Halogens in Pore Water of Tight Rocks of the Bazhenov Formation in the Nizhnevartovsk Arch of Western Siberia, Russian Federation

The paper presents data on halogens content (Br⁻, Cl⁻ and I⁻) in pore water of tight rocks of the Bazhenov Formation (BF) in the Nizhnevartovsk arch of Western Siberia, Russian Federation. We used an integrated approach to analyze 7 whole core samples with the maximum preserved natural water content from 2 different BF fields. Here for the first time, we show that the aqueous extract method can be used to estimate the iodine content in pore water of shale rocks. The target BF rock samples contain silicate minerals, clays, carbonates, pyrite, plagioclase, feldspar, have a high mass content of total organic carbon 5.99÷12.00 wt.%. The residual water content for all studied samples changes from 0.76 to 3.89 wt.%. We found that the Cl⁻ content in pore water varies from 1.4 to 14.2 g/l, Br⁻ from 1.58 to 36.99 mg/l and I⁻ from 2.93 to 36.11 mg/l. I⁻ and Br⁻ concentration in BF pore water is much higher than in seawater. The content of halogens varies unevenly with the well depth due to heterogeneity of the mineral composition of BF rocks even within one well. We discovered that the organic matter of BF almost completely releases the iodine in the pore solution due to diagenesis and katogenesis processes. All target BF samples have iodine in pore water, and only three BF samples have iodine in organomineral complex of rocks (1-3% of the total iodine content). The obtained results have a great importance because allow expanding the available data on the composition of pore waters in shale rocks of the Bazhenov Formation.