FOCI OF HYDROCARBON GENERATION AND THE «PALEOZOIC» OIL DEPOSITS IN THE URMAN FIELD (TOMSK REGION)

Abstract

Link for citation: Krutenko M.F., Isaev V.I., Korzhov Yu.V., Osipova E.N. Foci of hydrocarbon generation and the «Paleozoic» oil deposits in the Urman field (Tomsk Region). Bulletin of the Tomsk Polytechnic University. Geo Аssets Engineering, 2023, vol. 334, no. 9, рр. 49-62. In Rus. The relevance. Large oil and gas fields are discovered in the oldest basins on many continents of the Earth. According to some estimates, ~40 % in the total proved oil and gas reserves in the world were distributed in the superdeep strata. Also, the Nyurol sedimentary basin draws a lot of interest in prospects for oil and gas potential in the Paleozoic. The perspectivity of the basin is proved by a large amount of hydrocarbon deposits in the Paleozoic discovered there, numerous oil and gas inflows. This research aims to find approaches to identify the source rocks for the pre-Jurassic hydrocarbon deposits. The main aim: estimation of the Phanerozoic rocks opportunity to generate hydrocarbons accumulated in the pre-Jurassic traps. Objects. This paper presents the results of paleotemperature modelling of the Paleozoic and Mesozoic foci of hydrocarbon generation in the Urman oil-gas-condensate field in Tomsk Region. The Urman field is included into the Chuzic-Chizhapka group of fields. The research is performed for two wells – Urman 5 and Yuzhno-Urman 1. Actual well data include well tests measurements and vitrinite reflectance determinations as in the Jurassic, so in the pre-Jurassic rocks, also recorded fluid inflows from the pre-Jurassic play. Methods. The research is based on applying paleotemperature modelling as the main research method. Paleotemperature modelling is associated with paleotectonic reconstructions and is performed in two steps. In the first step, present-day deep heat flow is determined by solving the inverse problem of Geothermics using formation temperatures. In the second step, maximum deep heat flow associated with mantle plume activation is determined applying vitrinite reflectance measurements in the pre-Jurassic rocks. Dynamics of deep heat flow is reconstructed since the Late Ordovician. As a result of solving the direct problem of Geothermics, we set thermal history of the Jurassic and pre-Jurassic oil-source rocks. Results of paleotemperature modelling for the Urman field allowed identifying possible oil-source rocks for deposits in the pre-Jurassic play. Favourable paleotemperature regime for oil generation in sedimentary sequence of both wells existed only in the Jurassic formations: Bazhenov, Tyumen and Togur. Favourable paleotemperature regime for gas generation existed only in the Paleozoic oil-source formations: in Urman 5 well – in the Late Devonian Luginetsk formation, in Yuzhno-Urman 1 – in the Early Devonian Kyshtovsk formation. The conclusion. The Paleozoic reservoirs of the Urman field accumulate partially preserved gas generated by the Paleozoic source-rocks (Kyshtovsk and Luginetsk) and oil representing a mixture of the Jurassic oil of marine (Bazhenov) and terrigenous (Togur and/or Tyumen) origin.