Page 340 - Practical Well Planning and Drilling Manual

Section 3 revised 11/00/bc 1/17/01 12:00 PM Page 316

[ ] Practical Wellsite Operations
3.1.2

in the tank. We did not know why this was done—no one explained these
things to mere trainees—and every so often if he did not appear, we
would do it for him. Of course what he was doing was monitoring the
level of mud in the active tank; an increase could be accurately seen as
long as the flow rate was constant (and no one messed with the nut).
Tank level monitoring systems using sound waves feed into the
driller’s totalizer system and also to the mud loggers computers. Alarms
can be preset at loss/gain levels to assist monitoring. These systems are
generally accurate and reliable. One in each corner with the signals
averaged may be needed on a floating rig to account for rig (and hence
mud surface) movement.
Floats that ride on pipes mounted in the tank also can feed com-
puterized detection systems. Float systems can stick on the pipe or
may leak; these are therefore less reliable than sonic (or nut on a
string!) systems.
A flo-sho is installed in the return flowline coming up from the
riser and bell nipple. When circulating, the return flow hits a paddle
that is pushed up. The position of the paddle is related to the flow rate
and mud density. If the well kicks, the first primary indication is an
increase in return flow rate in the flow line and a change in the posi-
tion of the flo-sho paddle, which will show on the driller’s panel. The
paddle can stick due to gumbo shale or other solids in the flow line,
which is often seen as an indicated flow even when flow has stopped.
Therefore, the flo-sho can give false indications of flow or may not
show a change even if the flow out changes.
All of these ways of monitoring the mud level suffer from one
major drawback; they only work when the system dynamics are not
changing. The flow rates have to be constant (could be zero) and have
to be stable (must have been constant for some time). If the pumps are
sped up, first the active tank level drops and then the flow at the flow-
line increases some time later. This increased flow feeds into the shak-
er tanks and sand trap, eventually reaching the active tank. It can take
several minutes on a deeper well for the flow into the active tank to
equal the flow out of it. A good driller will have a feel for how much is
gained by the system when the pumps are stopped for a connection
(could be over 20 bbls) and will monitor the totalizers to ensure that
the loss/gain indicator comes back to zero after a connection.
Computerized data acquisition systems have been developed for
slimhole drilling where very small influxes of around a barrel can be

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