Case Studies Underbalanced Drilling
Foam Drilling in a Fractured Carbonate
Drilling Scenario
The Jean Marie formation is a fractured carbonate known for producing gas over a large area in the Northeast British Columbia, Canada. Most of the reserves are stored in a widespread fracture system, with additional contributions from the primary matrix porosity.
The use of underbalanced drilling technology has proven to be a competitive advantage by providing an undamaged reservoir and optimizing the recovery of reserves in the Jean Marie formation. As a standard practice, exploration wells were drilled underbalanced in order to minimize formation damage, determine the presence of gas-filled fractures, and provide real-time reservoir evaluation while drilling.
This particular case describes the underbalanced drilling operation experienced in a well drilled in a new area of exploration.
Technical Challenges
The major goals of this drilling operation were to drill a horizontal well while minimizing lost circulation and formation damage, yet maintaining optimal hole cleaning and drill cutting quality.
In order to achieve these goals through the horizontal interval, foam drilling was selected. The benefits of foam drilling include efficient hole cleaning at low liquid volume fractions. Due to the lower annular velocities, significantly lower compressor power was required compared to dry-air drilling technique. The use of foam was required to maintain underbalanced conditions in this reservoir, which had a pore pressure of 580 psi.
Project Results
At a measured depth of approximately 11,000 feet (~5,500 ft TVD), the horizontal exploration well was drilled using foam as the circulation fluid. The bottom hole pressure of the well was maintained at a pressure of 333 psi, thereby minimizing formation damage in the horizontal leg, which has a long exposure time to the drilling fluid, especially in the portion of the borehole closest to the bend. Through the use of foam, excellent cuttings quality was obtained, while providing effective hole cleaning in the horizontal leg. The quantity and size of cuttings were also greater than usually experienced when drilling other Jean Marie reservoir intervals.
