Experience from Drilling a Horizontal Well in a Naturally Fractured and Karstified Carbonate Reservoir in the Barents Sea Using a CML MPD System

Tangen, Geir Ivan (Lundin Norway AS) | Smaaskjaer, Geir (Lundin Norway AS) | Bergseth, Einar (Lundin Norway AS) | Clark, Andy (Lundin Norway AS) | Fossli, Børre (Enhanced Drilling AS) | Claudey, Eric (Enhanced Drilling AS) | Qiang, Zhizhuang (Enhanced Drilling AS)



In 2015, while coring in the carbonate reservoir in the second appraisal well on an oil and gas discovery in the Barents Sea (386 m water depth), the drill string fell 2 meters and a total mud loss was experienced leading to a well control incident. As a result, since 2016, the operator has introduced and used the Controlled Mud Level (CML) system. To date this system has been used on seven wells including two further appraisal wells on the same field and five exploration wells in the area.

In 2017 it was decided to drill a horizontal well in the same carbonate reservoir and to perform an extended production test in close proximity to the original loss well. Since it is not possible to predict where large voids (karsts) and natural fractures could be encountered, contingency to handle high losses, had to be implemented for the horizontal well. During the well planning, further risk reducing measures were implemented, including the use of wired drill pipe to improve the management of the wellbore pressure profile. This paper describes the planning processes leading up to the operation and the highlights of the operation itself together with the lessons learned. It elaborates on how wired pipe, used in combination with the CML system, added value to the operation. It shows how it was possible to drill the reservoir section with a low overbalance while managing severe losses associated with open karsts and natural fractures and still maintaining the fluid barrier. Despite the severe losses encountered it was possible to safely drill and complete the well without any well control event by use of the CML system.