Daria Yu. Kalacheva

In this paper, based on a geochemical study of rock samples and fluids, it is proven that carbon-bearing deposits of the Lower and Middle Jurassic complex of Western Siberia on the southern outskirts of the Khanty-Mansiysk and Yamalo-Nenets Autonomous Okrug can generate liquid hydrocarbons. It has been established that the oil-generation potential of carbon-bearing deposits depends on the paleogeographic conditions of burial of the organic matter and the enrichment of rocks with macerals of the liptinite group. The complex of studies included pyrolysis of coals, coal-rich shale of Lower and Middle Jurassic rocks, study of maceral composition and measurement of reflectivity indicators, hydrocarbon and isotopic composition of extracts from rocks, as well as study of the composition of oils from the studied area, selected both within the Jurassic and Cretaceous complexes. The studied area is located in the Frolov megadepression and the South Nadym megamonoclise. The result of the research was the identification of significant geochemical characteristics of an additional source of hydrocarbons – coals, coal-rich shale of the Lower and Middle Jurassic, which had not previously been proven on the studied area, the contribution of which to the formation of oil and gas potential was confirmed by the correlation of hydrocarbon and isotopic characteristics of fluids and extracts from source rocks. Сluster and the principal component analysis were used for genetic correlation of extracts and oils. The conclusions obtained from geochemical studies suggest the possible prospects of Lower and Middle Jurassic deposits from the point of view of detecting hydrocarbon accumulations.

Background. Decline of oil and gas traditional reserves pushes companies to explore and involve in production complex reservoirs which results in exploration risks increase. That is why an exploration research has to be integrational and its’ main result has to be determination and decreasing uncertainties. Aim. The aim of this research is the planning of further exploration program within the studied territory, based on the main uncertainties and trends in geological development. Materials and methods. Several types of research methods were applied, including field observation, laboratory analysis and geological desktop studies. The results of petroleum systems modeling is the basis for source rocks maturity prediction, the main stages of hydrocarbons generation — migration and critical moment estimation. It also provided the analysis of migration distance (limits) and geological risks related to it, petroleum saturation prediction for the main plays. Great emphasis was also placed on the search and processing of additional archival data, which made it possible to significantly detail the structural-tectonic framework of the studied area. Results. Consistent progression in field observation, laboratory analysis and geological desktop studies allowed to narrow the range of uncertainties, clarify the chance of geological success (gCOS), plan the further exploration program, and highlight higher-priority license blocks. As a result, more than 60 additional prospects were identified, for each of them both the probabilistic estimation of oil and gas resources and chance of geological success evaluation were made. Moreover, the further exploration program was approved. Conclusions. Therefore, the study allowed to analyse main uncertainties and correct further exploration program on the basis of integrated analysis of geological development history and geological structure of the studied area.

In situ shale or kerogen oil production is a promising approach to developing vast oil shale resources and increasing world energy demand. In this study, cyclic subcritical water injection in oil shale was investigated in laboratory conditions as a method for in situ oil shale retorting. Fifteen non-extracted oil shale samples from Bazhenov Formation in Russia (98 °C and 23.5 MPa reservoir conditions) were hydrothermally treated at 350 °C and in a 25 MPa semi-open system during 50 h in the cyclic regime. The influence of the artificial maturation on geochemical parameters, elastic and microstructural properties was studied. Rock-Eval pyrolysis of non-extracted and extracted oil shale samples before and after hydrothermal exposure and SARA analysis were employed to analyze bitumen and kerogen transformation to mobile hydrocarbons and immobile char. X-ray computed microtomography (XMT) was performed to characterize the microstructural properties of pore space. The results demonstrated significant porosity, specific pore surface area increase, and the appearance of microfractures in organic-rich layers. Acoustic measurements were carried out to estimate the alteration of elastic properties due to hydrothermal treatment. Both Young’s modulus and Poisson’s ratio decreased due to kerogen transformation to heavy oil and bitumen, which remain trapped before further oil and gas generation, and expulsion occurs. Ultimately, a developed kinetic model was applied to match kerogen and bitumen transformation with liquid and gas hydrocarbons production. The nonlinear least-squares optimization problem was solved during the integration of the system of differential equations to match produced hydrocarbons with pyrolysis derived kerogen and bitumen decomposition.