Unconventional oil accumulations in the Upper Jurassic Bazhenov black shale formation, West Siberian Basin: A self-sourced reservoir system

The Upper Jurassic Bazhenov Formation in the central West Siberian Basin is a classic marine black shale unit containing abundant Type II kerogen with high oil-generation potential. These shales source around 90% of the oil in the West Siberian Basin. They also contain oil accumulations in unconventional self-sourced reservoirs. Reservoir zones are generally small and are located along fault planes. Primary oil migration was focused along fracture networks adjacent to the fault zones. Oil charging took place in the Tertiary and oil generation and expulsion in the Bazhenov Formation led to over pressuring. In the study area between the Surgut and Ayalinsk arches in the centre of the basin, faulting and fracturing took place in Eocene to Quaternary time. The faulting led to local increases in the thermal maturity of the Bazhenov Formation. Exploration risk in the self-sourced Bazhenov Formation reservoirs mainly relates to seismically-defined regional faults or to transverse faults.