MODELLING OF PHANEROZOIC FOCI OF HYDROCARBON GENERATION TO ASSESS THEIR ROLE IN FORMATION OF THE PALEOZOIC OIL DEPOSITS (SOUTHEASTERN OF WESTERN SIBERIA)

Abstract

The relevance. Commercially producible volumes of oil and gas from the Paleozoic play are defined within all territory of Western Siberia. Extensive work to assess the amount of the pre-Jurassic hydrocarbon resources was performed in southeastern. There 13 hydrocarbon deposits were discovered in calcareous, siliceous and clayey, sandy and gravelite rocks. These objects are relegated to hard-to-recover resources, but at the same time are regarded as investment attractive in the reason of location in territories of oil fields with well-developed infrastructure. This study states and solves the issue concerning modelling of the Mesozoic and the Paleozoic catagenic foci of hydrocarbon generation and performs the assessment of their role in formation of the Paleozoic oil deposits. The main aim of the research is to assess the role of the Phanerozoic foci of hydrocarbon generation in formation of the Paleozoic oil deposits. Objects. This paper involves setting and solving the issue regarding to paleotectonic and paleotemperature reconstructions of the Paleozoic and the Mesozoic foci of hydrocarbon generation in the section of the Gerasimov oil-gas condensate field, which is located within the Ostanino group of fields in Tomsk region. Reservoirs of the weathered and the inner Paleozoic – Lower Carboniferous Kehoreg suite are occasioned with epigenetic processes in old weathering crust in period of 213–208 Ma ago. Database on the field includes well test temperatures and vitrinite reflectance data both as from the Jurassic, so from the pre-Jurassic sections and also documented information about fluid inflows from the pre-Jurassic play. Methods. Paleoreconstruction is carried out by paleotemperature modelling method. The applied model does not require making final calibrations with vitrinite reflectance data. Deep heat flow is determined by solving inverse problem of Geothermy using proprietary approach including two steps. The first step involves density estimation of the quasistationary heat flow associated with the beginning of the Jurassic period. The second step intends to determine heat flow value in the Silurian and its dynamics until the Early Jurassic. Depositional and thermal history of the Phanerozoic source rocks (the Paleozoic formations: Larin, Mir, Chuzik, Chagin, Kehoreg; and the Jurassic formations: Tyumen, Bazhenov) is restored by solving direct problems of Geothermy. Results. Co-generating sources of hydrocarbon deposits in the weathered and the inner Paleozoic were defined and studied as a result of performing coupled paleotemperature modelling of the Phanerozoic foci of hydrocarbon generation in the Mesozoic and the Paleozoic sedimentary basins. Accountancy of succession of generation and oil and gas migration, timeframe of reservoirs formation, oil origin analysis data allows identifying oil from the Paleozoic reservoirs as Bazhenov oil. Domanic rocks of Kehoreg suite are accepted as a gas source for Paleozoic reservoirs. The conclusion. Paleotemperature study of the Gerasimov field section and modelling within the Selveikin area of deep drilling and the Ostanino field performed earlier show that two alternative concepts of the main source for the Paleozoic hydrocarbon deposits are not mutually exclusive. It seems that for the Paleozoic deposits an oil source rock, more likely, is the Upper Jurassic Bazhenov formation and a gas source rock (for generating gas and condensate) is the Paleozoic domanic rocks.

Keywords

• paleozoic oil and gas play
• phanerozoic hydrocarbon sources
• paleotemperature modelling of foci of hydrocarbon generation
• co-generating sources of the paleozoic oil
• the ostanino field group in tomsk region