Page 251 - Well Control for Completions and Interventions

Well Kill, Kick Detection, and Well Shut-In 245

7.3.3 Slow circulation rate
Most circulating kills are carried out at a slow circulating rate. To enable slow
circulation rate to be used effectively, slow circulation rate pressure (SCRP)
must be recorded at different pump rates with the pipe on the bottom.
SCPR is a record of pump pressure at any rate less than the normal circulat-
ing rate used to carry out work on the well and when the well is open.
During drilling operations, SCRP is taken regularly, normally at least once
per shift. However, for completion and workover operations, obtaining
SCRP rarely becomes routine since the pipe is not normally on the bottom
for any appreciable time. During most completions and workovers, the only
operations requiring pipe to remain on the bottom are the pre-completion
well bore cleaning trip, and remedial operations carried out as part of a
workover. Examples include performing a cement squeeze, milling a packer,
and cleaning fill from the bottom of the well. SCRP should be recorded any
time there is a change to the geometry of the workstring (internal or exter-
nal), or any time there is a change in the circulated fluid (density or viscosity).
Normal practice is to record SCRP at several circulating rates (Table 7.1).
If a well control incident occurs and the well needs to be shut-in, the
recorded SCRP is available to use when calculating circulating pressure
for the removal of a kick.
There are several reasons why a slow circulation rate is preferred:
• ECD on exposed formation. The higher the circulation rate the high-
er the ECD.
• Disposal of kick fluids. When circulating out a large kick, disposing of a
large volume of liquid hydrocarbon and contaminated brine will be prob-
lematic, especially on rigs with limited facilities. Slowing the pump rate
allows the crew to deal with returning hydrocarbons in a controlled manner.
• Reaction time on the choke. A circulation kill relies on maintaining a
constant BHP. Control of surface pressure (and by extension BHP)
can be difficult as the kick approaches surface—especially with a gas
kick. A slow circulation rate gives the choke operator more time to
respond to changing surface pressure.

Table 7.1 Example of recorded slow circulation rate pressure
Strokes per minute (bbls/st 5 0.0313) bbls/min psi
20 0.626 420
30 0.939 605
40 1.25 1050
50 1.56 1840