introduction to resistivity logging. outline definitions and uses resistivity in rocks archie’s...

Introduction toResistivity Logging

Introduction toResistivity Logging

OutlineOutline• Definitions and Uses

• Resistivity in Rocks

• Archie’s Equations

• Invasion and Invasion Models

• Measuring Resistivity (Rt and Rxo)• Basic ES Principles• Focused Devices• Micro Resistivity Devices

Resistivity UsesResistivity Uses

• Locate Hydrocarbons

• Identify Water Type

• Correlation

• Identify Lithology of Formations

ResistivityResistivity

• The opposition to flow of electrical current offered by a material of unit length and unit cross sectional area.

V

A

L

r

Measuring ResistivityMeasuring Resistivity

V - Voltage in Volts R - Resistance in Ohms

I - Current in Amperes A - Area in Square Meters

L - Length in Meters

R

V

A

L

R = r L/ A

rV/ I x A/ L

r

k = A/ L

V = R x I

V = rL/ A x I

rV/ I x k

V = I R

V = r L / A I

r = V / I k

R = r L / A

r = V/ I A / L

( k = A / L )

Archie PorosityArchie Porosity

Matrix

Oil

Water

SW = 60%

Eff. = 30%

eff

Water Wet Porosity - RoWater Wet Porosity - Ro

SW = 100%EFF = 30%

Oil And WaterOil And Water

SW = 60%EFF = 30%

Water ResistivityWater Resistivity

RW

Cube filled withSalt Water (Resistivity Rw)

Rt = RwPorosity () = 100%

Rock Matrix ResistivityRock Matrix Resistivity

Rock Cube, Rt = Porosity () = 0%

Hydrocarbon ResistivityHydrocarbon Resistivity

Oil Cube, Rt = Porosity () = 100%

Fresh-Water Filled PorosityFresh-Water Filled Porosity

Archie Cube, Rt =Porosity () = 30%

Salt-Water Filled PorositySalt-Water Filled Porosity

Resistvity 1/

Resistvity RwArchie Cube, Rt > Rw

Porosity () = 30%Rt = Ro

Salt Water & OilSalt Water & Oil

Resistvity 1/SWArchie Cube, Rt >> Rw

Porosity () = 30%

ResistivityResistivity

Which of these “Archie Blocks” has the largest resistivity

Rt = RoRt = Ro Rt > Ro

= 20%Sw = 100%

= 30%Sw = 66%

= 10%Sw = 100%

ResistivityResistivity

Which of these “Archie Blocks” has the largest resistivity

Rt = RoRt = Ro Rt > Ro

= 20%Sw = 100%

= 30%Sw = 66%

= 10%Sw = 100%

> =

True ResistivityTrue Resistivity

Rt =Rwn

Swm

a

ma

- Relates Porosity to Resistivity

m is related to the degree and type of cementation

nSw

- n usually equal to 2

Resistivity FactorsResistivity Factors

• The Formation Resistivity is effected by:

• Volume of Water - (Porosity & Sw)

• Resistivity of Water - (Rw)

• Current path through Water - “m” in Porosity equation

ResistivityResistivity

Which of these “Archie Blocks” has the largest resistivity

Rt = RoRt = Ro Rt > Ro

= 20%Sw = 100%BVW = .02

= 30%Sw = 66%

BVW = .0199

= 10%Sw = 100%BVW = .01

> =

Archie PorosityArchie Porosity

Matrix

Oil

Water

SW = 60%EFF = 30%

EFF

BVW = Sw x = 18%

Idealized Log SetIdealized Log Set

A

B

C

D

E

InvasionInvasion

Mud Filtrate Invasion

Porosity = 30 %

Porosity = 10 %

Porosity = 20 %

mud filtrate

mud filtrate

mud filtrate

mud cake

Zones About the Well-BoreZones About the Well-Bore

Rs

RtRw

Sw

Rxo

Rmf

Sxo

Di

Adjacent Bed

h VirginZone

InvadedZone

tmc - mud cake thickness

Rmc

Adjacent Bed Rm

ShaleShale

No permeability,No Invasion

Res

istiv

ity

Depth of Investigation

Virgin

10 60 90

Low InvasionLow Invasion

Water Zone

Res

istiv

ity

Depth of Investigation

Virgin

10 60 90

Low Invasion - OilLow Invasion - Oil

Low Invasion (Step) - Oil

Res

istiv

ity

Depth of Investigation

10 60 90

Virgin

Transition Zone - OilTransition Zone - OilR

esis

tivity

Depth of Investigation

10 60 90

VirginFlushed

Transition Zone - WaterTransition Zone - WaterR

esis

tivity

Depth of Investigation

10 60 90

VirginFlushed

Transition Zone - OilTransition Zone - Oil

Annulus Profile,Deep Invasion,

Oil

Res

istiv

ity

Depth of Investigation

10 60 90

VirginAnn.Flushed

Basic Log ExampleGR0 150

11000

11100

SFL.2 20

ILM.2 20DPHI 0.50

NPHI.50 0

A

B

C

D

.30

BHT = 230 FTD = 14000 ft.Rmf = 1.41 ohm-m @ 75 F

ILD.2 20S P

A

M

Electrical Survey Measurements

Unfocused SystemUnfocused System

VRa = Ik

EquipotentialSpheres

NormalDevice Lateral

Device

BN

B

Non-focused vs Focused Systems

Dual Laterolog

LLS

Ao Measure Current Electrode

M1 & M2 Monitoring Electrodes

A1 Bucking Current Emitting Electrode

A2 Bucking Current Return Electrode

LLD

Ao Measure Current Electrode

M1 & M2 Monitoring Electrodes

A1 Bucking Current Electrode

A2 Bucking Current Electrode

Spherical Focused Log

Rsfl = k (Vb - Vc)Io

Io Return to Armor

Bucking CurrentMonitoring ElectrodesBuckimg CurrentReturn ElectrodeMonitoring Electrode

Current Electrode

Proximity Log - MicrologAo Mo A1

M2

M1

Ao

AoMoA1M1M2

M2

M1

Ao

MicrologMicrolog