Page 185 - Well Control for Completions and Interventions

Well Control Surface Equipment 177

liner. The well should be secured by using the kill-stand, or by cutting
the pipe and closing the blind rams.
• Installing and closing a FOSV in response to a kick results in an
upwards piston force equal to well pressure times the cross-sectional
area of the pipe OD. If there is not much tubing in the well, piston
forces will force the pipe up through which ever preventer has been
closed. Tubing couplings do not usually have enough taper to prevent
them damaging the annular preventer if they are forced through the
closed seal. Closing the pipe ram preventer may be enough to hold
the tubing, but not if it is weakened by corrosion. The safest option is
to use the kill-stand, the couplings on drill pipe having enough upset
to be retained by closed pipe rams.
It is good practice to stab a FOSV any time the tubing needs to be left in
the slips, for example whilst carrying out repairs or during a shift change.

4.10.4 Inside blow out preventer (gray valve)
An inside BOP, sometimes called a gray valve, is a non-return valve that
is used when drill pipe or tubing needs to be stripped into the well. It
prevents upwards flow, but allows fluid to be pumped down the pipe.
The most commonly used internal BOP features a rod that is used to
hold the valve off-seat until it has been made up to the tubing. With the
valve in place, the rod is released, allowing the valve to seat and shutting
off flow. The upper sub can then be removed and pipe can be made up
above the internal BOP and stripped into the well (Fig. 4.28).

4.10.5 Drill-string float valve
Non-return valves prevent an influx into the drill string during a kick.
They also prevent backflow of annular cuttings plugging bit nozzles.
Non-return valves are required by some drilling contractors and operating
companies when drilling and opening the hole before setting the surface
casing, or at any time the well control plan is to divert. They are often
used for drilling deeper sections of the hole.
There are two types of valve in widespread use, the flapper and the
spring-loaded dart (or ball).
These types of valves are not normally used during completion or
workover operations, since they prevent the tubing from filling as it is
run. When completion tubing is run with a valve in place, the tubing
needs to be filled from the top. The tubing displacement volume is much