Page 463 - Practical Well Planning and Drilling Manual

Appendix NEW! revised 11/00/bc 1/30/01 3:29 PM Page 439

Appendix 1
Calculating Kick Tolerances [ ]

Several safety factors support this:

Temperature will drop as the gas expands, reducing the pressure
peak at the shoe
The gas will disperse in the mud, reducing the pressure peak at the
shoe
If surface to bit volume is less than bit to shoe volume, kill mud
may exit the bit before the gas reaches the shoe, reducing the peak
pressure at the shoe

If the shoe strength is too low for the required kick tolerance, the
next casing shoe may have to be higher. If the mud gradient is changed,
recalculate the kick tolerance.
The heavier the mud weight used for drilling, the less tolerant the
well is (i.e., the shorter distance that can be drilled). A higher mud
weight gives less difference to the shoe strength; if mud weight equals
shoe strength gradient then MAASP = 0. Therefore, it follows that the
mud density should not be higher than is necessary for a trip margin
or wellbore stability considerations.
The rig should hold sufficient stock of barite to weigh up the com-
plete active system volume to the equivalent mud density achieved by
the FIT.
Kick tolerance volume. What determines the acceptable kicking
pressure and volume of kick tolerance?

1) The degree of risk. Higher assumed pore pressures should be used
for:
a) Wildcat exploration wells
b) Areas where short transition zones are expected
2) The speed of reaction. Higher volumes should be used when:
a) There are larger diameter holes
b) High permeabilities are expected from kicking formations
c) Drilling from a floating rig where flow detection may be tricky
due to heave
d) Low standard kick detection equipment is being used
e) Drill crews are not well trained (some third world countries
with local crews)

439