Risermounted Chokekill And Auxiliary Lines
- 12.1 Function. These lines carry fluids along the length of the riser. On most risers, they are an integral part of each riser joint and are attached on the outside of the riser main tube by support brackets. Generally, these lines are used for the following:
- Choke/Kill lines are used to provide a controlled flow of oil, gas or drilling fluid from the wellbore to the surface when the blowout preventer stack is closed.
- Mud Boost lines are used as conduits for drilling fluid which is pumped into the riser just above the blowout preventer stack to increase annular circulating velocities.
- Air Inject lines are used to supply air to increase riser buoyancy for air can buoyancy risers.
- Hydraulic Supply lines carry hydraulic operating fluid to the blowout preventer subsea control system. Most blowout preventer systems incorporate a flexible hydraulic fluid supply line inside the control line hose umbilical.
- 12.2 Typical Designs. Typical riser joints have integral choke and kill lines. This provides redundancy and also allows for the following well control operations:
- Circulating down one line and up the other line.
- Circulating down the drill pipe and up one line.
A mud boost line is incorporated for some risers. Air inject lines are required for riser systems which use air-chamber buoyancy systems. Hydraulic supply lines can be used as either a primary or secondary supply line.
Generally, choke/kill and auxiliary lines of one riser joint are connected to their counterparts on adjoining riser joints by stab-in couplings. The box contains an elastomeric radial seal which expands against the smooth, abrasion-resistant sealing surface of the pin when the line is pressurized. These stab-in couplings also facilitate fast make-up while deploying the riser.
2.12.3 Selection Criteria. The following items should be considered when selecting, designing or specifying choke/kill and auxiliary lines for riser joints.
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