1. Institute of Petroleum Exploration 9, Kaulagarh Road, Dehradun
Keshav Deva Malaviya
Institute of Petroleum Exploration
9, Kaulagarh Road, Dehradun
Ph: , 6370, 5681
Well Logging
M.K.Tewari
D.G.M. (wells) ONGC KDMIPE Dehradun

2. ELECTROMAGNETIC EFFECTS
The electromagnetic properties of a material that effect E-M tools log responses are:
e (eR) = Dielectric Constant
s = Conductivity
m = Magnetic Permeability

3. The NEW Tool operates at 32 kHz and 8 kHz
In the lower frequency range (around 20 kHz) the conductivity effect dominates the tool response

4. The (High Frequency Tool) operates at 1 GHz (1000 MHz)
In the mid frequency range (around 20 MHz) both conductivity and dielectric effects are significant
In the higher frequency range (around 1GHz) the dielectric effect dominates the tool response
The (High Frequency Tool) operates at 1 GHz (1000 MHz)

5. Comparison between the HRI and the HFDT

6. Induction tools measure formation conductivity by inducing a current flow within the formation

7. Induction Tools (DIL, HRI, HRAI)
Measure the resistivity of the formation by inducing current flow R
V  R
Uses Electromagnetic forces to induce current flow in formation
Do not require conductive medium in borehole T
Can be run in freshwater muds, air-filled holes, and oil-based muds
Can provide measurements at different depths of investigation

8. Faraday's Magnetic Field Induction Experiment

9. Induction tool
Induction tools are based on principles of electromagnetic induction.
A magnetic field is generated by an AC electrical current flowing in a continuous loop.
An AC electrical current is generated when a continuous loop is subjected to a magnetic flux.
The magnitude of this current is proportional to the conductivity of the continuous loop

10. Induction tool
Lets consider a simple induction tool with one transmitter coil and one receiver coil,
Applying signal to the transmitter coil it create a magnetic field and induce a current directly in the receiver coil.
The signal in the receiver coil is 90 degrees out of phase to the transmitter signal

11. Induction tool
The magnetic field generates current loops in the formation because the conductivity of the formation,
those loops are in the same axis of the tool and
the current is 90 degrees out of face to the transmitted signal

12. Induction tool
The current flowing through the ground loops generates a secondary magnetic field
This secondary magnetic field induces a current in the receiver coil with 90 degrees out of phase with respect to the ground loops and 180 degrees out of phase with respect to the transmitted signal.

13. Induction tool
The received current is proportional to the conductivity of the formation in the loop.
The constant of proportionality varies with the radius and position of the loop along the tool axis, as well as the position and construction of the coils.
This constant of proportionality is the geometric factor.

14. Induction Measurement Principle
E = K.g.C

15. Real and Quadrature signals
From this model it can also be deduced that the received signal has undergone two 90-degree phase shifts with respect to the current in the transmitter.
It is therefore back in-phase with this current. (In fact, it is 180 degrees out-of-phase, but this is treated as in-phase with a sign change).

16. Real and Quadrature signals
This in-phase signal is usually called the "Real Signal." This phase relationship is convenient because there is also a signal in the receiver that is coupled directly from the transmitter.
This signal is large, but unaffected by the formation conductivity. This signal is called the "direct-coupled" or "Mutual Signal."
This signal is 90 degrees out-of-phase with the transmitter current, so it can be separated from the desired in phase signal by using phase-sensitive detection.

17. Real and Quadrature signals
There is also a signal which is 90 degrees out-of-phase with the current, which is affected by the formation conductivity. This is called the "Quadrature Signal."

18. Signal Phase with respect to IT (transmitter current)
X, XE
VR ,RE
VX¢ 0°
90°
180°
270°

19. THE GENERAL INDUCTION RESPONSE
is the skin effect correction

20. SKIN EFFECT δ = (2/μώσ)½ = skin depth σ = formation conductivity
L = spacing between transmitter and receiver
K=tool constant
ώ= Tool frequency

21. SKIN EFFECT SKIN EFFECT CORRECTION DESIRED RESPONSE
ACTUAL CONDUCTIVITY(mmhos/m)
APPARENT CONDUCTIVITY AS SEEN BY TOOL(mmhos/m)
DESIRED RESPONSE
SKIN EFFECT CORRECTION

22. SKIN EFFECT SKIN EFFECT µ f 1/2 SKIN EFFECT µ s1/2 SKIN EFFECT µ L
THE TERM SKIN EFFECT COMES FROM THE WELL- KNOWN PHENOMENON IN METALLIC CONDUCTORS IN WHICH A HIGH FREQUENCY ALTERNATING CURRENT TENDS TO FLOW IN THE OUTER MOST PART, THE SKIN, OF THE CONDUCTOR .
SKIN EFFECT µ f 1/2
SKIN EFFECT µ s1/2
SKIN EFFECT µ L

23. Induction logs run in very large holes Induction logs run in salt muds
DEEP INDUCTION AND RT
In 90% of the cases, it is permissible to assume that the deep induction reading is equal to Rt. Conditions where this assumption is not valid include:
Induction logs run in very large holes
Induction logs run in salt muds
Places where the bed of interest is thin
Where the shoulder-bed resistivity is markedly different from the resistivity of the bed under consideration
Where invasion is abnormally deep

24. DUAL INDUCTION TOOL VERTICAL RESOLUTION DEPTH OF INVESTIGATION
DEEP FEET
MEDIUM FEET
SHORT GUARD INCHES
DEPTH OF INVESTIGATION
DEEP FEET
MEDIUM FEET
SHORT GUARD INCHES

25. HIGH RESOLUTION INDUCTION TOOL
VERTICAL RESOLUTION
DEEP FEET
MEDIUM FEET
DFL--- < 17 INCHES
DEPTH OF INVESTIGATION
DEEP FEET
MEDIUM FEET
DFL INCHES

27. THE FIRST LOGGING OPERATION
PECHELBRON FRANCE 1927

28. THE FIRST LOG (1927)
RESISTIVITY
DEPTH

29. Conclusions drawn from the first logging job were
Hard formation layers appeared on the diagrams as peaks
Contrasting clearly with the soft and conductive marls (sands).
When the log results were confirmed by actual physical core samples,
electrical coring was firmly established as a valuable tool for geological surveys

30. Spontaneous potential
Even with no current emitted in the borehole by their tool, a potential difference was measured across a pair of monitor electrodes on the sonde. After integrating this self potential [called the Spontaneous Potential (SP)]
The SP is a natural occurring potential relative to a surface potential measured in the borehole mud.
Uses Of The SP
1. Determine values of formation water resistivity
2. Define bed boundaries
3. Identify permeable zones
4. Qualitative indication of shale content
5. Well to well correlation

31. Electrode Tools (DLLT)
Measure the formation resistivity by injecting current into the formation CR
Current moves from source to current return
Current is focused so travels through the formation to the current return
Require conductive medium in borehole (saltwater mud)
Can not be run in air-filled holes, and oil-based muds
Provides different depths of investigation

32. Unfocused Log
The simplest measurement of the resistivity of the formation can be done placing a current emitting electrode downhole and a return electrode at the surface, at surface we can measure the current applied and the voltage to calculate the resistivity.
This configuration measures the sum of all the resistances between the surface electrode and the downhole electrode.

33. Focused Log
In highly resistive formations or in very low-resistivity muds, the unfocused electric log does not work very well.
The mud column tends to short-circuit the current of the electric log, causing the readings to be too low and lacking in definition.

34. Focused Log
In order to measure the resistivity of the formation the measure current must be forced to flow in the formation.
This is known as focusing.
The tools using this technique are called Laterolog devices.
The term laterolog came about because the current is forced to flow "laterally" away from the tool.

35. Focused Log

36. Focused Log

37. DEPTH OF INVESTIGATION
DUAL LATEROLOG TOOL
VERTICAL RESOLUTION
DEEP FEET
MEDIUM FEET
MICROGUARD (MGRD) INCH
MSFL INCHES
DEPTH OF INVESTIGATION
DEEP FEET
MEDIUM FEET
MICROGUARD (MGRD) IN
MSFL INCHES

38. Introduction
In a laterolog-type system, the measure current is forced to flow perpendicular to the borehole (in a `lateral' direction) by the potential lines created by the focusing currents emitted by the electrodes surrounding the central current measure electrode.

39. Introduction
The thickness of this measure current beam (and the extent to which it maintains this beam shape) represents an equivalent resistor.
The voltage drop across this resistor and the current through are the actual measurements from the tool.

40. Introduction
Knowing the voltage (E) and current (I), the resistor can be easily calculated (R=E/I).
Once the apparent resistor (Rapp) is known, apparent resistivity (rapp) can be determined since r=R .A/L where
A represents the “area” and
L represents the “length” of the “resistor.”
The factor A/L is referred to as the tool “k factor.”

41. Log Presentation

42. Microlaterolog
The microlaterolog tool is a focused device designed to measuring flushed zone resistivity.
The standard MLL pad is a 9 button fluid filled pad.
The center button is the measure electrode and
the remaining buttons form the guard and are all connected together.

43. Microlaterolog MSFL/MLL
GUARD
ELECTRODES
CENTER
ELECTRODE
MSFL/MLL PAD
GUARD
ELECTRODES
CENTER
ELECTRODE
MSFL/MLL PAD

44. Shallow Micro resistivity log devices

45. Nuclear Tools

47. GAMMA RAY ORIGIN
Gamma rays originate from the decay of radioactive elements. In most formations, these elements are isotopes of Potassium, Uranium, and Thorium.

49. PARENT (P) TO DAUGHTER (D) DECAY SEQUENCE
NATURAL DECAY MODES
EMITS ALPHA
EMITS ELECTRON
EMITS POSITRON
CAPTURES ELECTRON
PARENT
DAUGHTER
PARENT (P) TO DAUGHTER (D) DECAY SEQUENCE

50. ALPHA DECAY
BETA - ELECTRON DECAY
BETA - POSITRON DECAY
BETA - ELECTRON CAPTURE

51. GAMMA EMMISION
g = GAMMA RAY

52. POTASSIUM DECAY
Eg = EU-EL

53. THALLIUM DECAY Tl

54. The commonly used multiples of this unit are kiloelectron volts, keV, and Megaelectron volts, MeV. These represent multiples of 1,000 and 1,000,000 electron volts, respectively. Therefore, a gamma ray with an energy of 1 MeV would have the same striking power as an electron accelerated through a 1,000,000 volt potential.
ELECTRON VOLT

55. BASIC GR BLOCK DIAGRAM SCINTILLATIONCRYSTAL PM TUBE DISCRIMINATOR
12 BIT COUNTER
BGO
NaI
CsI

56. SCINTILLATION DETECTORS
GAMMA RAYS INTERACT WITH SCINTILLATION CRYSTAL (COMPTON, PHOTOELECTRIC, PAIR PRODUCTION) PRODUCING ELECTRONS.
ELECTRONS EXCITE PHOSPHOR ATOMS, WHICH IN TURN, DECAY BY EMISSION OF LIGHT.
THESE PHOTONS INTERACT WITH THE PHOTOCATHODE OF THE P.M. TUBE. PRODUCING ELECTRONS.
EJECTED ELECTRONS ARE FOCUSSED INTO PHOTOMULTIPLIER STRING.
ELECTRONS ARE ACCELERATED THROUGH SUCCESSIVE DYNODES, PRODUCING MULTIPLICATION AT ANODE (1 e- = 106 e-)

57. APPLICATIONS OF THE NATURAL GAMMA RAY TOOL
CORRELATION
BED BOUNDARIES
VOLUME OF SHALE
LITHOLOGY INDICATOR
DEPTH CONTROL

58. API UNITS Shaly sand Shale Very shaly sand Clean limestone Dolomite
GAMMA RAY RESPONSE FOR TYPICAL FORMATIONS 50
100
API UNITS
Shaly sand
Shale
Very shaly sand
Clean limestone
Dolomite
Clean sand
Coal
Anhydrite
Salt
Volcanic ash
Gypsum

59. 150
API
GR shale
GAMMA VOLUME OF SHALE PARAMETERS
GR log
GR clean

60. VOLUME OF SHALE FROM GAMMA RAY LOGS
RELATIONSHIP
EQUATION
Linear
Clavier
Steiber

61. VOLUME OF SHALE CALCULATIONS
SP Method
Here,fN and fD are the neutron and density porosities in the shaly zone, fNsh and fDsh are the values in a nearby shale.
GR Method
ND Method

63. Introduction The Density measures: formation bulk density (rb)
and photoelectric absorption index (Pe)
of the lithologic column cut by the borehole.

64. Introduction
The term rb is applied to the overall density of a unit volume of rock.
In the case of porous rocks, it includes the
density of the fluid in the pore spaces
as well as the grain density of the rock.

65. Introduction
Pe is dependent on Z, the atomic number, of the material being measured and is used to identify lithology.

66. Density Tool The Density utilizes a
Cesium 137 (Cs137) gamma ray source
two Sodium Iodide scintillation detectors
and a small Cesium 137 gamma ray source beside the ls detector
all of which are mounted on an articulated pad.

67. Density Tool
To measure rb and Pe, a beam of gamma rays is directed into the rock.
The detectors at fixed distances from the source measure changes in the intensity of the gamma ray flux resulting from the
scattering and
absorption effects of the formation.
The higher the formation density, the lower the intensity of gamma radiation at the detectors.

68. Density Tool The tools primary applications are:
Measure bulk density,
Lithology determination using Pe,
Correlation.
The tools main limitations are:
Primarily open hole application,
Limited cased hole applications,
Maximum hole diameter 22 inches,
Minimum hole diameter 6 inches.

69. Eg >1.02 MeV e- e+ PAIR PRODUCTION ELECTRON
POSITRON
INCIDENT HIGH ENERGY PHOTON e- e+

70. e- COMPTON SCATTERING 10 MeV > Eg >100KeV SCATTERED PHOTON
INCIDENT PHOTON
SCATTERED PHOTON
COMPTON RECOIL ELECTRON e-
10 MeV > Eg >100KeV

71. PHOTOELECTRIC EFFECT
INCIDENT PHOTON
ELECTRON e-
Eg 100KeV

72. Density Tool
Interactions due to Compton scattering are used in the measurement of
bulk density,
and those due to Photoelectric absorption used to
determine Pe.

73. Density Tool
The Density tool has two detectors which are set at different distances from the source,
with the one nearest designated the short spaced detector (SS)
and the other the long spaced detector (LS).

74. Density Tool
The long spaced detector is configured to measure gamma rays associated with both:
Compton scattering and
Photoelectric absorption effects.
Therefore the LS detector count rates are used in the determination of both
bulk density and Pe.

75. Density Tool
As with any other nuclear logging instrument, the depth of investigation of the Density is shallow.
For this reason,
mud cake and
borehole rugosity
can have an appreciable effect on the total measurement, despite the fact that the Density is a contact device.

76. Density Tool To compensate for these effects
which occur when any material other than formation intervenes between the pad containing the detectors and source and the formation itself,
a two–detector arrangement is used.

77. MUD
MUD CAKE
FORMATION
THE DENSITY TOOL

78. + ¥ (662) Radioactive cesium as a logging source is used.
Cesium emits beta particles(which do not escape the stainless steel source case) and gamma rays.
These gamma rays have an initial energy of 662 KeV and, due to the fact
they have zero charge, can penetrate deeply into the formation.
The cesium source strength is 1.5 Curies and it has a half-life of 33 years.

79. Ne= Electron Density

80. COUNT RATE AT A DETECTOR
This equation assumes the gamma rays can follow a straight line path from source to detector.

81. therefore we can write the equation as:
taking the log of both sides, and considering a constant :

82. Density Tool
Electron density is the number of electrons per unit volume.
There is a direct relationship between electron and bulk density.
For practical purposes a normalized “electronic” density is defined by the equation:

83. Density Tool

84. Density Tool
The idealization that Z/A=0.5 for all elements of interest during logging operations was optimized by use of test pit calibrations.

86. Z/A FOR COMMON DOWNHOLE ELEMENTS

87. HYDROGEN CALIBRATION For water (H2O) For Limestone( CaCO3 )
Tool must be calibrated for rhoe in water=1.1101
Rhoe in limestone=2.7076
Linear conversion rhoeA=G+H rhoe

88. FOR FRESH WATER FILLED LIMESTONES
Solving the two equations and two unknowns we obtain the accepted industry standard for calibrated density tools
Since all density tools are calibrated to match the response of some standard tool
calibrated to read the true bulk density values of pure, fresh water filled limestone
formation of varying porosities (usually from 0 to 40%), the response of all density tools is given by equation above

89. Porosity Porosity is one of the most important reservoir parameters.
This is the fractional volume of the rock representing the pore spaces between the rock grains which contain reservoir fluids.
Its accurate determination enables a more precise calculation of reserves and production potential of a reservoir.

90. Porosity
The bulk density measured by the instrument is the volumetric average of the densities of all the rock components:

91. Examples

93. NEUTRON TOOLS EPITHERMAL THERMAL PULSED NEUTRON TMD TMD-L PSGT RMT
Spectral Flow

94. CLASSIFICATIONS OF NEUTRONS
HIGH ENERGY
FAST
INTERMEDIATE
EPITHERMAL
THERMAL

95. NEUTRON SOURCE

96. KE BEFORE ¹ KE AFTER (RECOIL) + KE AFTER (SCATT)
INELASTIC SCATTERING
INELASTIC GAMMA RAYS
KE BEFORE ¹ KE AFTER (RECOIL) + KE AFTER (SCATT)

97. ELASTIC SCATTERING q = SCATTERING ANGLE e = RECOIL ANGLE
INCIDENT NEUTRON
SCATTERED NEUTRON
RECOIL NUCLEUS
q = SCATTERING ANGLE
e = RECOIL ANGLE
KE BEFORE = KE AFTER (RECOIL) + KE AFTER (SCATT)

98. ELASTIC HEAD-ON COLLISION
M = Mass of struck nucleus in AMU
M = 1, for protons or neutrons
(FE)max loss = Maximum fractional energy loss of neutron

99. MAXIMUM FRACTIONAL ENERGY LOSS

100. CROSS SECTION
The term "Cross Section" can be thought of as a measure of the probability that a nuclear event will occur between a particle and a target.
Cross section is usually expressed in terms of the effective area which a single target presents to the incoming particle

101. CROSS SECTIONS
SLOWING DOWN CROSS SECTION
CAPTURE CROSS SECTION

102. HYDROGEN INDEX
It is more correct to refer to the Neutron derived porosity as a Hydrogen Index, since the porosity is indirectly measured through the evaluation of hydrogen content.

103. HYDROGEN EFFECT ON NEUTRON TOOLS
In a formation with large amount of hydrogen, source neutrons will be slowed more quickly than in formation with little hydrogen.
HIGH HYDROGEN CONTENT = LOW COUNTS

104. CHARACTERISTIC LENGTHS
* Total Migration Length (M): (crudely speaking) the square of the three characteristic lengths squared:
M 2 = (Ls )2 + (Le )2 + (Lt )2
This length can be considered (crudely again) the total average distance the neutron travels from source to capture.
* Thermalizing Length (Le) : (crudely speaking) the average distance travelled by a neutron in going from an energy value of 1.46 eV to eV.
* Slowing Down Length (Ls ) : (crudely speaking) the average distance traveled by a fast neutron in going from the source energy at 4.6MeV to the energy level of 1.46eV. Ls is mainly a function of hydrogen concentration.
* Thermal Diffusion Length (Lt ) : (crudely speaking) the average distance the neutron travels from the point it first reaches the thermal level at eV to its capture still at the thermal level (0.025 eV). Lt is a function, not only of the hydrogen content, but of the concentration of elements with high capture cross section, (e.g. chlorine).

105. DEPTH OF INVESTIGATION 8 TO 12 INCHES
VERTICAL RESOLUTION
24 INCHES
DEPTH OF INVESTIGATION
8 TO 12 INCHES

106. FORMATION ENVIRONMENTAL EFFECTS ON THE NEUTRON POROSITY
LITHOLOGY EFFECT
SHALE EFFECT
GAS EFFECT

107. LITHOLOGY EFFECT
Different formation types have different abilities to slow down and capture neutrons. This makes our neutron porosity lithology dependent.

108. NEUTRON SLOWING DOWN LENGTHS

109. SHALE EFFECT
The neutron tool, responding to the total amount of hydrogen in the form of water, will consider the volume occupied by both bound and free water as porosity in shales. Since the bound water is structurally and chemically bonded to the shale, the neutron porosity reads too high.
Shales can also have unusually large thermal neutron capture cross sections ( e.g. Boron). This makes thermal neutron tools read even higher for the porosity.

110. NEUTRON SHALE CORRECTION
Here fneutron-shale is the neutron porosity in a nearby shale

111. GAS EFFECT
Because of the low amount of hydrogen in gas, the neutron tool sees gas as fresh water occupying a smaller volume than the actual volume present. The porosity therefore reads too low.
Also the excavation effect - which states simply that gas in the rock will cause less rock material to be present to slow down, scatter, or absorb the neutrons - will cause the porosity to appear even lower.

113. Thanks