Drillpipe can be rotated and tool joints stripped through a
closed packer while maintaining a full seal on the drillpipe.
Longest packer life is obtained by adjusting the closing
chamber pressure just low enough to maintain a seal on the
drillpipe with a slight amount of drilling fluid leakage as the
tool joint passes through the packer. The leakage indicates
the lowest usable closing pressure for minimum packer wear
and provides lubrication for the drillpipe motion through the
packer.
A pressure regulator valve should be set to maintain the
proper closing pressure. For stripping purposes, the regulator
valve is usually too small and cannot respond fast
enough for effective control, so a surge bottle is connected
as closely as possible to the BOP closing port (particularly
for subsea installations). The surge bottle is pre-charged
with nitrogen, and is installed in the BOP closing line in order
to reduce the pressure surge which occurs each time a tool
joint enters the closed packer during stripping. A properly
installed surge bottle helps reduce packer wear when