Subsea Marine Riser Systems

A marine riser system provides a fluid conduit to and from the wellbore—that is, it extends the wellbore from the subsea BOP to the drilling rig. It also supports auxiliary lines, such as high-pressure choke and kill lines, mud booster lines, and hydraulic conduits.

Further,the marine riser system guides the drill stem and other tools from the drilling rig to the wellhead on the seabed.

Finally, it provides a means of running and retrieving the BOP assembly from the surface to the wellhead on the seafloor.

Marine riser systems are critical equipment; therefore, if a system fails, catastrophic losses can result. Consequently, the overall design of the system is of paramount importance. Generally, system design begins with an assessment of expected operating conditions and an engineering analysis to establish such factors as tensile loads, bending stresses, maximum operational water depth, buoyancy requirements, surface tension, and vessel response to motion.

Additional factors that affect riser system design include:

• dynamic and axial loads while running and retrieving the riser system and BOP assembly;
• lateral forces from currents and vessel offset;
• cyclic forces from wave and vessel motion;
• vortex induced vibrations (VIVs);
• axial loads created by the weight of the riser system itself, the weight of the drilling fluid inside the riser, and the additional weight of
• freestanding pipe within the riser;
• axial tension from the tensioning system at the surface;