Page 306 - Practical Well Planning and Drilling Manual

Section 2 revised 11/00/bc 1/17/01 12:04 PM Page 282

[ ] Well Programming
2.8.1

It is very important that the proposed logging program is reviewed
by the drilling department and modified as necessary to provide the
most accurate information for future well planning. The following brief
summary shows what kind of information is needed and how it helps
improve future plans. Note that for convenience the abbreviations are
for Schlumberger wireline tools. Other logging contractors will provide
equivalents for some or all of these.
Wellbore profile from a 4-arm caliper. Immediate use is to calculate
cement volumes and to spot thick filter cake buildup, which may flag
up potential differential sticking of drillstring or logs. Ledges and
washouts will show where special care needs to be taken for logging or
running casing. For later evaluation, the shape of the hole and the mea-
surements of minimum and maximum sizes give information on how
directional the field stresses are. Enlarged sections are worthy of defin-
ition and study so that the enlargement mechanisms can be identified
and possibly mitigated on the next well. (Refer to Section 2.9.1.)
Sonic data. Sonic properties for shear and compressional waves can
be evaluated to give rock mechanical properties and information on for-
mation stresses. Stoneley waves from the dipole shear sonic indicator
(DSI) can also be evaluated to give permeabilities. This will aid in bit
selection, wellbore stability studies, fracture gradient, and pore pressure
prediction. Further, it may indicate fractured formations. It is important
to specify that the full waveform is recorded for rock mechanical prop-
erty evaluation; sometimes the loggers do not record the full waveform.
Long spaced sonic (LSS) is not sufficient, array sonic (AS) is better but
at a slightly higher cost, and dipole shear (DSI) is the best. If the explo-
ration program is for the LSS or AS, upgrade to DSI.
Sonic tools include the ultrasonic imager tool (USIT). It gives a
detailed picture of cement in the annulus (including microannulus and
channeling). The USIT also evaluates casing thickness and therefore
wear or other damage.
Temperature log. Determines geothermal gradients for cement,
mud, and brine design; also detects lost circulation zones.
Resistivity, porosity, and density data. Gives indications of potential
overpressure buildup. (Refer to Section 1.4.4.) May be useful for cor-
relation if LWD required in future wells.
Microresistivity. Detects fractures and faults (wellbore stability and

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