Distribution of organic matter in rocks of the Bazhenov horizon (West Siberia)

Abstract

We studied the distribution of organic carbon in rocks of the Bazhenov horizon, a unique object of predominantly biogenic sedimentation in the West Siberian sedimentary basin. The contents of organic carbon in the rocks were determined using the data from 4094 core analyses and core-log relationships derived from 48,500 radioactive- and electrical-log measurements. For the Bazhenov and Tutleima Formations, both approaches gave the same results. The average content of organic carbon in the rocks is 7.7%. These data were used to compile a detailed map of the distribution of organic carbon contents in sedimentary rocks of the basin. It was shown that the average organic carbon content in the rocks increases from 2–4% on the periphery of the basin to 10–12% in its central, deepest part. The distribution of Corg values in the basin is highly asymmetric. The highest Corg values are observed in the southwestern part of the basin interior, where beds with > 10% Corg range in thickness from 5 to 12–15 m. In sections, the highest Corg values are observed in their middle and upper parts, composed predominantly of silicites and mixtites enriched in biogenic silica.

Alginite-Rich Layers in the Bazhenov Deposits of Western Siberia

“…The total organic carbon (TOC) concentrations vary considerably from less than 1 up to 30 wt.% for different lithological units within a cross-section. The TOC variations are usually accompanied by considerable variations of the hydrogen index (HI), chemical and isotope composition, and level of organic matter thermal maturation [1][2][3][4]. These variations reflect the changes in sedimentation conditions, including the rate of sedimentation, diversity of marine biota and bioproductivity, redox conditions, and others [5][6][7].…”

Raw material base of Russia’s unconventional oil and gas reserves (hydrocarbons shale strata)

“…A specific feature of high-bituminous strata enriched with organic carbon the ability to generate and preserve generated hydrocarbons within single strata or in low-permeable boundary strata associated with it above and below the section (Neruchev, 1962;Neruchev and Smirnov, 2007;Bazhenova et al, 2008;Kiryukhina et al, 2013a;Bazhenova and Dakhnova, 2014;Sannikova et al, 2017;Kontorovich et al, 2018). If there are high-quality screening layers above and below the horizon, the reservoir properties of rocks are "preserved" and deposits of the traditional type are formed in the Domanikoid at the generation site, often with abnormal high pressure (for example, the Salymskoye field in Western Siberia).…”

“…The diameter of the voids of dissolution of radiolarian skeletons reaches 100 microns, the length is 250 microns, and some of these voids can later be partially or completely dolomitized. They were determined using an electron microscope (Kontorovich et al, 2018). In addition to micro-…”

“…Large-scale studies of recent years (Rogozina, 1983;Kiryukhina et al, 2013b;Varlamov et al, 2020) have estimated the distribution of OM in rocks of the Bazhenov formation in Western Siberia, reconstruct its content at the beginning of catagenesis, and thus more reasonably approach the problem of estimating residual and non-migrated mobile hydrocarbons (Bazhenova and Dakhnova, 2014;Kontorovich et al, 2018). The potential of the Bazhenov formation according to these studies is estimated to be even higher than the Energy Information Administration estimates and amount to 25 billion tons of recoverable oil resources with a recovery factor of 0.03.…”

“…In 1986, in the work of Neruchev (Maksimova, 1970), all high-carbon oil and gas source formations common in Russia were considered and were combined under the general term "Domanik-type deposits", containing sapropel-type OM. At the head of the school, which studied "Domanik-type deposits", the conditions for the formation of hydrocarbon systems within the sedimentary basins of Western Siberia, the Volga-Urals, and the Timan-Pechora were investigated (Kontorovich et al, 1967;Vassoevich, 1968;Kontorovich et al, 1975;Gurari, 1980;Rogozina, 1983;Bazhenova, 1994;Kontorovich et al, 1997;Bazhenova and Dakhnova, 2014).…”