A re-entry drilling campaign of six highly deviated wells was successfully drilled from a fixed offshore platform through depleted reservoirs by utilizing managed pressure drilling in eight hole sections. The main challenge was the narrow drilling window of 0.05 to 0.60 ppg between wellbore stability mud weight, driven by unstable shales, and reduced fracture gradient of the reservoir sands, driven by depleted pore pressure. The necessity to balance risk of lost circulation, hole cleaning, and wellbore stability drove the team to employ new technology in order to achieve success.

Managed Pressure Drilling (MPD) is one of several technologies for optimizing drilling operations and reducing Non-Productive Time (NPT) while drilling narrow windows. The Surface Back Pressure (SBP) variant of MPD can be used not only on exploration wells with pore pressure uncertainties to identify and control influxes, but also can be employed in severely depleted reservoirs to enable drilling operations which are conventionally unattainable due to constricting drilling window.

This case study discusses the main objectives and requirements for MPD, along with the planning, equipment, and execution strategies used to drill and make connections with a mud weight statically underbalanced to wellbore stability gradient. Furthermore, the paper discusses the use of novel pressure testing techniques and automated fluid displacements with the MPD system to maintain a constant anchor point pressure prior to tripping and avoid losses and wellbore collapse. Finally, this study provides results, achievements, and recommendations on SBP application in a brownfield reservoir.

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