Page 339 - Practical Well Planning and Drilling Manual

Section 3 revised 11/00/bc 1/17/01 12:00 PM Page 315

3.1.2
Well Control [ ]

the amount of overbalance is reducing (pore pressure gradient increas-
ing with depth). These warning signs indicate an impending problem
and preventative measures should be taken, such as increasing the mud
density to restore the overbalance. Indicators that may warn of decreas-
ing overbalance include:

Increasing rate of penetration in homogenous formations
Decreasing D exponent in homogenous, compressible shale forma-
tions
Increasing background gas level
Connection gas and/or trip gas
Increase in mud chlorides, if the source cannot be accounted for
from surface sources
Appearance of tensile failure mode shale cavings
If LWD tools are used, trends in resistivity or sonic velocities may
warn of pore pressure gradient changes

These trends need to be continuously monitored by the drillers and
mud loggers. Any changes should be cause for heightened monitoring.
Refer also to the topics on predicting pore pressures in Section 1.4.4,
“Pore Pressures and Fracture Gradients.”

3.1.2. Kick Detection and Response

Once flow from the formation has actually started, it must be
detected and action taken right away. The time between the flow start-
ing and the well being shut in will determine how much influx is
taken. Detection and response depends on maintaining the kick detec-
tion systems and continuous training of the drill crews.
Detection systems. These vary from low to high tech. It is easy to
get carried away with the high tech stuff, but do not forget the value of
the simpler systems.
When I was a trainee driller in Holland, the driller used to send me
and a fellow trainee down to the mud pits while we drilled. It was winter
and very cold; we had to hug the desilter feed pipes to keep warm. Every
so often someone would come along and adjust the nut hanging on a rope
attached to the handrail so that the nut just kissed the surface of the mud

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