The results of exploration of Rosneft’s license areas in the Irkutsk region for 10 years

UDK: 550.81

Key words: Eastern Siberia, Nepsko-Botuobinskaya anteclise, oil reservoir, Ust-Kut horizon, basement, exploration

Authors: Ya.I. Gordeev (Rosneft Oil Company PJSC, A.V. Gaiduk, A.V. Mityukov (RN-Exploration LLC, RF, Moscow), A.V. Filichev (Verkhnechonskneftegas PJSC, RF, Irkutsk)

The article is dedicated to the history of geological exploration carried out by Rosneft Oil Company in Irkutsk region. The article covers key milestones, main problems encountered in the process of geological exploration as well as achieved results. Currently, the Company owns rights to mineral extraction from 10 license blocks. For over 5 years of exploration activities, the Company has booked hydrocarbons reserves produced from several fields, but within the fields of Irkutsk region no natural flow of hydrocarbons have been observed. All the discoveries were associated with tight reserves. Only in 2011 a drilled well showed natural flow of oil from a fundamentally new type of prospects of Ust-Kut horizon, which had not been previously considered as a highly promising. That was a beginning of a new approach in geological exploration - prospecting for better quality reservoir zones among hydrocarbons accumulations associated with tight reserves (the concept of «sweet areas»). Presently, all wells drilled in the prospects identified based on the new concept have been successful (natural flow of hydrocarbons after drilling). High-quality 3D seismic acquisition not only confirmed the available discoveries, but also helped to identify new prospects, including Osinsky horizon and clastic sediments. The article describes how, by changing a geological concept and, therefore, a strategy of geological exploration, the company managed to drill wells with naturally flowing oil and gas, made discoveries with traditional HC reserves and raised a share of successful drilling to 75%.
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