BAKER HUGHES - Drilling Fluids Reference Manual

PRESSURE PREDICTION AND CONTROL
• Watch annulus pressure, stop pump when annulus pressure starts to increase.
• Read drillpipe pressure at this point.
• If annulus pressure increased above original pressure, this would indicate trapped pump pressure
and the amount of increase must be subtracted from the shut-in drillpipe pressure.
This procedure should be repeated until the same value is read two consecutive times.
or
• If a predetermined circulating pressure has been measured at a circulation rate which will be used
to kill the well then,
• Open choke and start pump slowly, holding annulus pressure at same level as shut-in annulus
pressure.
• Bring pump speed up to predetermined kill rate, keeping annulus pressure constant.
• Read pump pressure; subtract predetermined circulating pressure from pumping pressure. The
remainder will be shut-in drillpipe pressure.
Fluid Weights and Pressures
Drillpipe pressure (or casing pressure) can be converted to Equivalent Fluid (Mud) Weight
(EMW) and vice versa. In the following discussion on fluid weight increase, the equation used
to convert pressure to fluid weight (lb m /gal) is,
Fluid Weight
Increase,
lb
m
/ gal
SIDP
= 0. 052×
( TVD)
Where:
SIDP = 260 psi,
TVD = 10,000 ft,
Fluid weight = 12. 0 lb m /gal.
260 psi
Fluid weight increases, lbm / gal =
= 0.5lbm
/ gal
0.052×
10,000 ft
This is th e fluid weight increase needed to balance formation pressure.
Therefore,
Initial fluid weight
Required weight increase
Total
12.0 lb m /gal
+ 0.5 lb m /gal
12.5 lb m /gal
When pressure is held on the circulating system with an adjustable choke, the additional
pressure is felt throughout the system, including at the bottom of the hole and at the drillpipe
pressure gauge. As fluid weight is increased to kill a kick, the pressure held by the choke is
replaced by hydrostatic pressure from the heavier fluid. Thus, the choke is adjusted as heavier
BAKER HUGHES DRILLING FLUIDS
REFERENCE MANUAL
REVISION 2006 12-23