Chapter 13 Laterologs

Lecture notes for PET 370

Spring 2012

Prepared by: Thomas W. Engler, Ph.D., P.E.

Laterologs

• developed for salt-based muds

• the survey current is focused, thus providing better vertical resolution and deeper depth of investigation.

• minimizes highly resistive adjacent bed effects

• borehole and bed thickness effects are negligible and often ignored.

Introduction

Obsolete

current

LL7, LL3,

guard

DLL-MLL

DLL-

MSFL

1955-80

1972

Deep

Laterolog

(LLD)

Laterolog-7

Laterolog-3 /

Guard

Shallow

Laterolog

(LLS)

Micro-

laterolog

(MLL)

MLL

MSFL

Salt

Mud

Rmf<2Rw

Or

Rt>200

CurrentAIT1990ToolInductionArray

Obsolete

Obsolete

Obsolete

Current

Current

IES, IEL

ISF

DIL-LL8,

DIFL,

DISG

DIL-SFL

Phasor

1955-80

1970-85

1965

1975

1985

Induction

(6FF40)

Deep

Induction

Deep

Phasor

Induction

Medium

Induction

Medium

Phasor

Induction

16”Normal

Spherically

Focused

LL8/Short

Guard

Spherically

Focused

Spherically

Focused

Microlog

(ML)

Minilog

Proximity

(PL)

Fresh

Mud

Rmf>2Rw

Or

Rt<200

obsoleteES, ELup to

1955

18’ Lateral64” Normal16” Normal

CommentsNameYearsDeep

3+ ft

Medium

1.5-3 ft

Shallow

0.5-1.5 ft

Flushed

Zone

1-6 in.

Obsolete

current

LL7, LL3,

guard

DLL-MLL

DLL-

MSFL

1955-80

1972

Deep

Laterolog

(LLD)

Laterolog-7

Laterolog-3 /

Guard

Shallow

Laterolog

(LLS)

Micro-

laterolog

(MLL)

MLL

MSFL

Salt

Mud

Rmf<2Rw

Or

Rt>200

CurrentAIT1990ToolInductionArray

Obsolete

Obsolete

Obsolete

Current

Current

IES, IEL

ISF

DIL-LL8,

DIFL,

DISG

DIL-SFL

Phasor

1955-80

1970-85

1965

1975

1985

Induction

(6FF40)

Deep

Induction

Deep

Phasor

Induction

Medium

Induction

Medium

Phasor

Induction

16”Normal

Spherically

Focused

LL8/Short

Guard

Spherically

Focused

Spherically

Focused

Microlog

(ML)

Minilog

Proximity

(PL)

Fresh

Mud

Rmf>2Rw

Or

Rt<200

obsoleteES, ELup to

1955

18’ Lateral64” Normal16” Normal

CommentsNameYearsDeep

3+ ft

Medium

1.5-3 ft

Shallow

0.5-1.5 ft

Flushed

Zone

1-6 in.

Resistivity Logs Classification

Laterologs

Guard Electrode System

• three electrode system

• focusing current from guard electrodes, A1and A2, maintains zero voltage between Ao and A1 - A2.

• Tradenames: Guard Log, LL3

Types

Laterologs

Point Electrode System

• 7 to 9 electrodes

• focusing current adjusted to maintain zero voltage across the moniter electrodes, M.

• Tradenames: LL7, LL8

Types

Obsolete

current

LL7, LL3,

guard

DLL-MLL

DLL-

MSFL

1955-80

1972

Deep

Laterolog

(LLD)

Laterolog-7

Laterolog-3 /

Guard

Shallow

Laterolog

(LLS)

Micro-

laterolog

(MLL)

MLL

MSFL

Salt

Mud

Rmf<2Rw

Or

Rt>200

CurrentAIT1990ToolInductionArray

Obsolete

Obsolete

Obsolete

Current

Current

IES, IEL

ISF

DIL-LL8,

DIFL,

DISG

DIL-SFL

Phasor

1955-80

1970-85

1965

1975

1985

Induction

(6FF40)

Deep

Induction

Deep

Phasor

Induction

Medium

Induction

Medium

Phasor

Induction

16”Normal

Spherically

Focused

LL8/Short

Guard

Spherically

Focused

Spherically

Focused

Microlog

(ML)

Minilog

Proximity

(PL)

Fresh

Mud

Rmf>2Rw

Or

Rt<200

obsoleteES, ELup to

1955

18’ Lateral64” Normal16” Normal

CommentsNameYearsDeep

3+ ft

Medium

1.5-3 ft

Shallow

0.5-1.5 ft

Flushed

Zone

1-6 in.

Obsolete

current

LL7, LL3,

guard

DLL-MLL

DLL-

MSFL

1955-80

1972

Deep

Laterolog

(LLD)

Laterolog-7

Laterolog-3 /

Guard

Shallow

Laterolog

(LLS)

Micro-

laterolog

(MLL)

MLL

MSFL

Salt

Mud

Rmf<2Rw

Or

Rt>200

CurrentAIT1990ToolInductionArray

Obsolete

Obsolete

Obsolete

Current

Current

IES, IEL

ISF

DIL-LL8,

DIFL,

DISG

DIL-SFL

Phasor

1955-80

1970-85

1965

1975

1985

Induction

(6FF40)

Deep

Induction

Deep

Phasor

Induction

Medium

Induction

Medium

Phasor

Induction

16”Normal

Spherically

Focused

LL8/Short

Guard

Spherically

Focused

Spherically

Focused

Microlog

(ML)

Minilog

Proximity

(PL)

Fresh

Mud

Rmf>2Rw

Or

Rt<200

obsoleteES, ELup to

1955

18’ Lateral64” Normal16” Normal

CommentsNameYearsDeep

3+ ft

Medium

1.5-3 ft

Shallow

0.5-1.5 ft

Flushed

Zone

1-6 in.

Resistivity Logs Classification

Laterologs Types

Current flow path for LLD and LLS

Schematic diagram of the DLL-Rxo tool

Dual laterolog (LLS/LLD) - obtained by

using currents at different frequencies.

shallow and deep curves

Laterologs Theory

n

1=i

1i

J where

sR

sJR

tJ

iR

iJ

xoR

xoJ

mcR

mcJ

mR

mJ

aR

J is the integrated pseudogeometric factor

J = f(tool type, di)

Laterologs

Integrated geometrical factor 50% of signal contribution from a depth of:

8” MSFL

25” LLS

>80” LLD

Theory

Laterologs

• Numerous factors influence the apparent resistivity measurement: – borehole effects (Rm, Rmc, dH, hmc) – adjacent beds (h, Rs) – invaded zone (di, Ri, Rxo) – uninvaded zone (Rt)

• Charts have been developed using math simulations to correct for these

effects. Corrections are sequenced!

Borehole

Adjacent bed

Invasion

True formation resistivity

Application

Laterologs

Assume a step profile of invasion

Analytical solution

- three unknowns: di, Rxo, Rt

Invasion

d

R

Assumed di

Rxo LLd

Rt

LLs msfl

tR*))id(''xoJ1(xoR)id(''xoJMSFL)''aR(

tR*))id('xoJ1(xoR)id('xoJ LLS)''aR(

tR*))id(xoJ1(xoR)id(xoJ LLD)''aR(

Laterologs

Invasion

Tornado Chart for Dual-Laterolog-Rxo Device

(Schlumberger)

Laterologs Example

Laterologs

Example

Bassiouni, Z: Theory, Measurement, and Interpretation of Well Logs, SPE Textbook Series, Vol. 4, (1994)

Chapter 5

Schlumberger, Log Interpretation Charts, Houston, TX (1995)

Western Atlas, Log Interpretation Charts, Houston, TX (1992)

Resistivity Logs References