Page 226 - Well Control for Completions and Interventions

220 Well Control for Completions and Interventions

• Surface controlled “inflow control valves.”
• Formation isolation valves (of the type commonly used during gravel
packing operations).
• Cemented liner or casing.

6.2.2 Fluid barriers
A static column of mud or brine of sufficient density to overbalance the
highest anticipated reservoir pressure can be classified as a fluid barrier.
Mud is classified as a barrier where:
• The mud can be conditioned (circulated) to keep the solids in suspen-
sion. If mud remains static for too long the mud solids (barite) will
begin to settle, and the mud will lose density.
Brine can only be classified as a barrier if certain conditions are met:
• Since brine contains no solids, losses are probable unless lost circula-
tion material (LCM) is held against the formation.
• Where LCM is required to prevent losses, the brine cannot be classi-
fied as an independent barrier, since it is dependent on the effective-
ness of the LCM to maintain a hydrostatic overbalance.
• In low permeability reservoirs, e.g., shale, no LCM is required, and
brine can be classified as an independent fluid barrier.
• Brine can only be classified as a barrier if the fluid level can be contin-
ually observed and the fluid level maintained.
• If a brine column is supported by a mechanical barrier, e.g., a plug, it
can only be considered a single barrier, since it is dependent on the
plug integrity.
• Where fluid losses are permissible, the loss rate must be less that the
agreed limit.

6.3 BARRIER TESTING

Until successfully tested, no mechanical or fluid device can be con-
sidered a well control barrier. The normal method for testing mechanical
barriers is to apply differential pressure. The main considerations are:
• Differential pressure: Test pressure (Δ p ) must be more than the antici-
pated maximum differential the barrier will be exposed to when in