This article was
especialy for "Crain's Petrophysical Handbook" by E. R. Crain,
P.Eng. in 2004.
Updated 2016, 2018.
webpage version is the copyrighted intellectual
property of the author.
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RECOMMENDED LOGGING PROGRAM
logging program should be carefully designed to gather all the data
required today, and in the future as well. The program needs to be
written, preferably in a checklist format, describing the logs to be
run, the curve complement on each log, the scales for each curve,
and the interval to be covered. The program forms part of the well
drilling and completion program and is used by the logging engineer
to guide hin as to what is required. The wellsite representative
(geologist, drilling engineer, or petrophysicist) monitors the
performance of the logging operation based on this program.
In the past, too few logs were run, even after the advent of many
of the modern logging and analysis techniques. Thus re-evaluation
of by-passed reserves, definition of geological prospects, and
seismic modeling suffer today for the false economy of the past.
The best procedure to follow is to run a comprehensive suite of
logs. Clearly there are economic constraints, such as in shallow
gas or coal bed methane projects, where a full suite of logs is not
helpful. You may be required to carefully tailor the log suite to
suit the circumstances. Here are my recommendations.
It has become common to just ask for a
or "quuad-conbo" and hope for the best, without thinking too much
about which specific log curves or tool types will appear in the
final delivery. For example, which of several resistivity or sonic
log varieties do you want for this job? Is shear sonic needed for
the seismic team? Are PEF and spectral GR included? Answers to these
questions are vital in unconventional reservoirs.
Here is what the generic terms mean
Triple-combo = resistivity + density + neutron
Quad-combo = resistivity + sonic + density +
The gamma ray log is always included but doesn’t add to the tool
A standard triple-combo is resistivity curves (with GR or SP or
both) plus density – neutron curves (with GR, caliper, density
correction, and PEF. Density + neutron counts as 2 of the 3 tools.
Array induction or high-res array laterlog are preferred for
quad combo adds a sonic log to the above tool string. This includes
only compressional sonic. You may want to add dipole shear sonic and
spectral ganna ray.
combos can have spectral GR, which adds potassium, thorium, and
RECOMMENDED LOGGING PROGRAM
normal (fresh) mud systems, use:
1. array induction SP, compressional-wave sonic, and
density neutron PEF GR Caliper (quad-combo)
SP, gamma-ray, caliper, borehole volume integration, and sonic integration curves
should be included on the induction and sonic log
presentations, and the
caliper, gamma-ray, density correction, cable tension,
and photo electric capture cross section (PE) should
be included on the density-neutron. The newest version
of each tool should be used, especially in overseas,
offshore, or frontier locations.
Many people eliminate the sonic log and run a triple-combo, but this
means you will never be able to accurately tie seismic data or
seismic inversions to this well.
density porosity and neutron porosity on sandstone scale in
sand-shale sequences, and limestone scale in carbonate sequences.
Use dolomite scale sparingly and only in pure dolomite sequences.
extras in fresh mud include:
2. dipole shear sonic if horizontal wells or frac
jobs are planned
for thin bed definition - can be run with density
log in certain
4. resistivity or acoustic image for stratigraphic
and structural data, and in fractured
or unconventional reservoirs
5. nuclear magnetic resonance log for shale free
connected porosity (especially in
unconventional shale gas
and shale oil plays)
6. elemental capture spectroscopy log for detailed
salt mud, or high resistivity formation with
fresh mud, replace or augment the induction with array
or high resolution laterolog.
reservoirs, add the dipole shear sonic log with crossed dipoles and
the resistivity image log to define fracture orientation and stress
regime. Post-processing for fracture aperture and fracture porosity
reservoirs, add the gamma ray spectral log to distinguish uranium,
potassium, and thorium.
In very shaly
sands, or in carbonates with micritic or highly varying pore
geometry, run a nuclear magnetic resonance log to determine
irreducible water saturation.