Page 139 - Well Control for Completions and Interventions

Completion Equipment 131

• Control line fluid and the fluid in pump used to pressurise the control
line must conform to a high standard of cleanliness. Some companies
e
use NAS (National Aerospace Standard) 6 or 8 specification :
• The valve must be function tested at the rotary table before it is run.
A record should be made of the fluid volume required to fully open
the valve, and the fluid volume returned from the control line when
the valve is closed.
• The control line should be run with pressure applied (valve open).
Loss of pressure will give an early indication of line damage. An open
valve also allows the well to be monitored.
• If the control line is damaged, the valve must be pulled back to the
surface, and the line replaced. It is not normally permissible to splice a
safety valve control line.
• The valve should be run as close as possible to the programme depth.
Do not run valves deeper than the programme depth, they may fail to
close.
• Monitor control line pressure at production start-up. Thermal expan-
sion of the fluid in the control line caused by increasing flowing tem-
perature can cause the hydraulic piston operating pressure to be
exceeded.

3.19.6 Annulus safety valves
Annulus safety valves (ASVs) were developed primarily for use in gas lift
wells. They are designed to retain high pressure hydrocarbon (lift) gas in
the annulus in the event of a loss of integrity at the wellhead. An annular
safety valve is basically a modified permanent releasable production
packer. The packer is equipped with a port that allows annulus fluids to
flow past the packer. Within the port is a fail-safe valve held open using
hydraulic pressure. Like the conventional safety valve, the pressure to
keep the ASV open is supplied from the surface through a control line.
Loss of hydraulic pressure causes the valve to close (Fig. 3.36).
ASVs are nearly always run just below the tubing safety valve. If they
were positioned above, the control line for the tubing safety valve would
have to be cut and fed through the ASV. Splicing the control line to feed
it through the ASV would have a detrimental effect on the reliability of
the tubing valve.
e
NAS Grade 1638 is a widely adopted standard to measure the contamination degree of
hydraulic oil.