The Yurubcheno-Tokhomskoye oil-gas-condensate field is located in the north of the Krasnoyarsk region and is one of the largest fields in Eastern Siberia. The deposit was discovered in the 1980s, but its development began only in 2009. The operator of the field is East Siberian Oil and Gas Company JSC, which is part of the structure of Rosneft Oil Company.
The oil and gas potential of the Yurubcheno-Tokhomskoye deposit is associated with carbonate and terrigenous deposits of the Vendian and Riphean. The practice of drilling in a fractured reservoir of Riphean deposits using traditional solutions is associated with catastrophic lost circulation of drilling mud reaching several thousand cubic meters. A large volume of losses leads to decrease in the drill-in quality of productive layers, an increase in the construction time and the cost of wells. The use of lost circulation materials (LCM) has shown relative effectiveness due to a wide range of fractures sizes and the difficulty of selecting the optimum LCM composition for such conditions.
In 2016, a set of solutions was implemented in the framework of pilot projects to reduce the intensity of mud losses by controlling the bottomhole pressure (equivalent circulating density (ECD)) while drilling with the use of dynamic pressure management technology (DPM) and nitrogen injection. To achieve the minimum ECD, along with the DPM, it was required to optimize the remaining components of the drilling process, including directional drilling, drilling measurements, bits and drilling fluids. The implementation of this set of solutions has significantly reduced losses of drilling mud (at the first well, the volume of lost drilling fluid was about 500 m3, which is much less the average volume of 2100 m3 in the wells drilled in 2015-2016), to shorten the drilling time for the productive interval and increase initial productivity of wells. During the pilot project, 4 wells were drilled with a consequent optimization of the solutions as experience gained. The results of the experimental work were recognized as successful and a decision was made to replicate the technology for drilling the fractured reservoirs of the Yurubcheno-Tokhomskoye deposit.
