Chapter 3: Wireline logging
Logging while drilling (LWD)
LOGGING WHILE CORING
What are logs?
“When someone mentions a log, he or she
is usually referring to records run on an
uncased wellbore using an electric wireline
logging truck and tools. Logs can also refer
to the driller’s log, mud logs, computer-
generated logs, and MWD (measurement
while drilling) logs.”
( D.E. Johnson and K.E. Pile
Well Logging in Non-technical Language, 2nd ed.
PennWell Publishing Co., Tulsa, USA, 2002 )
Some types of wireline logs can also
be run in wells after they have been
cased (e.g., gamma-ray; pulsed
neutron)… Schlumberger (1989)
• The wireline logging operation showing
logging truck (right), logging cable strung
into the rig, then lowered into the borehole
(left), with logging tools at the end of the
cable (bottom).
• Logs are usually recorded while being
pulled upward by the winch in the logging
truck.
• Most logs can also be run as an integral
part of the drill string (logging while
drilling or LWD) or attached to coiled
tubing. These methods are useful in
deviated, horizontal, or other hostile well
environments.
Cased holes vs Open holes
Examples of four logging tools.
•The dipmeter, on the left, has
sensors on four actuated arms,
which are shown in their fully
extended position. Attached to the
bottom of one of its four arms is an
additional electrode array
embedded in a rubber ‘pad’.
• It is followed by a sonic logging
tool, characterized by a slotted
housing, and then
•a density device with its
hydraulically activated back-up arm
fully extended.
•The tool on the extreme right is
another version of a dipmeter with
multiple electrodes on each pad.
Courtesy of Schlumberger.
SOME QUESTIONS ADDRESSED BY
LOG INTERPRETATION
• Geophysicist / • Reservoir Engineer
Geologist – How thick is the pay zone?
– How homogeneous is the
– Are potential zones zone?
porous? – Porosity?
– Formation intervals? – Permeability?
– Lithology?
• Production Engineer
– Hydrocarbons? – Which zone(s) to
– What type of complete?
hydrocarbons? – What production rates?
– Any water production?
– Commercial
– Will well need stimulation?
quantities? – What stimulation would be
best?
Recoverable STO (Stock Tank Oil)
porosity Oil Saturation
Area
Recoverable STO = A x h x x (1-Sw) x RF
FVF
Recovery factor
Height Formation Volume Factor
Saturations H2O (Sw) So = 1 – Sw
Oil
(So)
Oil
Common Types of Wireline Logs
•Resistivity/Conductivity: Fluid saturations.
•Sonic: Porosity, seismic correlation, mechanical
properties.
•Spontaneous Potential (SP): Lithology indicator (high vs
low permeability formations).
•Gamma-ray: Lithology indicator (high GR for clays).
•Photoelectric Factor (PE): Lithology indicator.
•Bulk Density: Porosity, gas detection.
•Neutron Porosity: Porosity, gas detection.
•Caliper Logs: Cement volume analysis; hole quality
indicator; borehole breakout analysis.
•Borehole Image Logs: Identify the presence,
characteristics and orientation of bedding or fracture
planes.
CHOOSING A LOGGING TOOL
It is necessary to choose the right tool to get the desired
measurement.
Considerations:
• Hole conditions ( depth, deviation, hole size,
mud type )
Examples:
– Oil based mud: Induction tool
– Water-based salty mud: Laterolog Tool
• Formation fluid content (fresh/salt connate
water)
• Economics (cost of the job, rig time involved)
DEFINITION
Resistivity logging is a method of well logging
that works by characterizing the rock or
sediment in a borehole by measuring its
electrical resistivity. Resistivity is a
fundamental material property which
represents how strongly a material opposes
the flow of electric current.
TYPES OF LOGS TO BE RUN
• Logging suites generally include one resistivity
and one porosity device
• The logging string will also have other tools like
the gamma ray, SP and caliper tools
• However, logging suites usually have two
porosity devices to give more information about
rock type, hydrocarbon type and porosity
• Other considerations – to estimate permeability
or to take fluid samples – require other special
tools like the formation testers
TYPES OF LOGS
• Permeable zone logs
- Spontaneous Potential (SP) Log
- The Gamma Ray (GR)Log
• Resistivity logs
• Porosity logs
The definitions of each symbol used in Figure 1 are listed as
follows:
dh – hole diameter
di – diameter of invaded zone (inner boundary flushed
zone)
dj – diameter of invaded zone (outer boundary; invaded
zone)
rj – radius of invaded zone (outer boundary)
hmc – thickness of mudcake
Rm – resistivity of the drilling mud
Rmc – resistivity of the mudcake
Rmf – resistivity of mud filtrate
Rs – resistivity of shale
Rt – resistivity of uninvaded zone
(true resistivity)
Rw – resistivity of formation water
Rxo – resistivity of flushed zone
Sw – water saturation of uninvaded zone
Sxo – water saturation flushed zone
