Introduction to Induction Logging

UNIVERSITYOF AZADJAMMUANDKASHMIR
MUZAFFARABAD
Induction logging
Prepared by :
Abdur Rauf (Group leader) 125
Naeem Arshad Samme; 153
Khunais Ahmad; 157
Ahsan Ali Naqvi; 113
Shayan Badshah; 115
Murtaza Khadim; 112
Presented To:
Dr. Ali Wahid
Assistant professor,
And whole class

What is Induction Logging
How it works?
Why do we use it?
3

Contents of Presentation
Log Presentation & Scale
Typical Log Response
Log Measurement Tools
Log Application
Background and formula used
Interpretation
4

Introduction
 A new logging method, called induction logging, is described; it
measures the conductivity, or resistivity, of the strata traversed by
a bore hole.
 The apparatus, which is briefly described, comprises a coil system
coupled with the ground by induction, so that there is no need for
direct contact with the mud, or with the formations.
 For that reason, the method is particularly useful in oil base mud, and
it was first applied to that case.

 A discussion concerning the respective contribution of each region
of grounding the vicinity of the coil system is given.
 Through the concept of geometrical factor, it is demonstrated that
the total signal, which measures the apparent conductivity, is the
summation of the partia1 products -geometrical factor by
conductivity - for the different regions of the ground under
consideration.

Log Presentation
 Resistivity logs are presented in Track 2 or in Tracks 2 and 3 combined on a log scale.
 It is possible to have data from both resistivity-type and induction-type tools shown
together, and in this case it is usual to convert the conductivity.
 readings from the induction devices to resistivities for display is also possible
(converting resistivities to conductivities for display) it is rarely seen).
 If the conductivity from induction-type logs is displayed, the units are millimho per
meter (mmho/m) and the scale is usually 0 – 2000 mmho/m (note the SI equivalent of
mmho/m is millisiemens per metre, mS/m).
5

Typical Log Response
 The induced current flowing in the formation induces a response in a receiver
coil in the tool.
 The response can be analyzed in terms of formation conductivity, the
reciprocal of resistivity.
 By adjusting the arrangement of the receiver coil, the formation resistivity
can be measured at a longer or shorter distance from the borehole.
 This gives two of the three independent resistivity measurements, a deep
reading and an intermediate reading.
7

C:UsersAbdur RaufDesktopUniversal.pptx
induction
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Induction Resistivity Log Measurement Tools
An apparatus for measuring conductivity of a geological formation adjacent
to a borehole comprising:
 a sonde adapted for traversing said borehole.
 an oscillator generating an output having a fundamental frequency
 An electrode transmitter and electrode receiver.
9

 a transmitter disposed within said sonde, said transmitter
comprising at least one coil and being coupled to said
oscillator, whereby the output of said oscillator is applied to
said transmitter for inducing eddy currents in said formation.
 a receiver disposed within said sonde, said receiver comprising
at least one coil for detecting said eddy currents in said
formation and inducing an electrical signal in said receiver.
10

Induction log Application
 Saturation determination
 Lithology identification
 Source Rock identification
 Locating of hydrocarbon bearing zones
 Correlation purposes
12

Background And Formula Of Induction log
 These logs were originally designed by Henry Doll of Schlumberger and
described in 1947.
 It is use in boreholes where the drilling fluid was very resistive (oil-based
muds or even gas).
 Induction logging is a controlled-source electromagnetic (CSEM) exploration
method.
 It characterizes geologic formations through the measurements of induced
magnetics fields. 14

 The sonde consists of 2 wire coils, a transmitter (Tx) and a receiver (Rx).
 High frequency alternating current (20 kHz) of constant amplitude is applied to
the transmitter coil.
 This gives rise to an alternating magnetic field around the sonde that induces
secondary currents in the formation.
 These currents flow in coaxial loops around the sonde, and in turn create their
own alternating magnetic field, which induces currents in the receiver coil of
the sonde.
 The received signal is measured, and its size is proportional to the conductivity
of the formation.
15

Interpretation of Induction Log
 Geophysical interpretation is a fundamental part of petroleum and mineral
exploration.
 The decision to drill for oil or minerals often depends on our ability to
obtain reliable models of the earth by using geophysical data gathered
at the earth’s surface or in boreholes.
 Interpretation involves determining the geologic significance of
geophysical data and generally integrates all available geologic and
geophysical information.
18

 Interpretation is a process of estimating an earth model whose response
is consistent with all available observations.
 Examples of geophysical observations might include seismic, gravity, magnetic, electrical,
electromagnetic, and borehole data.
 By this definition, interpretation can be considered a type
of geophysical inversion.
 The early electronic logs or e-logs, plotted only formation resistivity measurements.
 The resistivity of a rock is a measure of the degree to which it can impede the flow of an electronic
current.
 It is measured in ohm.m2/m which is usually referred to simply as ohm’s/m.
19

 The ability to conduct electrical current is a function of the conductivity
of the water contain in the pore space of the rock.
 Fresh water does not conduct electricity; however, the salt ions found in
most formation water do.
 Thus, unless that water is fresh, water-saturated rocks have high
conductivity and low resistivity, hydrocarbons, which are non conductive,
cause resistivity values to increase as the pore spaces within a rock
become more saturated with oil or gas.
20

REFERENCES
 Badea, E., M. E. Everett, G. A. Newman and O. Biro. (2001). Finite element
analysis of controlled-source electromagnetic induction using gauged
electromagnetic potentials, Geophysics 66, 786—799.
 Decker, K. T., M. E. Everett. (2009). Roughness of a layered geologic medium
and implications for interpretation of the transient electromagnetic response of a
loop source. SAGEEP 22, 188.
 Doll, H. G. (1949). Introduction to induction logging and application to logging
of wells drilled with oil base mud. Petroleum Development Technology:
Transactions of the American Institute of Mining and Metallurgical Engineers, 186,
148-162.

 Everett, M. E. (2013). Near-surface applied geophysics, Cambridge University
Press, New York, NY.
 Everett, M. E. (2009). Transient electromagnetic response of a loop source over
a rough geological medium, Geophysics 177, 421-429.
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Comparing Laterologs and Induction Logs
· Induction logs provide conductivity (that can be converted to resistivity).
· Laterologs provide resistivity (that can be converted to conductivity).
· Induction logs work best in wells with low conductivity fluids.
· Laterologs work best in wells with low resistivity fluids.
Both logs provide a range of depths of penetrations and vertical
resolutions. 25

 Induction log deep (ILD) is for the Rt Of the uninvaded zone.
 Induction log medium (ILM) For the sensitivity of the transitional
zone.
 V=IR
 R=rA/L
 Rwa=Rt/F
 Rwa=ILD/F (by replacing Rt into ILD)
 Rwa=Rw ( true resistivity of water)

Introduction to Induction Logging

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