Page 343 - Practical Well Planning and Drilling Manual

Section 3 revised 11/00/bc 1/17/01 12:00 PM Page 319

3.1.3
Well Control [ ]

False kicks; the ballooning effect (Formation overpressures due to
ECD). A permeable formation may become locally pressured up around
the wellbore by the extra pressure exerted when circulating. When
pumping stops, the formation returns mud to the annulus. This is
known as the “ballooning effect.” If this is not recognized and the well
is killed, it will be found that it flows again after circulation ceases.
This happens when a tight permeable zone takes slow losses while
circulating with a high ECD. The flow will take some time to develop
and may be hard to recognize at first because nothing may happen for
15 or 20 minutes. Stopping pumping for connections may not cause a
flow, so the formation becomes locally charged as high as the ECD while
drilling and then comes in during tripping. In deeper, smaller holes the
closed-in surface pressure may reach several hundred PSI. Warning sig-
nals may include:

Slow losses while drilling
Cuttings or LWD logs show sandstones of low permeability
Flow takes a long time to develop
Pressure buildup takes a long time when the well has been closed in
There is little difference between pressure on the drill pipe (Pdp)
and pressure on the annulus (Pan), unless the returning mud
brings with it some formation gas
There is a reduction in Pdp and Pan after opening the well and
allowing some mud out. For example, release a measured amount
through the choke (5 bbls), let pressure stabilize, and repeat until
a definite trend either way is seen. Increasing annulus pressure
indicates a kick.

Once the condition is confirmed, the well can be depressured in
controlled stages, monitoring pressures, and volumes. Do not increase
mud density; this will make the problem worse.

3.1.3. Drilling Below Normal Kick Tolerance Levels

Refer to Appendix 1 for calculating kick tolerances. The level of
kick tolerance required for drilling a hole section depends on several
factors:

319