A brief introduction of the resistivity logging important tool in the Petrophysical Interpretation.

2. Presentation
on
Resistivity Log
PRESENTED TO:
Prof. DR. SHAHID GHAZI
Presented By:
Hammad Ahmad Sheikh
BS Hons (4th Prof)

3. Contents
• Resistivity
• Factors Affecting Resistivity
• Introduction of resistivity log
• Principle of Resistivity Log
• Theoretical Consideration
• Invasion Zone
• Resistivity Tools
• Log Characteristics
• Principle uses
• Conclusion
• Refrences

4. Resistivity
• The resistivity (specific resistance) of a substance is the
resistance measured between opposite faces of a unit cube of that
substance at a specified temperature.
• The meter is the unit of length and the ohm is the unit of
electrical resistance. In abbreviated form, resistivity is
R = rA/L,
• Where R is resistivity in ohm-meters, r is resistance in ohms, A
is area in square meters, and L is length in meters.
• The units of resistivity are simply ohm-meters (ohm-m).
Conductivity is the reciprocal of resistivity

5. Factors Affecting Resistivity
Salinity of water
Porosity of the formation,
Lithology of the
formation
Degree of cementation,
Type and amount of clay
in the rock.
Fig 1.1 showing the response of resistivity
depending on the nature of fluid.

6. The resistivity log is a measurement of a formation's resistivity,
that is its resistance to the passage of an electric current. It is
measured by resistivity tools.
The resistivity of a formation is a key parameter in determining
hydrocarbon saturation. Electricity can pass through a
formation only because of the conductive water it contains.
With a few rare exceptions, such as metallic sulfide and
graphite, dry rock is a good electrical insulator.
.
Resistivity Log

7. Resistivity Log
Fig 1.2 showing the response of resistivity curve in the different formations.

8. 2. Principle of Resistivity Log
• The basic resistivity tool arrangement was provided
by conard schulmberger in 1927.
• Currents were passed through the formation by means
of current electrodes, and voltages were measured
between electrodes. These measured voltages
provided the resistivity determinations for each
device.

9. Principle of Resistivity Log
Fig 1.3 showing the different tools to measure the resstivty.

10. 3. THEORETICAL CONSIERATIONS
• 3.1. Earth resistivity and conductivity
• 3.2. Rock resistivity
• 3.3. Resistivity of clays

11. 3.1 EARTH RESISTIVITY AND
CONDUCTIVITY
• Two tests can be applied under subsurface conditions
to measure resistivity.
• The first test is a direct measurement. A current is
passed between two electrodes on a logging tool and
the potential drop between them provides the
resistivity.

12. 3.1 EARTH RESISTIVITY AND
CONDUCTIVITY
• The second test is indirect in that it measures
conductivity. A current is induced in the formation
around the borehole and the capacity to carry the
current is observed. This carrying capacity is the
conductivity. The resistivity is simply the reciprocal
of the conductivity

13. RESISTIVITY VS CONDUCTIVITY
Fig 1.4 showing the relationship between Resistivity and conductivity.

14. 3.2 ROCK RESISTIVIY
• It is only the formation waters that are conductive, the
conductivity of the rock in general should be that of the
solution it contains. Although the rock plays no active part, it
plays an important passive one .
• This passive role is basically dependent on rock texture or
more specifically on the geometry of the pores and pore
connections in rocks, the easier the path through the pores the
more current that passes.

15. ROCK RESISTIVIY
Fig 1.5 showing the rock resistivity depending upon the conductance.

16. 3.3 RESISTIVITY OF CLAYS
• Clays conduct electricity in two ways, through pore
water and through the clay itself.
• The porosity in clay, like that in other rocks, encloses
conductive formation water.

17. 4. ZONE OF INVASION AND
RESISTIVITY
• It is all-important to the understanding of borehole resistivity.
The essential target of resistivity logging is that of the true
resistivity of the formation (R,) and, especially, its saturation in
hydrocarbons.
• To this effect, it is necessary to consider the invasion of mud
filtrate (with a certain salinity and hence resistivity, Rmf) into
a formation containing either formation water (resistivity Rw)
or hydrocarbons.

18. ZONE OF INVASION AND
RESISTIVITY
Fig 1.6 showing the zone of invasion and resistivity

19. Tools used in Invasion
Uninvaded Zone Transition
Zone
Flushed Zone Mud
Cake
This zone is also
called as virgin
Zone.
The zone
where the
drilling fluid
and formation
fluid is
intermixed
with each
other.
This zone is
totally comprises
of drilling fluid.
The zone is
made up of
bentonite
clay which is
present in the
drilling fluid.
SFL
MSFL
M
LLL
LLd

20. Resistivity Tool

21. 5.RESISTIVITY TOOLS
5.1.Unfocused devices
(5.1.1 ) Normal log
(5.1.2) Lateral
5.2 Focused Devices
Laterolog LL3
Laterolog LL7
Dual Laterolog
SFL
5.3 Micro-Resistivity Devices
Types of Micro-Resistivity Log
Fig 1.7 showing the Focused and Non
focused electrical logs.

22. Unfocused Devices
• Normal devices:
o In this arrangement a constant
known current is flowed from
A to B (or B to A), and the
potential is measured between
M and N.
o Electrode B and N are kept at
a long distance from
electrodes A and M to provide
quasi-infinite reference points
for the current and potential
measurements. Fig 1.8 Showing the standard normal
configuration.

23. Unfocused Devices
• Lateral Log
o In the lateral device a
constant current is passed
between A and B.
o The potential difference
M and N is measured
Fig 1.9 showing the electric configuration
of Lateral Log.

24. 5.2 Focused Devices
Fig1.10 showing the electrode
configuration of LL3
Laterolog LL3
• The LL3 has 3 current
emitting electrodes.
• The middle one, emits the
main current while the either
side of electrodes also emits
a current.
• This helps to keep the central
electrode more focused.

25. Focused Devices
Laterolog LL7
• The LL7 has 7 electrodes.
• A constant current is emitted from
the centre electrode.
• A bucking current is emitted from
the two far electrodes.
• The two pairs of monitoring
electrodes are brought to the same
potential difference.
• This electrode arrangement
produces a thin disk of current that
is confined between the two sets
of measuring electrodes.
Fig 1.11 showing the LL7 tool
configuration.

26. Focused Devices
Fig 1.12 showing the electrode configuration of Dual Laterolog LLd and LLs

27. Focussed devices
The Spherically Focused Log
• The SFL device measures the
conductivity of the formation
near the borehole.
• In this the current is focussed
quasi-spherically.
• It is useful as it is sensitive
only to the resistivity of the
invaded zone.
Fig 1.13 showing the electrode
configuration of SFL/

28. 5.3 Micro-Resistivity Log
Fig 1.14 showing the electrode
configuration of Microlog.
The Microlog
• The microlog(ML) is a rubber
pad with three button
electrodes placed in a line.
• A known current is emitted
from electrode A.
• The potential differences
between electrodes M1and M2
and between M2 and a surface
electrode are measured.

29. Types of Micro-Resistivity Log
Fig 1.16 Micro-
Spherically Focused
Log
Fig 1.15 Micro-Laterolog
Fig 1.17 Proximity
Log
These devices have same sort of electronic configuration.
These have electrode spacing of a few inches.
They penetrate the formation to a very small degree.

30. 6. Log characteristics
• 6.1 Log format and scales
• 6.2 Depth of investigation
• 6.3 Bed resolution

31. 6.1 scales
• Providing scale is a common problem in all resistivity
devices that can be read accurately over the full range
of response.
• There are two types of scales on which resistivity
curve are recorded.
o Hybrid scales
o Logarithimic Scales

32. Types of Scales
Fig(1.18) showing the Hybrid Scale Fig(1.19) showing Logarithmic Scale

33. 6.2 Depth of investigation
• Depth of investigation also has geological significance. The
logs from deep-reading devices, are best used for gross
formation characteristics in which individual beds are
unimportant.
• Texture-related changes are best seen on the logs from tools
mainly influenced by the invaded zone.

34. 6.3 Bed resolution
The resistivity tools are capable of very fine bed resolution, the
finest of all the logging tools.
The micro tool logs give too fine a resolution for practical,
usable, geological bed resolutions. The logs are best used for
defining bedding characteristics.
The laterologs resolve beds at the right scale for bed-boundary
indications , but they should be used in conjunction with the
other logs.
.

35. 6.3 Bed resolution
Fig 1.20 showing the bed
resolution determined by MSFL.

36. 7. Principal uses

37. 7.1 Quantitative uses of the resistivity
logs
• The quantitative use of log resistivity measurements
is at the heart of the whole domain of quantitative
well-log interpretation - the domain of petrophysics.
• The principal use of well logs is to detect oil: the
principal use of the resistivity log is to quantify oil
(and of course, gas).

38. 7.2 Qualitative uses of resistivity
7.21.Texture and facies
The simplest relationship
between resistivity and
texture is demonstrated by
an increase in resistivity as
porosity decrease.
Fig 1.21 showing the facies change marked by
resistivity curve.

39. Lithology
Fig 1.22 showing the lithology change.
• Resistivity log can be used
for the lithology
identification purposes.
• Tight limestone's shows
high resistivity.

40. Lithology
Fig 1.23 showng the difference
between Shale and sand sequences
• Resistivity logs can best
recognize the shale and sand
sequences.
• Sand shows relatively less
resistivity values as
compared to shale.

41. Correlation
Fig 1.24 showing the correlation.
• Resistivity log can be used
for correlating the
subsurface data on the basis
of same resistivity curve.
• The best tool to acquire the
data is deep induction tool.

42. Correlation
Fig 1.25 showing the
pay zone marked by
reisitivity curve.

43. Permeability
Fig 1.26 showing the permeability of a
rock.
• Resistivity logs can be
used to find out the
permeability of a rock
unit in the subsurface.

44. 7.2.3 Source-rock investigation:
The resistivity log may be used both qualitatively and
quantitatively to investigate source rock.
The effect of a source rock has on the resistivity log depends on
the maturity of the organic matter.
Fig 1.27 showing the matureness on the basis of resistivity curve.

45. Conclusions
• Resistivity logs are helpful in determining the porosity of a
rock.
• Used in the search of hydrocarbons.
• Find out the quantity of hydrocarbons is present in the
subsurface.
• Bed resolution can be noted by this log.
• Used for correlating the data of different wells on the basis of
resistivity curves.
• Lithology Indicator.

46. 8. REFERENCES
• Selley,R.C.(1995) Elements of Petroleum Geology.2nd
ed.London.Academic Press P 57-60
• Serra, o.(1988) fundamentals of well log interpretation. 3rd ed.
New York Elsevier science Publishers P 51-76.
• Rider, H.(2002) The geological interpretation of well logs. 2nd
ed. Scotland. Rider French consulting Ltd P 35-48.
• Schlumberger Log Interpretation and principles