BAKER HUGHES - Drilling Fluids Reference Manual

PRESSURE PREDICTION AND CONTROL
Figure 12 - 13 “U” Tube Shut In
A gain in pit volume equal to the volume of intruding fluid will then occur. When the well is
shut in, pressure on the drill pipe will be equal to the difference between formation pressure
and hydrostatic fluid pressure. Since hydrostatic pressure can be calculated from the known
height and weight of the fluid column inside the effect represents a pressure gauge by which
formation pressure can be determined.
Formation pressure = Hydrostatic pressure + SIDP
The following is a summary of the pressures in Figure 12-13.
Drillpipe Pressures
Formation pressure @ 10,000 ft - Hydrostatic Pressure @ 10 lb m /gal fluid = Drillpipe psi
5700 psi - 5200 psi = 500 psi
Annulus Pressures = Hydrostatic Pressure
1000 ft × 0.052 × 1.0 lb m /gal = 52 psi (1000 ft gas)
9000 ft × 0.052 × 10.0 lb m /gal = 4680 psi (9000 ft fluid)
Total Hydrostatic Pressure
52 psi + 4680 psi = 4732 psi (column)
Casing Pressure
5700 psi (Formation pr essure) - 4732 psi (Hydrostatic pressure) = 968 psi (Casing pressure)
When circulating out a kick at a reduced pump rate, it is necessary to hold pressure on the
drillpipe gauge in addition to the reduced circulating pressure. This is accomplished by
circulating through an adjustable choke. When beginning a kill operation, this additional
pressure equals the SIDP (see Figure 12-14).
BAKER HUGHES DRILLING FLUIDS
REFERENCE MANUAL
REVISION 2006 12-28