Open Hole Electrical Logging
Lecture Presentation
October 18, 21, and 23, 2002
Carlos Torres-Verdín, Ph.D.
Assistant Professor
PGE368
Fall 2002 Semester
Objectives:
•To understand the physical principles behind the
operation of laterolog and induction tools,
• To understand the principles behind the
interpretation of apparent resistivity curves
acquired with laterolog and induction tools,
• To understand the importance of environmental
corrections, and
• To introduce the physical principles behind the
operation of LWD resistivity tools.
1
Complementary Reading Assignments:
1. Bassiouni, Z., 1994, Theory, Measurement, and
Interpretation of Well Logs, Chapter 5: “Resistivity
Logs.”
2. Schlumberger’s Computer Animated Presentations
on Induction Principles and Laterolog Principles
available from our course web site.
Open Hole
Borehole
Environment
2
Open-Hole Logging Environment
Dynamic Mud Filtrate Invasion and Mud Cake Buildup
Source: Oilfield Review, Schlumberger
LABORATORY SAMPLE
Brine-Water Saturation
V
+ -
I
R
+
+
+
+
V
R=
I
3
ELECTRICAL LOGGING TOOLS
Induction
Galvanic (Laterolog)
Low Frequency Excitation: 10 Hz – 500 KHz
ELECTRICAL LOGGING TOOLS
Induction
Laterolog
Electrical Conductivity of Mud is an Important Issue
4
Logging Tools
RESISTIVITY
LATEROLOG
40 cm
NEUTRON
RADIOACTIVITY
GAMMA RAY
DENSITY
ACOUSTIC
SONIC
MICRO RESISTIVITY
RESISTIVITY
MICROLOG
DIPMETER
250 cm
200
150
100
80 cm
50
30 cm
20 cm
RESOLUTION
80 cm
INDUCTION LOG
60 cm
5 cm
2 cm
0 cm
0 cm
DEPTH OF INVESTIGATION
INDUCTION
vs.
LATEROLOG,
When?
5
NORMAL MEASUREMENT IN A BOREHOLE
Resistivity in a Homogeneous Medium
Current lines
Equipotential
spheres
RI

 − dV = 4 π r 2 dr

∞
dr
RI

V = ∫ RI
=
2

4π r
4π r
r

V

R = 4π r

I

dV 4 π r 2
R = −

dr
I

6
LATERAL MEASUREMENT
GUARDED ELECTRODE MEASUREMENT
7
16” Short Normal - 1979
•
•
•
•
–
–
–
–
1927: 1st wireline resistivity
1st resistivity while drilling
Rapparent = G V/I
Requires conductive, waterbased drilling fluid
Large borehole effects limit
range Rb < R < 20 Rb
Low quality suitable for
correlation and resistivity trends
Insulation prone to failure
Obsolete technology
LATEROLOG 7
8
DUAL LATEROLOG
LATEROLOG
(GALVANIC)
TOOLS
9
LATEROLOG
TOOL CONFIGURATION
ACTUAL TOOL
ELECTRICAL CONDUCTION PHENOMENA
Laterolog Tools
10
LATEROLOG TOOL
Different Current Focusing Strategies
LLD CORRECTION CHART
FOR BOREHOLE EFFECTS
11
LLD
CORRECTION CHART
FOR
INVASION EFFECTS
LLD CORRECTION CHART
FOR BED THICKNESS
12
LLS CORRECTION CHART
FOR BED THICKNESS
MICRO
LATEROLOG
DEVICE:
a
Pad Tool
13
MSFL TOOL:
a
Micro-Laterolog
Device
FORMATION MICRO-IMAGING TOOL
14
PHYSICAL
PRINCIPLE OF
INDUCTION
TOOLS
PHYSICAL PRINCIPLE OF INDUCTION TOOLS
15
INDUCTION SOUNDING
PHYSICAL PRINCIPLE OF INDUCTION TOOLS
16
Dual Phasor
Array Induction
Multi-Frequency Acquisition
PRINCIPLE OF INDUCTION FOCUSING
17
INDUCTION TOOL SENSITIVITY
Ideal Radial
Geometric Factors
Actual Radial
Geometric Factors
18
SENSITIVITIES FOR DIFFERENT COIL SUBARRAYS
LINEAR APPROXIMATION THEORY
(Geometric Factor Approximation)
19
FOCUSED SENSITIVITY FUNCTIONS
SKIN EFFECT CORRECTION
(Correction for Frequency-Dependent
Propagation Effects)
20
BOREHOLE CORRECTION
(Correction for Mud Conductivity
And Borehole Size)
BOREHOLE CORRECTION
(Correction for Mud Conductivity And Borehole Size)
21
BED THICKNESS CORRECTION
(Induction Log)
INVASION
CORRECTION
(Induction Log)
22
SUMMARY
Approximate Interpretation Cycle
EXAMPLE
Skin and Borehole Corrected Induction Curves
23
EXAMPLE
Focused Induction Curves
MODERN INTERPRETATION TECHNIQUES
24
COMPREHENSIVE
INTERPRETATION PROCESS
(Numerical Simulation and
Inversion)
EXAMPLE
2-D Inversion Results
25
LWD
RESISTIVITY TOOLS
16” Short Normal - 1979
•
•
•
•
–
–
–
–
1927: 1st wireline resistivity
1st resistivity while drilling
Rapparent = G V/I
Requires conductive, waterbased drilling fluid
Large borehole effects limit
range Rb < R < 20 Rb
Low quality suitable for
correlation and resistivity trends
Insulation prone to failure
Obsolete technology
26
2 MHz Propagation - 1984
• 1967 patent by M.
Gouilloud
• Transverse E-field
• Works in conductive or
insulating drilling fluids
• Small borehole effects in
smooth boreholes
• 1st quantitative LWD
resistivity measurement
• ~0.1 – 200 ohm-m range
2 MHz Propagation - 1988
• Symmetric array
- increased accuracy
- reduced effects in rugose
holes
• Two resistivities derived
from Phase Shift and
Attenuation
• Dual radial depths-ofinvestigation
• Anisotropic formations
27
Close-Up of Tool
Loop antennas located under slotted metal shields.
Dual
Depths
• Phase Shift
provides a shallow
resistivity with high
axial resolution
• Attenuation
provides a deep
resistivity with
lower axial
resolution
28
Advances in Propagation
Resistivity
•
•
•
•
1991 – Array with 4 depths-of-investigation
1995 – Array with 10 depths-of-investigation
1995 – Dual frequencies 400 kHz and 2 MHz
Different size drill collars (3” to 9” OD)
1993: Toroidal Resistivity
• Electrodes held at collar potential
& currents measured
• Improves S/N, dynamic range &
provides high spatial resolution
• 1st azimuthal resistivity
• Provides borehole images and dip
• Multiple depths-of-investigation
• Active focusing technique
• 0.1-20,000 ohm-m range
• Minimal borehole effects
Rb < R < 100,000 Rb
29
6.75” Toroidal Resistivity
Toroid
Buttons
Ring Toroid
Location of drill bit
Borehole Resistivity Imaging
• Each button scans 360°
as collar rotates
• Stacked scans provide
continuous image
• Geological features:
–
–
–
–
Beds
Dipping formations
Fractures
Faults
• Geosteering
30
Acknowledgements
• Schlumberger
• Baker Atlas
• Repsol-YPF
31