Electrical Logging Principles

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Open Hole Electrical Logging

Lecture Presentation

October 18, 21, and 23, 2002

Carlos Torres-Verdn, 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.


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Complementary Reading Assignments:

1. Bassiouni, Z., 1994, Theory, Measurement, and

Interpretation of Well Logs, Chapter 5: Resistivity

Logs.

2. Schlumbergers Computer Animated Presentations

on Induction Principles and Laterolog Principles

available from our course web site.

Open Hole

Borehole

Environment


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Open-Hole Logging Environment

Dynamic Mud Filtrate Invasion and Mud Cake Buildup

Source: Oilfield Review, Schlumberger

LABORATORY SAMPLE

Brine-Water Saturation

+ -

++

++

--

--

VI

R =V

I

R


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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


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250 cm 200 150 100 50 0 cm

80 cm

80 cm

40 cm

30 cm

20 cm

60 cm

5 cm

2 cm0 cm

INDUCTION LOG

LATEROLOG

NEUTRON

GAMMA RAY

DENSITY

SONIC

MICRO RESISTIVITYMICROLOG

DIPMETER

DEPTH OF INVESTIGATION

RESOLUTION

RESISTIVITY

RADIOACTIVITY

RESISTIVITY

ACOUSTIC

Logging Tools

INDUCTION

vs.

LATEROLOG,

When?


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NORMAL MEASUREMENT IN A BOREHOLE

Resistivity in a Homogeneous Medium

!!!

!

"

!!!!

#

$

=

=

==

=

%

I

r

dr

dVR

I

VrR

r

RI

r

drRIV

drr

RIdV

r

2

2

2

4

4

44

4

Current lines

Equipotential

spheres


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LATERAL MEASUREMENT

GUARDED ELECTRODE MEASUREMENT


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16 Short Normal - 1979

1927: 1st wireline resistivity

1st resistivity while drilling

Rapparent = G V/I

Requires conductive, water-

based 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


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DUAL LATEROLOG

LATEROLOG

(GALVANIC)

TOOLS


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LATEROLOG

TOOL CONFIGURATION

ACTUAL TOOL

ELECTRICAL CONDUCTION PHENOMENA

Laterolog Tools


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LATEROLOG TOOL

Different Current Focusing Strategies

LLD CORRECTION CHART

FOR BOREHOLE EFFECTS


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LLDCORRECTION CHART

FOR

INVASION EFFECTS

LLD CORRECTION CHART

FOR BED THICKNESS


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LLS CORRECTION CHART

FOR BED THICKNESS

MICRO

LATEROLOG

DEVICE:

a

Pad Tool


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MSFL TOOL:

aMicro-Laterolog

Device

FORMATION MICRO-IMAGING TOOL


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PHYSICAL

PRINCIPLE OF

INDUCTION

TOOLS

PHYSICAL PRINCIPLE OF INDUCTION TOOLS


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Dual Phasor Array Induction

Multi-Frequency Acquisition

PRINCIPLE OF INDUCTION FOCUSING


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INDUCTION TOOL SENSITIVITY

Ideal Radial

Geometric Factors

Actual RadialGeometric Factors


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FOCUSED SENSITIVITY FUNCTIONS

SKIN EFFECT CORRECTION

(Correction for Frequency-DependentPropagation Effects)


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BOREHOLE CORRECTION

(Correction for Mud Conductivity

And Borehole Size)

BOREHOLE CORRECTION

(Correction for Mud Conductivity And Borehole Size)


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BED THICKNESS CORRECTION

(Induction Log)

INVASION

CORRECTION

(Induction Log)


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SUMMARY

Approximate Interpretation Cycle

EXAMPLE

Skin and Borehole Corrected Induction Curves


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EXAMPLE

Focused Induction Curves

MODERN INTERPRETATION TECHNIQUES


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COMPREHENSIVE

INTERPRETATION PROCESS

(Numerical Simulation andInversion)

EXAMPLE

2-D Inversion Results


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LWD

RESISTIVITY TOOLS

16 Short Normal - 1979 1927: 1st wireline resistivity

1st resistivity while drilling

Rapparent = G V/I

Requires conductive, water-

based drilling fluid

Large borehole effects limit

range Rb < R < 20 Rb

Low quality suitable forcorrelation and resistivity trends

Insulation prone to failure

Obsolete technology


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2 MHz Propagation - 1984

1967 patent by M.Gouilloud

Transverse E-field

Works in conductive orinsulating drilling fluids

Small borehole effects insmooth boreholes

1st quantitative LWDresistivity 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-of-

investigation

Anisotropic formations


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Loop antennas located under slotted metal shields.

Close-Up of Tool

Phase Shift

provides a shallow

resistivity with high

axial resolution

Attenuation

provides a deep

resistivity withlower axial

resolution

DualDepths


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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


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6.75 Toroidal Resistivity

ButtonsToroid

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


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Acknowledgements

Schlumberger

Baker Atlas

Repsol-YPF

Electrical Logging Principles

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