Home – Home – Jornals – Russian Geology and Geophysics 2001 number 11-12

Based on generalization of 1500 measurements of vitrinite reflectance, deep zoning of organic-matter (OM) catagenesis in Mesozoic deposits has been established, and schemes of catagenesis were constructed for the top and bottom of the Jurassic deposits. The OM catagenesis is within the range of grades PC₃ to MC₃² in the Upper Jurassic deposits and PC₃-AC₃ in the basal Jurassic horizons. Throughout most of the West Siberian megabasin, OM reached the end of mesocatagenesis and apocatagenesis. Regionally, the degree of OM catagenesis of the Jurassic deposits increases from the margins to the central and northern, most buried, areas of the West Siberian megabasin. The level of OM maturity ubiquitously increases with depth, but the rate of these changes varies throughout the area. The highest deep gradient of variations in OM catagenesis was identified in the Yamal and Gydan regions. Depth ranges of the main zone of oil generation (oil window) were determined from vitrinite reflectance values in different petroliferous regions. In the Nadym-Pur region, the main zone of oil generation is identified in the depth range 2.9-3.8 km, in the Pur-Taz region, at 2.8-3.6 km, in the Gydan region, at 2.4-3.3 km, and in the Yamal region, at 2.0-2.8 km. The Jurassic deposits to depths of about 4.0 km have not passed out of the oil window yet and can be of interest for oil and gas exploration. Down the section, the sequences are in the zone of intense gas generation, and, therefore, preservation of only dry and fat gas accumulations is possible at great depths. The same is true for the Triassic and Paleozoic sediments, in which the organic matter underwent significant thermobaric changes (grades MC₃² – AC₃).