The paper presents the results of the connate water study of the Upper Devonian organo-carbonate shale rocks of the Bym-Kungur Monocline of the Volga-Ural oil and gas-bearing province using an integrated workflow. The workflow was specially developed for low permeable shale rocks. It included the determination of 1) the pore water content (free and loosely bound types) using the Dean – Stark and evaporation methods, 2) the chemically bound water content by the thermogravimetric analysis coupled to differential scanning calorimetry and Fourier transform infrared spectroscopy, 3) the ion-salt complex composition using aqueous extracts, 4) the mineral composition by XRD analysis, 5) the cation exchange capacity (CEC) values by the modified alcoholic ammonium chloride method, 6) the organic matter quality and content by the Rock-Eval pyrolysis and 7) the lithological and petrographic description of rock sections. We studied a set of representative samples of the Sargaev, Domanic and Mendym horizons from one well with the maximum preserved natural water saturation. We found that the rock samples have a high heterogenety of the mineral and organic matter composition. The investigated samples contained residual formation water of 0.03–0.43 wt.%. The amount of chemically bound water are in a range of 0.04–1.02 wt.% and exceeds free and loosely bound water. Average of CEC of studied samples is 5.79 meq/kg and depends on the clay content. The salinity of aqueous extracts from the natural rock samples varies in the range from 0.24 to 0.94 g/L, pH – from 7.81 to 9.08. The chlorine and sodium dominate in the aqueous extract composition. The clay contents and the presence of significant amount of organic matter in the rocks define the variation of the ion-salt complex composition. The obtained results fill the knowledge gaps in the petrophysical interpretation of well logs, as well as general Domanic reservoir characterization and reserves estimation. The research novelty is in using a unique suite of laboratory methods adapted for low permeable carbonate shale rocks with the initial water content of less than 1 wt.%.
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