Page 257 - Well Control for Completions and Interventions

Well Kill, Kick Detection, and Well Shut-In 251

When the kill starts, tubing pressure will reduce quickly as the annulus
(packer) fluid fills the tubing. There are a few points to note:
• When the kill fluid has the same weight as the fluid already in the
annulus, pump pressure should be kept constant until the end of
the kill.
• If the kill fluid is heavier than the fluid in the annulus, pump pressure
will need to be stepped down to prevent over-pressure on the forma-
tion and potential losses.
• If the fluid needed to kill the well is lighter than the fluid already in the
annulus, then pump pressure will have to be stepped up to overcome
U tube pressure as the heavy annulus fluid fills the tubing. It will then
be stepped back down as the lighter kill fluid begins to fill the tubing.
With a known reservoir pressure and required overbalance, creating a
pump schedule is relatively simple. The surface pressure needed at the
pump for any stage of the operation is:

ðreservoir pressure 1 overbalanceÞ
annulus hydrostatic to the plug ðor reservoirÞ:

Tubing head pressure should equal:

ðreservoir pressure 1 overbalanceÞ
tubing hydrostatic to the plug ðor reservoirÞ:
Casing pressure is predictable and can be plotted against volume
pumped (or strokes). If the tubing contents are known, and GOC depth
is known, a prediction of tubing pressure can be produced and used to
assist the person operating the choke.
In vertical wells with single diameter tubing and single diameter
casing, the critical points during the kill are:
• Gas cap (if present) has been removed and liquid reaches the
surface.
• Oil/Water contact (if applicable) at surface.
• Annulus (packer) fluid fills the tubing.
• Kill fluid at the circulation ports.
• Full circulation is complete, at which point the well should be dead.
In deviated well and well with tapers in the tubing and/or casing, the
pump schedule will be more complex. Three examples of reverse circula-
tion well kills are demonstrated next.