Page 243 - Well Control for Completions and Interventions

Well Kill, Kick Detection, and Well Shut-In 237

• A gas influx migrates towards the surface more quickly in completion
brine than in mud.
• Many completion components, for example packers, are close to
casing ID. Restricted fluid by-pass around these components increases
the risk of swabbing and surging.
• Well integrity during workover operations is often compromised by
corroded and damaged equipment; consequently, controlling the well
becomes more difficult.
• Neither the annular preventer or pipe ram will seal around some types
of completion equipment, for example sand control screens and slotted
liners, nor will they seal around hydraulic control lines (flat pack),
instrument cables, and Electric Submersible Pump (ESP) cables.
• During many workover operations, the well is killed with the
Christmas tree still in place. If reverse circulation is used, hydrocarbons
from the well can be routed through the flowline to the process facili-
ties. This enables the well kill to be carried out in a closed, tested
system; a very low risk operation.

7.2 WORKOVER AND INTERVENTION WELL KILL
PLANNING

Killing the well is a necessary part of many workover and interven-
tion operations, and deciding how the well should be killed is a crucial
step in the planning process. Any well kill decision must consider the
type and condition of the completion, reservoir parameters, and the type
of surface equipment available.
Initially, the choice will be between a circulating or non-circulating kill,
with a circulating kill usually preferred since it is normally performed at
lower pressure and is generally much less likely to damage the formation. If
the Christmas tree is still in place, reverse circulation allows the tubing con-
tents to be displaced through the process facilities, a very safe and
environmentally-friendly way of removing the hydrocarbons from the tub-
ing. If the blowout preventer (BOP) stack has been installed, reverse circula-
tion is still normally preferred, as the hydrocarbons are kept in the tubing.
Where it is not possible to establish a circulation path, a non-circulating kill
method must be used; the two methods commonly used are:
• Bullhead
• Lubricate-and-bleed