Page 247 - Well Control for Completions and Interventions

Well Kill, Kick Detection, and Well Shut-In 241

• Keeping the hydrocarbons contained in the tubing can be advan-
tageous if the tubing has a higher burst rating than the casing,
but can be a disadvantage of the tubing is badly worn or
corroded.
• In some pre-workover or intervention situations, the packer fluid will
be dense enough to overbalance reservoir pressure, thus simplifying
the kill.
• In some deep-water subsea wells, ECD will be lower when reversing,
a consequence of frictional pressure drop through the choke line (see
Chapter 14, Well Control During Completion and Workover
Operation).
Although the reverse kill is generally acknowledged to be beneficial,
there are some concerns.
• In most cases, reverse circulation ECD is higher than during conven-
tional forward circulation. Fluid being pumped to the surface through
thetubingmustovercomefriction. Sincetubingusually hasasmaller
cross-sectional area than the annulus, more frictional pressure drop
1
occurs when reversing. For example, 4/2 in.12.6 lb/ft.tubinghas a
capacity of 0.0152 bbls/ft. Placed inside 9/8 in. 47 lb/ft. casing the
5
annulus has a capacity 0.0535 bbls/ft., 3.5 times more than the
tubing.
• High ECD will result in more fluid loss to the formation unless
the well is plugged below the circulation ports or effective LCM is
used.
• High pump pressure in the annulus will result in increased collapse
loading on the production tubing. Tubing weakened by corrosion is at
risk of collapse.
• Debris that has settled above the production packer can block circula-
tion ports.
• If the well is plugged below the circulation ports, reverse circulation
will sweep debris from the annulus into the tubing. The debris will
settle above the plug, making post intervention recovery more compli-
cated and time consuming.
• In gas filled wells, small adjustments to the choke often result in large
changes in circulation pressure owing to gas compression and
expansion.
• Heavy fluid in the annulus. If reservoir pressure declined after
the well was completed, the fluid in the annulus (packer fluid)