Page 341 - Practical Well Planning and Drilling Manual

Section 3 revised 11/00/bc 1/17/01 12:00 PM Page 317

3.1.2
Well Control [ ]

detected. These monitor different parameters such as pump rates, flow-
line levels, and tank levels over time so that at any stage, even when
changing the pump rate, the computer can compare actual with pre-
dicted levels and flows.
The Mk 1 Eyeball should also be used whenever the driller has
any reason to think that the well might be kicking. If a secondary
indication such as a drilling break (sudden increase in penetration
rate) or a primary indication (increase in flow) is seen, a flowcheck
should be done.
Flowchecks are often difficult. With the pumps off, colder mud
that has just arrived downhole from the surface system will warm up
downhole and a small flow may result. On a floating rig, heave can
make it very tricky to decide whether or not the well is flowing. The
flowcheck must be kept going for long enough to be sure. A tight for-
mation may kick with a very slow influx rate. Further, the ballooning
effect (described below) can give a realistic “false kick,” which can
develop fairly high surface pressures if shut in.
MWD tools now play a significant role in kick prevention. Sperry
Sun offers a pressure detection service; a dedicated pressure engineer
stays in the logging cabin and monitors resistivity from the MWD tool.
A decrease in the resistivity trend with depth may indicate increasing
pore pressure gradients. The engineer will also monitor the levels of
gas dissolved in the mud, pressure cavings, D exponent, and other indi-
cators to buildup a picture of the pore pressure trends. If any increase
in pore pressure is indicated, it can be reported to the driller and
drilling supervisor for action to be taken.
Anadrill has an MWD tool that measures resistivity right at the bit
(RAB tool). The tool measures five resistivity values: at the bit, using a ring
electrode (for compensating certain formation effects), and at three button
electrodes (when configured as a stabilizer). The button electrodes mea-
sure formation resistivity Rt at depths of investigation of approximately 1
in, 3 in, and 5 in in an 8 /2 in hole size. Gamma ray, axial, and transverse
1
shock load measurements are also available from the tool.
Resistivity at the bit is obtained by inducing a voltage above the bit and
measuring the axial current flowing through the bit and into the formation.
Response training and drills. All the best detection equipment is
useless if the driller does not respond when a kick is indicated. Regular
drills should be initiated to train the drill crew and test their response.
The two most common drills are a pit drill and a trip drill.

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