Page 386 - Practical Well Planning and Drilling Manual

Section 3 revised 11/00/bc 1/17/01 12:00 PM Page 362

[ ] Practical Wellsite Operations
3.3.2

It is possible (though not always necessary) to run logs to identify
which zone is responsible. A temperature log may identify the forma-
tion, or radioactive tracers can be pumped and a log run to detect the
radioactivity caused in the loss zone. The time and expense taken to do
this must be justified by the severity of the situation and the improve-
ment in decision making that should result.
In general, several techniques should be useful in most loss situations
deeper in the well in smaller holes. In order of attempting, these are:

1. Decrease circulation rate for lower ECD and drill with controlled
parameters to minimize annulus loading. The losses may well
decrease over a period of time (a few minutes to a few hours). The
severity of the loss may dictate whether this is acceptable, for
instance with losses of over 60 bbl/hr using expensive mud the
cost may be too high. Restricted replacement mud supply may
also preclude this.
2. Reduce mud density if possible by dilution and/or maximizing the
use of solids control equipment.
3. Pump a 100 bbl LCM pill around with around 45 ppb mixed
fine/medium/coarse LCM. Spot across and above the loss zone and
observe the well. When the well becomes static, break circulation
cautiously, monitor active volume, and resume drilling.
4. Add solids (LCM) to the mud to increase plastering characteristics.

Further action may include setting barite plugs, diesel oil bentonite
plugs or cement plugs, drilling with partial or total losses, setting an
extra casing string, or plugging back and sidetracking if the severity of
the losses warrants it.
Recommended procedure for curing total losses with cement.
You should adjust this procedure to the particular circumstances. The
general procedure is:

1. Drill ahead blind until it is anticipated that the loss zone has been
completely penetrated. Do not pump Zonelock pills, LCM, fibers,
or anything similar that might impede the movement of slurry into
the loss channels around the wellbore.
2. Run in with a smaller bit (say 8 1 /2 in in a 12 1 /4in hole) without noz-
zles on HWDP and drillpipe to about 10 m above the loss zone.

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