BAKER HUGHES - Drilling Fluids Reference Manual

PRESSURE PREDICTION AND CONTROL
• Preventive training. It is absolutely essential that personnel be thoroughly trained in prevention
and containment of kicks. After a well kicks, it is too late to learn how to execute an engineered
approach to kick control.
Kick Recognition
Early detection is necessary for successful control of a well kick. The severity of the kick
depends not only on the differential between drilling fluid hydrostatic and formation pressures,
but on the kick volume as well. Early detection and prompt well closure is usually the
responsibility of the rig crew.
To help the rig crew recognize kicks and execute proper control procedures, pit drills should be
conducted on a routine basis. Pit drills can be initiated by a company man or rig tool pusher
manually activating pit level or flow indicators, and observing the reaction time of the driller
and crew. Drills conducted while drilling should include raising the kelly and stopping the
pump to check for flow. The Blowout Preventers are normally not closed unless an actual flow
exists. Drills while tripping may include installing a safety valve in the drillstring if the pipe is
inside casing. If drills are conducted on a routine basis as part of company policy, the rig crew
becomes conditioned to execute proper control measures in a minimum amount of time.
Kicks While Drilling
A kick occurs while drilling when the pressures of the formation drilled exceed the total
pressures of the circulating fluid column (hydrostatic pressure plus annular pressure loss, i.e.,
P ECD < P f ). Some occurrences that may be associated with a kick are,
• drilling break
• increase in flow rate
• increase in pit volume
• circulating pressure drop
• well flowing with pumps off
• increase in chloride content of fluid at the flow line
• gas cut fluid or increasing gas concentration in the fluid.
Drilling break – This is one of the first indications of a kick. For hydrocarbons or water to
enter the wellbore, there must be a permeable section containing a pressure greater than that
exerted by the fluid column. In soft sandstones, this condition usually causes a sudden increase
in drilling rate. The magnitude of the increase varies, but an increase of 200% to 300% is not
unusual in soft sediments. Any significant drilling break should be checked for flow. This is
done by stopping the pump and checking the flowline to see that flow stops. If the well
continues to flow, it should be shut-in and checked for pressures.
In hard formations, a reverse break to a slower drilling rate may indicate a sand or limestone
section. In this case, the increase in drilling rate with flow into the wellbore is masked by
harder formations. However, a reverse break can also be the first indication of an overpressured
formation.
BAKER HUGHES DRILLING FLUIDS
REFERENCE MANUAL
REVISION 2006 12-17