Case Study: Managed-Pressure Drilling Eliminates Circulation Loss and Achieves Zero NPT in Wilrich Formation

Operator makes @balance drilling services standard practice, implementing the technology for more than 20 wells in western Canada

Challenge: Avoid mud losses by managing equivalent circulating density (ECD) in a well with a narrow operating window between the pore pressure and fracture gradient.

Solution: Use @balance managed pressure and underbalanced drilling services to control ECD.


  • Significantly reduced mud loss and mitigated background connection gas, well kick, and stuck pipe issues.
  • Implemented @balance services for more than 20 wells, making it a standard operating practice for the field.

Avoid ECD issues in challenging well

Drilling the deep Wilrich Formation of western Canada often leads to significant NPT and multiple well abandonments due to high mud loss, background connection gas, well kicks, and stuck pipe issues. An operator in the area was drilling a 3,000-m lateral in this formation and found that the wide ECD range from heel to toe would open more of the pay zone. During conventional drilling operations, this ECD profile could exceed the fracture gradient or become underbalanced at the heel.

In this well, the pore pressure–fracture gradient window was 50 kg/m3 at the heel. The lateral pore pressure–fracture gradient window was 120 kg/m3. Because of these reservoir conditions, the operator sought a solution to manage gas flow, making it possible to drill within the narrow operating window and remain below fracture pressure to avoid losses.

Use managed pressure and underbalanced drilling services

M-I SWACO engineers recommended using @balance managed pressure and underbalanced drilling services for controlling ECD. These services help operators identify and prevent risks associated with unstable boreholes, uncertain pressure regimes, and narrow pressure windows.

For this operation, M-I SWACO determined the static mud weight below reservoir pressure, evaluated the trapping pressure on connection with a semiautomated choke, and used a mud-gas separator (MGS) to control and manage gas flow. The RCD 3 rotating control device was used to contain annular pressure and divert mud returns from the annulus through the rig degasser and separator. A Coriolis meter was also used for early indication of gas entrained in the fluid.

Constant evaluation was a significant factor in this operation. Multiple scenarios and schedules were engineered with VIRTUAL HYDRAULICS software to support bottomhole pressure management. The engineering team performed dynamic leakoff and flow checks to determine pore pressure and fracture gradient and to develop detailed plans and schedules. Hydraulics analysis helped determine a more progressive approach to resolving pressure control during tripping. In addition, an engineered displacement and tripping schedule was developed after excessive losses were observed during rollovers and during tripping operations. Surface pressure was applied at scheduled running speed during tripping operations to reduce kill mud-weight requirements by offsetting the bottomhole pressure effect from swab and surge.

Reduced mud losses, implemented across subsequent wells

Managed pressure drilling proved successful for drilling the Wilrich wells, providing significant reduction of losses. The operator has since chosen @balance services as standard practice, and more than 20 wells have been completed using this methodology to date.

Download: Managed-Pressure Drilling Eliminates Circulation Loss and Achieves Zero NPT in Wilrich Formation (0.10 MB PDF)

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