian sediments, including the creation of a new petrophysical base taking into account the heterogeneous reservoir.
Based on the core and well logs, the three-membered structure of the T formation was established, and the conditions of formation of each pack were studied. The complex structure of the T layer is due to the thin interbedding of reservoirs and non-reservoirs, additionally complicated by bioturbation processes. Such structural and textural features lead to an underestimation of the filtration-capacitive properties and complicate the justification of the gas-water contact according to well logging data. The gas saturation coefficient is of greatest difficult to determine. On the basis of the concept of the mixed chemogenic-terrigenous genesis of the deposits of the Ghazalinsky stratum, the author's version of the petrophysical model of a heterogeneous reservoir is proposed. The use of a heterogeneous reservoir model makes it possible to more accurately determine the effective volume and reservoir properties. The main characteristics of the gas-bearing reservoir were also studied: modern and paleomorphology of the Turonian deposits, tectonophysical characteristics of the morphostructure of the region, the prevailing directions of modern and paleostresses, the nature of the manifestation of disjunctive tectonics.
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