Page 229 - Well Control for Completions and Interventions

Well Barriers 223

6.6 BARRIER REQUIREMENTS IN SUBHYDROSTATIC
RESERVOIRS
Where a reservoir is known to be subhydrostatic and incapable of
flow, then some operating companies and jurisdictions will allow work to
be carried out against a single well control barrier. Note that subhydro-
static wells are very often capable of flowing gas to surface.

6.7 WELL INTERVENTION WELL CONTROL BARRIERS

Many well intervention operations are performed on live wells.
The barriers are provided by pressure control equipment rigged up on
the Christmas tree. Pressure control equipment specifically intended
for use on live well interventions is described in some detail in the
chapters of this book dealing with wireline, coiled tubing, and hydrau-
lic workover (snubbing). The main barrier categories are summarized
here.

6.7.1 Wireline
Primary (first) barrier.
• Stuffing box or grease head and lubricator system.
• When the wireline toolstring is at the surface, the tree valves are
closed to allow the lubricator to be vented and opened. The
Christmas tree valves form the primary barrier.
Secondary barrier.
• Wireline BOP that can close around and seal on the wire in the hole.
For braided cable and e-line a dual ram BOP is required.
• Christmas tree valves if the wire parts and are ejected from the stuffing
box (grease head). If the wire is ejected from the stuffing box, pressure
should be contained in the lubricator by the BOP gland or ball check
in the stuffing box/grease head.
During fishing operations, there may be occasions where wire is
stripped through a closed BOP. In these circumstances, the BOP becomes
the primary barrier.
Tertiary barrier.
• Wire cutting shear seal BOP.
• Wire cutting tree valve.