Comprehensive studies of pore water of Achimov formation using archived cores

UDK: 553.98:556.31

DOI: 10.24887/0028-2448-2025-6-34-39

Key words: Achimov formation, water saturation, dry core sample, evaporation method, cation exchange capacity (CEC), salinity, aqueous extracts

Authors: E.S. Kazak (Lomonosov Moscow State University, RF, Moscow); N.V. Morozov (Gazprom Neft Companу Group, RF, Saint Petersburg); E.A. Bakay (Lomonosov Moscow State University, RF, Moscow)

The paper presents the first investigation results of the pore water content and chemical composition of the old/dry/archived core samples of the Achimov Formation (ACh). The studied materials include ACh rock samples from 12 fields, gathered more than 10 years ago at the geologic exploration stage. To study pore water composition and quantitative content, the previously proposed integrated approach with proven effectiveness in fresh low-permeability rocks was used. Despite the low permeability, the authors found that the ACh rock samples during storage lost almost all (up to 90 %) free water due to evaporation. Nevertheless, salts from formation water remained in the pore space, which enabled to estimate the range of the NaCl salinity (1,84–14,7 g/L). The obtained values set the lower limit of the possible pore water salinity of the studied ACh rock samples and match those from direct salinity measurements in the ACh depth intervals. The cation exchange capacity (CEC) range of the studied ACh rock samples is 3,13–3,95 meq/100 g of rock and is typical for sediments at the considered depths. It is shown that the old/dry/archived ACh core could be effectively used to assess the bound water content with subsequent determination of its genesis from isotopic composition data and CEC measurements. This is due to the high clay content (44,6–55,8 %) in the studied ACh rock samples. The obtained results show the fundamental capability of informative laboratory studies of rock samples from public and private core storage facilities.

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