Drilling in deepwater presents a significant challenge. With an increase in drilling operations in harsh environments, drilling riser requirements and limits have become more onerous due to uncertainties involved in response prediction and prolonged drilling programs. The following are the main objectives of this paper:
• Emphasize the criticality of conducting analysis of drilling risers in deepwater environments;
• Highlight drilling riser monitoring as a key integrity management tool;
• Discuss briefly the strides in development of alternatives to conventional deepwater drilling riser systems.
The factors that affect deepwater drilling riser integrity are as follows:
• Increased wall thickness for hoop load resistance from mud head and collapse resistance from water column;
• Higher top tensions, requiring increased wall thickness and vessel capability;
• Larger curvature resulting in potential wear issues from drill string rotation;
• VIV due to severe currents generating high fatigue damage in short periods of time;
• Conductor fatigue damage due to lower BOP stack vibrations at certain current speeds;
• Longer joint requirements – handling issues during riser deployment and retrieval;
• Increased importance of auxiliary line designs due to load sharing between main riser pipe and auxiliary lines.
Deepwater drilling riser engineering is complex. A high level of understanding is required of the response of the system to various conditions, and the design issues that govern the system.
The paper is based on extensive work pertaining to deepwater drilling riser projects that have been carried out during the past decade in the Gulf of Mexico, North Sea, offshore Brazil and West Africa. The lessons learned from these projects can be applied to improve future design practices. In addition, this also leads to knowledge transfer to other areas of the world with emergent deepwater developments.
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