The specificity of the seismogeological correlation of neocomian deposits of different facial regions of the Fir-Yugan zone (Uvat district of the Tyumen region)

DOI: 10.24412/2076-6785-2023-8-34-44

Abstract
According to the regional facies zoning of the Neocomian deposits of the West Siberian Basin, the Fir-Yugan zone is located at the junction of two facies regions (FR) – Surgut and Nizhnevartovsk, which are characterized by a different type of section – the number of sand layers and their indexing. In the practice of geological exploration, the first type of section is called “Surgut” and unites a group Iof BS sand layers. The second type of section is called “Vartovsky” and unites a group of BV layers. Due to the difference in structure and facies nature between the types of sections in the undaform part of the Neocomian clinoform reservoirs, in the territories of transition zones today there is a problem of correct geological correlation of isochronous layers of these facies areas. The study of the Neocomian complex of regional and zonal levels is based mainly on seismic phase correlation, therefore, in such territories as the Fir-Yugan zone, there is a problem of correct interdistrict correlation of layers not only according to drilling data, but also according to seismic materials. The article shows the experience of solving this problem for the Fir-Yugan zone.
The features of the facies structure of the “Surgut”, “Vartovsky” and transitional type sections are given. The features of dissection and correlation of neocomial strata in differ-ent facies areas according to drilling data and problems of seismic correlation are presented. For the correct binding of reflected waves for each type of section, an example of synthetic acoustic one-dimensional modeling is given, recommendations are given for taking into account the struc-tural features of each type of section.

Materials and methods
The study used the materials on 20 exploration and appraisal wells with relatively complete data packages: core, well logging, and 3D CDP data within the survey contour. The paper provides examples only for individual wells, illustrating each type of cross-section. The 3D CDP seismic materials on the Keumskaya, Pikhtovaya, Tyamkinskaya, Taltsiyskaya, Protozanovskaya, Urnen-skaya, Yuzhno-Gavrikovskaya, and other areas of the Uvat Area of the Tyumen Region were also used. To analyze the geological material, the sequence-stratigraphic and facies analyses (core/log-based) methods were used. To solve the problem of comparing the boundaries of system tracts and seismic phases of the wave field, the following methods were used: one-dimensional modeling and acoustic inversion.

Keywords
surgut-type section, Vartovsky-type section, well correlations, Ust-Balyk Series, Sortym Series, Vandensky Series