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UDC [(552.52+552.57):(550.83+550.84)]:(551.736+551.761/.763)(571.16) THE STRUCTURAL-MATERIAL AND GEOPHYSICAL DESCRIPTION OF ARGILLACEOUS AND CARBONACEOUS ROCKS OF THE NYUROLKA SEDIMENTARY BASIN (TOMSK REGION)
A. V. Ezhova, N. M. Nedolivko
The argillaceous and carbonaceous Permian-Triassic, Jurassic, and Cretaceous rocks of various composition and genesis types were revealed in the terrigenous succession of the southeastern Nyurolka sedimentary basin and described based on lithopetrographic, X-ray diffraction, and geophysical well survey (induced potential logs, apparent resistivity logs, induction, radioactivity, acoustic, and caliper logs). The structural-material composition of the rocks was correlated with their survey-derived geophysical characteristics. The chemogenic clays are residual products of weathering crust (argillaceous structural eluvium): neoeluvium due to dissolution of loose coarsegrained sediments, paraeluvium of siliceous sedimentary rocks, orthoeluvium as effusive rocks are weathered. In the chemogenic clays, as depending on the bedrock composition, there are wide variations in kaolinite, chlorite, and hydromica content as well as a small content of montmorrilonite, quartz, and siderite. The geophysical parameters of the weathering crust argillaceous rocks do not depend on mineralogy and are characterized by a positive SP signature, high specific conductivity and radioactivity. The clays of marine genesis are montmorrilonite-hydromicaceous with chlorite, often with fauna present; the continental clays are hydromica-kaolinic, hydromicaceous, sideritised, with abundant plant remains. In logs, clastic clays expose the same signatures as chemogenic ones. The presence of bituminous matter in the Bazhenov mudstones causes very high specific electrical resistivity and radioactivity, and the occurrence of carbonaceous interlayers results in high neutron gamma-ray figures. The Jurassic coals were formed at the mesocatagenetic stage (MC), i.e. its substages MC1 and MC2 (A.N. Fomin, IPGG SB RAS). The coals display clear geophysical characteristics: high specific electrical resistivity, low radioactivity figures, increase in borehole diameter. The argillaceous occurrences can be revealed by increase in radioactivity; pyritisation causes increased specific electrical conductivity; and carbonaceous interlayers and lenses in the base of sandy bodies hamper determination of the lower boundary of permeable strata (it lies 1.0-1.6 m above the base in radioactivity and acoustic logs, as from resistivity and induction logging data).
Key words: argillaceous, carbonaceous rocks, coals, material composition, geophysical well logging, Permian-Triassic, Jurassic, Cretaceous, the Nyurolka sedimentary basin, oil and gas content.
DOI 10.20403/2078-0575-2016-1-60-70
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