Salinity and Macrocomponent Composition of Pore Water of the Bazhenov, Achimov, and Georgiev Formations from Analysis of Aqueous Extracts

Abstract

This paper presents a reliable dataset on formation water salinity (mineralization) and salt composition for low-permeable (tight) shale rocks of the Bazhenov, Achimov and Georgiev formations for the first time. The data were obtained via laboratory analysis of aqueous extracts from rock samples before and after hydrocarbon extraction (cleaning). Thermodynamic modeling of the obtained solutions with a number of minerals was carried out and a correlation analysis of the Na/Cl, Ca/SO₄, Mg/SO₄, Ca/Cl, Ca/HCO₃, and Fe/SO₄ ratios was performed. It was established that the concentrations of certain macro-components, including Ca, Mg, Fe, hydrocarbonate, and sulfate ion in pore water cannot be reliably determined using aqueous-extract data, while at the same time, a reliable estimate of the minimal formation water salinity could be made. The need to use non-extracted core samples with the maximum preserved residual water saturation to study a pore water composition of tight shale rocks is shown.