Severe mud losses hindered drilling operations and production potential

The Yurubcheno-Tokhomskoye oil field is a remote onshore project located in eastern Siberia. Most of the field's oil and gas reserves are found within highly fractured carbonate reservoirs characterized by extreme heterogeneity. The formation contains cavities ranging from microscopic fissures to large, cavernous thief zones that enlarge under high mud column pressure, leading to severe drilling fluid losses, total loss of circulation, kicks, and well control issues.

To continue drilling in these conditions, the operator applied lost circulation material (LCM), specialized pills, and cement bridges. However, in addition to reducing production rates, these interventions dramatically increased well construction time and total well cost. In some wells, the operator was unable to reach planned TD.

Multiphase MPD provided precise downhole pressure control

M-I SWACO, a Schlumberger company, recommended an integrated MPD solution that would mitigate severe fluid losses and reduce the need for lost circulation treatments. An RCD 3 rotating control device system provided a seal between the wellbore and the surface while enabling the pipe to move, rotate, and divert flow as needed. To help control bottomhole pressure, a LOW-PRESSURE AUTOCHOKE precision drilling choke console continually monitored for influxes, enabling surface backpressure in response to dynamic downhole conditions. M-I SWACO incorporated the SUPER MUD/GAS SEPARATOR high-capacity unit to maximize mud/gas separation, which improved circulation rates and safety during underbalanced drilling operations. The CARBONTRACKER gas flow measurement system measured the amount of gas flow coming from the well so the drilling team could determine equivalent circulating density (ECD) and gain a better understanding of well behavior. In addition, M-I SWACO decided to use drilling fluid with a specific gravity of 0.83 instead of 0.97, and a mobile membrane-type nitrogen unit for maximum flexibility and control over ECD.

Operator drilled multilateral well to TD with minimal losses and zero NPT

The operator successfully drilled all six planned laterals to TD with no NPT. The combination of nitrogen injection and new procedures for drilling and pulling out of hole reduced mud losses from 9,354 m³ to just 1,619 m³ [330,333.7 ft³ to 57,174.5 ft³]—a decrease of 83%.

The MPD solution also eliminated the need for potentially damaging lost circulation treatments,maintaining the formation's permeability and delivering a production rate 60% higher than predicted. All of these efficiencies helped reduce well construction time by 30% compared with conventional multilateral wells.