A North Sea operator had abandoned one of the inner slots of an offshore normally unmanned platform (NUI) that contained a stuck conductor, with the conductor shoe positioned 108 m below seabed at 1° inclination. Attempts to recover the conductor at the time proved unsuccessful and the slot was abandoned. However, the remaining slots on the platform were drilled and completed. With limited space and reservoir targets still to be developed, the operator later decided to use the abandoned slot to drill a production well. Given the stuck conductor and crowded platform, there were concerns for the integrity and safety of the surrounding wells.
Drilling of production wells must not only allow the reservoir to be developed, but also protect the integrity of the existing wells, and proceed in a safe manner. This requires compliance with company and governmental procedures, regulations, and best practices. To help ensure safe utilization of a compromised offshore slot (i.e., with a stuck conductor) on a congested platform, drilling had to comply with the company's strict anticollision (AC) policy of isolating health, safety, and environmental (HSE) risk wells. Extensive preventive measures were executed, including shutting in high-risk wells, evaluating current and offset wellbore conditions, and selecting the most appropriate drilling tools.
A custom drill bit was designed to provide the bottomhole assembly (BHA) control necessary to help minimize damage to the outside casing of any accidentally contacted well. This would further help mitigate the potential for drilling through multiple well barriers, and prevent expensive and complex remedial work. Field testing was critical to the design modifications and validated feasibility before use in the abandoned slot. These tests evaluated the new drill-bit design versus a conventional drill bit in a comparable, controlled environment.