Page 432 - Practical Well Planning and Drilling Manual

Section 3 revised 11/00/bc 1/17/01 12:00 PM Page 408

[ ] Practical Wellsite Operations
3.6.1

this will be similar to the one pulled or similar to the next bit planned
or an intermediate choice. The process that was used to make the bit
program can be repeated fairly quickly if the rig has all the following
information available: recommendations in the drilling program, hole
section summaries, offset bit data, field operational notes, and the end
of section reports from offset wells used during well planning. These
can be added to the drilling program as appendices and/or to the
drilling manual. The rig site PC can have a copy of the BITREX data-
base, or printouts/offset bit records from it can be appended to the
program. (See Section 2.4.2, “Comparing bit records using the
BITREX database.”)
Sometimes the next bit in may have to drill to a particular depth
(coring point, for instance), which is considerably less distance than
would be expected from a full bit run. It may be possible to run a
cheaper (or used, re-useable) bit instead. The rig needs a list of bit
prices and the drilling supervisor should consider bit cost when mak-
ing the selection. For example, it may be that the bit being pulled early
has already drilled through an abrasive zone where premium gauge
protection was used. The next bit in may not require this expensive fea-
ture and so a cheaper alternative may be possible.
If the preferred bit is not available. Occasionally the recom-
mended bit will not be on site. In this case, the drilling program
already defines the features required of the bit for a particular interval
and an alternative can be chosen from what is available by applying
those criteria. It is not recommended to merely substitute another bit
of the same IADC code because this code is a great simplification of
the bit features.
Where the onsite drilling supervisor runs a bit that is not in accor-
dance with the program recommendations, the choice must be justified
in the end of section report. This requirement will encourage careful con-
sideration before making a decision. The basis for this decision is also
important when evaluating the performance and planning the next well.
Refining bit choice and parameters based on previous bit run. A
good bit choice, run correctly and pulled at the end of its economic life,
should show worn cutting structure and/or bearings. Severe dull bit
features (excessive gauge loss, broken cutters, cones locked, etc.) are
warnings that something went wrong, especially if the performance fell
below expectations.

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