The paper presents the results of a comprehensive petrophysical study of siltstone–sandstone rocks of the Gazsalin member of the Kuznetsov formation of Turonian age. The analysis performed is based on the interpretation of well logging data as well as laboratory core studies from six wells located within three fields of the Russko-Chasel megaswell. It is established that the studied deposits are characterized by pronounced thin bedding, high lithological heterogeneity, and significant clay content, which results in a combination of high porosity and extremely low permeability. It is shown that standard well logging methods have limited vertical resolution when applied to thinly bedded clayey siltstone–sandstone rocks and do not enable reliable estimation of the effective thickness of reservoir laminae. The integration of neutron and density logging data, together with X-ray diffraction analysis of clay minerals, enabled to refine the clay volume model and improve the reliability of porosity calculations. The applicability of the classical Archie model was evaluated, revealing instability of its parameters across different wells. Analysis of core capillary pressure data and residual water distribution, combined with clay mineralogical data, enabled refinement of electrical model parameters, representing an important step toward constructing a reliable petrophysical model of the Turonian deposits.
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