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Drilling Riser
The marine (or drilling) riser is the communications link
between the drilling vessel and the subsea wellhead through which
downhole equipment is guided and mud is returned to the surface.
It also serves as a running string for the BOP stack. Improvements
in materials and construction have greatly reduced the probability
of riser failure, but proper care and use is still required to reduce
riser deterioration.
Without vessel motion, the marine riser would be just a line
of pipe like those used in land operations. Because of these
motions, however, the marine riser becomes a more complicated
system, requiring additional special equipment. In more complex
and hostile offshore environments, drilling risers must be designed
to withstand the maximum combinations of riser tension, internal
pressure, and bending moments without overstress or fatigue. The
physical demands imposed by drilling vessel excursions; wind,
current, and wave forces; and thermal expansion require extremely
reliable components.
A typical riser system is composed of a lower marine riser
package, riser joints with high-strength connectors, a telescopic
joint with terminal fittings and a tensioning ring, and a diverter. Of
course, a tensioning system must be incorporated and, in some
cases, buoyancy modules. Some risers also include a fillup valve
that prevents riser collapse in the event of drilling-fluid pressure
loss. Sometimes, in deep-water drilling, an upper ball (or flex)
joint is used with the telescopic joint. However, the necessity of
the additional ball joint is now being questioned since wells have
been drilled in over 2,000 ft of water without an upper ball joint.
The choke-and-kill lines may be attached integrally to the riser.
The lower marine riser package is a preassembled unit that
connects the marine riser to the BOP stack. Usually it is composed
of a lower marine riser guide frame enclosing a hydraulic
connector, an annular preventer, a flex joint, and choke-and-kill
flex lines. If a double female hydraulic control system is being
used, the guide frame also houses the intermediate female
receptacles, which in turn carry the control pods.
The flex joint in the lower marine riser package
accommodates up to 10° deflection from the vertical to allow for
any horizontal movement to which the drilling vessel might be
subjected. When using a ball joint, the weight of the riser and the

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