Resistivity Logging Tools COPYRIGHTcloud1.activelearner.com/contentcloud/portals/... · spacings Lateral Logs ... Used for LWD and open hole coring and analysis Generally less accurate

Open Hole Well Logging Refresher

Resistivity Logging Tools and Interpretation Core

Learning Objectives

By the end of this lesson, you will be able to:

Discuss wireline logging concepts and describe surface andsubsurface systems

Explain how depths are determined during logging

Discuss the difference between driller’s depth and logger’sdepth

Explain the differences between MD, TVD, and TVDSS andwhen each is needed

Describe the early resistivity log—the Lateral Log


©PetroSkills, LLC. All Rights Reserved. _________________________________________________________________________________________________________

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Wireline Logging (Refresher)

Logging Tool

The Birth of Resistivity Logging



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The First Resistivity Logging Tool

Distinguishing characteristic:AM = longMN = short

Radius of investigation

18’ 8” (5.5 m)Long AO spacing Invaded zone resistivity has less influence on deep investigation spacing



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The Evolution of Resistivity Logging Tools

Lateral Log

Late 1920s–1930s

The Cold War

West

Soviet Union

technology

Induction Log, Laterolog

Lateral Log, multiple electrode spacings Lateral Logs

1990

World War II

Late 1930s–Late 1940s

Logging slowed

Lateral Log, multiple spacings Lateral Logs

Russian Well Log Evaluation

Modern Resistivity Logging Units

Onshore Wireline Unit Offshore Wireline Unit

Courtesy of Schlumberger Courtesy of Baker Hughes



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Courtesy of Halliburton

Computers

Wireline Winch

Depth: What Is Proper?

Depth



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Logger’s Depth (LD) Wireline measurement

utilizing a calibrated cable and wheel

All log analysis is carried out using the loggers’ depth

Also Measured Depth (MD)

Generally most accurate

Driller’s Depth (DD) Determined by adding drill

pipe stands

Used for LWD and open hole coring and analysis

Generally less accurate than LD

A correction is generally required from DD to LD because:

DD is not stretch-corrected and LD is.

Logger’s Depth

Most accurate—Calibrated measurement wheel and magnetic marks on the cable

Corrected for stretch

Not perfect—May not be lowered to the very bottom of the borehole

Casing shoe

TD: Depth logger ≤ Depth driller



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The Logging System

The Logging System – Wireline Cable

Wireline Fishing(a bad trip!)

Electrical Wireline Cable Head

Electrical & mechanical connection

Weak point



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Safe Operations

Safe Operations

Equipment Hard hats

Hearing protection

Safety glasses

Gloves

Fire-retardant coveralls

Steel-toed boots



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Safe Operations

At the Wellsite Hazards—radioactivity, explosives, pressure

Job Hazard Analysis (JHA)• Hot work permits• Cold work permits• Material Safety Data Sheet (MSDS)

Logging Depth Control

First Survey in Well Usually GR/SP-Resistivity

log Calibration using magnetic

marks

Subsequent Surveys (Same Section) Correlated to first survey Errors due to tool weight

diff., traveling block movements

Subsequent Surveys (New Section) First log must include GR Overlap of >50m (~165’) with

previous GR

1st Survey

Casing shoe: Depth logger = Depth driller ±0.1%

Subsequent Survey(same section)

Subsequent Survey(new section)



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Stretch corrections to WL

Vertical Well MD = TVD

Deviated Well MD ≠ TVD

TVD converts to TVDSS for geologist and reservoir engineer


Measured Depth

Used for well operations

Required to• Run casing and tubing• Perforate casing• Set packers and plugs• Other downhole

activity

True Vertical Depth

Used for • Geologic mapping • Reservoir engineering

Required to determine• Pressure• Temperature• Fluid properties



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Newer Generation of Compact Logging Tools

Standard Triple Combo90 feet (27.4 m)

Platform Express38 feet (1.6 m)


Triple Combo1. Resistivity

2. Density

3. Neutron porosity

SP

GR

Micro-Resistivity

Resistivity

Density

Neutron porosity

Gamma Ray

Micro-resistivity



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Triple Combo Quad Combo


Platform Express Specifications

38 ft (11.5 m) length

690 lbm (313 kg)

3⅜-in. (8.6 cm) minimum OD

4⅝-in. (11.75 cm) maximum OD

260° F (127° C)

10,000 psi (68,950 kPa)

6- to 16-in. (15-40 cm) hole sizes

3600 ft/hr (1100 m/hr)



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Learning Objectives


Discuss wireline logging concepts and describe surface and subsurface systems


Discuss the difference between driller’s depth and logger’s depth

Explain the differences between MD, TVD, and TVDSS and when each is needed


You are now able to:



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What Is Resistivity and Why Is It Important?

Learning Objectives


Explain what resistivity is and why is it important to well logging and formation evaluation

State why resistivity is a key parameter for hydrocarbon evaluation

Define resistivity and explain the units used for measuring it

Explain relationship between conductivity and resistivity

State the resistivities of several subsurface formations and fluids



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Resistivity Defined

Resistivity:• a fundamental material property that represents how strongly a

material opposes the flow of electric current• the electrical resistance per meter of length and per square

meter of cross-sectional area (a cube one meter long and one meter square)

Measured in ohm-meter2/meter or ohm-meter (Ω.m).

R = 1 ohm.m (or Ω.m) if a 1 m cube has 1 Ω of resistance

Shaly sandstones0.5–50 Ω.m

Carbonates100–1,000 Ω.m

Evaporites1,000s Ω.m

Resistivity Defined

Typical Formation Resistivities

0.5 Ω.m 1,000 Ω.m



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Resistivity Defined

Typical Formation Resistivities

0.5 Ω.m 1,000 Ω.m

Shaly sandstones0.5–50 Ω.m

Carbonates100–1,000 Ω.m

Evaporites1,000s Ω.m

Formation waters(brine – fresh)0.01–10 Ω.m

Sea water @ 75ºF~0.35 Ω.m

Resistivity Defined

Conductivity is the inverse of resistivity.

Units

mhos/m or millimhos/m

In the 1970s,siemens replaced mhos

C = 1R

1 Ω.m = 1,000 millisiemens/m

1,000 Ω.m = 1 millisiemens



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The Importance of Resistivity

Electrical resistivity is the most sensitive parameter to distinguish between salt water and hydrocarbons.




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Water saturation = 100%No hydrocarbons

Water saturation < 100%Likely hydrocarbons



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Key Concepts to Remember About Resistivity

Electrical resistivity is

a sensitive parameter

to distinguish

between salt water

and hydrocarbons.

Salt water fair conductor, low resistivity

Oil and gasinsulators, high resistivity

Fresh waterintermediate based on salinity

Challenges When Measuring Resistivity

Borehole effects

Fluid in the borehole

Effects of neighboring beds or layers

Effects of mud filtrate invasion



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Learning Objectives


Explain what resistivity is and why is it important to well logging and formation evaluation

State why resistivity is a key parameter for hydrocarbon evaluation

Define resistivity and explain the units used for measuring it

Explain relationship between conductivity and resistivity

State the resistivities of several subsurface formations and fluids

You now can:



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Resistivity Logging and Interpretation Core

Invasion and the Borehole EnvironmentPart 1

Learning Objectives


Explain mud filtrate invasion and describe the borehole environment in terms of resistivity

State the resistivities in each zone within the borehole environment

Discuss the distribution of fluids in a hydrocarbon reservoir

List three or more types of drilling muds and identify whether their respective filtrates are low or high resistivity

Explain the effect of temperature on resistivity of a NaCl saltwater solution



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Saturation Profile: Hydrocarbon-Bearing Rock

Saturation Profile: Hydrocarbon-Bearing Rock



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Saturation Profile: Invaded Rock




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Drill DrillTrip

1 10 100 1000 10,000 100,000

Depth of Invasion

Mud Cake Thickness

Rate of Invasion

Minutes after Penetration

Invasion Effects

After Dewan, 1983, Fig. 1-5, p. 11



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Drill DrillTrip

1 10 100 1000 10,000 100,000

Depth of Invasion

Mud Cake Thickness

Rate of Invasion


Invasion Effects


Invasion DepthTypical: 1–2 ft. (0.3–0.6 m)Range: 0.1–10 ft (0.03–3 m)

Invasion Effects

Depth of Invasion increases quickly in the first few minutes.

Rate of Invasion starts fast; slows once mud cake forms.

Mud Cake Thickness grows steadily; knocked off when drillpipe is tripped in.

Drill DrillTrip

1 10 100 1000 10,000 100,000

Depth of Invasion

Mud Cake Thickness

Rate of Invasion





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The Borehole Environment




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Flushed zone


Flushed zone



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Flushed zone


Flushed zone



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Zone of transition or annulus


Uninvaded zone



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Uninvaded zone

(Bed Thickness)


Uninvaded zone

(Bed Thickness)



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Uninvaded zone

(Bed Thickness)




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Learning Objectives







You now can:



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Invasion and the Borehole Environment

Part 2

Zones In and Around the Borehole

Zone DimensionFluid

ContentFluid

ResistivityRock

ResistivityWater

Saturation

Bed h Rt

Adjacent Bed

Rs

Borehole dhMud Rm

Mud Cake hmc

Flushed di Mud Filtrate Rmf Rxo Sxo

UninvadedConnate Water

Rw Rt, Ro Sw



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Zone DimensionFluid

ContentFluid

ResistivityRock

ResistivityWater

Saturation

Bed h Rt

Adjacent Bed

Rs

Borehole dhMud Rm

Mud Cake hmc



Rw Rt, Ro Sw


Zone DimensionFluid

ContentFluid

ResistivityRock

ResistivityWater

Saturation

Bed h Rt

Adjacent Bed

Rs

Borehole dhMud Rm

Mud Cake hmc



Rw Rt, Ro Sw



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Zone DimensionFluid

ContentFluid

ResistivityRock

ResistivityWater

Saturation

Bed h Rt

Adjacent Bed

Rs

Borehole dhMud Rm

Mud Cake hmc



Rw Rt, Ro Sw


Zone DimensionFluid

ContentFluid

ResistivityRock

ResistivityWater

Saturation

Bed h Rt

Adjacent Bed

Rs

Borehole dhMud Rm

Mud Cake hmc



Rw Rt, Ro Sw



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Zone DimensionFluid

ContentFluid

ResistivityRock

ResistivityWater

Saturation

Bed h Rt

Adjacent Bed

Rs

Borehole dhMud Rm

Mud Cake hmc



Rw Rt, Ro Sw


Zone DimensionFluid

ContentFluid

ResistivityRock

ResistivityWater

Saturation

Bed h Rt

Adjacent Bed

Rs

Borehole dhMud Rm

Mud Cake hmc



Rw Rt, Ro Sw



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Invasion of Borehole Wall

Borehole wall

Minimize mud filtrate invasion




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Mud Cake Quality

Properties of the mud

Amount of overbalance (pressure)

Time

Filtrate Invasion

Properties of the mud(API Fluid Loss)

Time

Porosity and permeability

API Fluid Loss• The amount of fluid (in cc)

through a standard milliporefilter with 100 lbs differential pressure in 30 mins

• ≤ 10 cc for water-based muds• ≤ 4 cc for oil-based muds


Tools affected:

• Resistivity

• Density: porosity calculation requires mud filtrate

density

• Sonic: can be corrected using Gassmann equation



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Invasion and the Borehole Environment

Part 3

Mud Filtrate Invasion

porosity (ϕ) = diameter of intrusion (di)



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Mud Filtrate Invasion

porosity (ϕ) = diameter of intrusion (di)

Basic Types of Drilling Mud

The Mud Circulating System



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The Mud Circulating System


Water-Based Mud (WBM)

Saltwater Mud

Oil-Based Mud (OBM) Synthetic Oil-Based Mud (SOBM)

Water-Based Mud (WBM)

Least expensive

Fresh, brackish, or sea water

Type of water affects Rmf

Saltwater Mud More efficient in some

formations

NaCl or KCl

Oil-Based Mud (OBM) More lubricating

Made with diesel or crude oil

Rarely used for environmental reasons, expense of disposal

Synthetic Oil-Based Mud (SOBM)

Expensive

Used in deep-water drilling

Uses food-quality mineral oil



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Properties of Muds

Water-based muds (WBM and saltwater)

• Have water filtrate

• Rw measured and recorded

Oil-based muds (OBM and SOBM)

• Oil filtrate is not conductive

• Rm, Rmc, and Rmf are not meaningful

• Resistivity logging tools with electrodes will not function in OBM

Wellsite Measurement of Rmf



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Resistivity of NaCI Solutions

Resistivity of NaCI Solutions

“9 pound salt water”1.08 gm/cc NaCl



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Conversion to Resistivity

R1

T1T1ppm TDST2

235

R2

R2 = Rmf = 0.024 ohm.m at depth

0.024


Arps Equation R2 = R1[(T1 + 6.77)/(T2 + 6.77)] oF

R2 = R1 [(T1 + 21.5)/(T2 + 21.5)] oC



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R2 = R1 [(T1 + 21.5)/(T2 + 21.5)] oC



R2 = R1 [(T1 + 21.5)/(T2 + 21.5)] oC



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R2 = R1 [(T1 + 21.5)/(T2 + 21.5)] oC

Alphabet Soup—Resistivities

Water-Based Mud and Formation Fluid

Rm Resistivity of the drilling mud (qualitative indicator of mud type)

Rmf Resistivity of the drilling mud filtrate (key parameter)

Rmc Resistivity of the drilling mud cake (seldom needed)

Rw Resistivity of the formation water (key parameter)

Formation

Rxo Resistivity of area flushed by mud filtrate (Flushed Zone)

Rt Resistivity of the uninvaded formation (no saturating fluid)

Ro Resistivity of the uninvaded formation with 100% water

saturation



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Alphabet Soup—Saturations

Sxo Water saturation in the Flushed Zone (often mud filtrate

saturation)

Sw Water saturation in the Uninvaded Zone

Swi Initial water saturation

Swirr Irreducible water saturation

So Oil saturation in Uninvaded Zone (So = 1 – Sw if no gas is

present)

Sg Gas saturation in Uninvaded Zone (Sg = 1 – Sw in a gas

reservoir)

ROS Remaining oil saturation

Sor Residual oil saturation after water-flood

Alphabet Soup—Archie Relationships

Archie I F = Ro/Rw = formation factor

Archie II F = 1/Φm = formation factor in terms of porosity

• Φ = porosity

• m = cementation exponent

I = R

Archie III Rt/Ro = resistivity index

Sw = (1/I) (1/n) = water saturation in terms of resistivity index

• n = saturation exponent

Sw = [(Rw)/(fm x Rt)]1/n = water saturation (resistivity & porosity)



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Factors Affecting Resistivity Tools

MudRm

Formation Resistivity Measuring DeviceShoulder bed

Rs Shoulder bedRs

Shoulder bedRs

Shoulder bedRs

Flushed (Invaded)

ZoneRxo

Flushed (Invaded)

ZoneRxo

Undisturbed Zone

Rt

Undisturbed Zone

Rt

Goal of Resistivity Logging Goal of Resistivity Logging

Learning Objectives







You should now be able to:



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Resistivity Logging Toolsand Interpretation Core

The Resistivity Logging Tools

Learning Objectives


Explain the tool physics and applications of resistivity logging tools

Discuss the relationship between a logging tool’s depth of investigation and bed resolution

Describe the ideal mud properties and formation environment for good Induction log and Laterolog log data

Explain the purpose of the “tornado charts”

Compare and contrast the wireline Induction log and the LWD EWR log

Discuss the types of microresistivity logs



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Sources of Resistivity Measurements

Old electric logs (lateral log, normal log)

Induction logs

Laterologs

Microresistivity logs

Dielectic logs (microwaves)

LWD EWR and resistivity at the bit

Laterolog ≠ Lateral log



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Open Hole Well Logging Refresher

Learning Objectives









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Wireline Logging (Refresher)

Logging Tool




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The First Resistivity Logging Tool

Distinguishing characteristic:AM = longMN = short

Radius of investigation

18’ 8” (5.5 m)Long AO spacing Invaded zone resistivity has less influence on deep investigation spacing



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The Evolution of Resistivity Logging Tools

Lateral Log

Late 1920s–1930s

The Cold War

West

Soviet Union

technology

Induction Log, Laterolog

Lateral Log, multiple electrode spacings Lateral Logs

1990

World War II

Late 1930s–Late 1940s

Logging slowed

Lateral Log, multiple spacings Lateral Logs

Russian Well Log Evaluation


Onshore Wireline Unit Offshore Wireline Unit

Courtesy of Schlumberger Courtesy of Baker Hughes



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Courtesy of Halliburton

Computers

Wireline Winch


Depth



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Logger’s Depth (LD) Wireline measurement

utilizing a calibrated cable and wheel

All log analysis is carried out using the loggers’ depth

Also Measured Depth (MD)

Generally most accurate

Driller’s Depth (DD) Determined by adding drill

pipe stands

Used for LWD and open hole coring and analysis

Generally less accurate than LD

A correction is generally required from DD to LD because:

DD is not stretch-corrected and LD is.

Logger’s Depth

Corrected for stretch

Not perfect—May not be lowered to the very bottom of the borehole

Most accurate—Calibrated measurement wheel and magnetic marks on the cable

Casing shoe

TD: Depth logger ≤ Depth driller



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The Logging System

The Logging System – Wireline Cable

Wireline Fishing(a bad trip!)

Electrical Wireline Cable Head

Electrical & mechanical connection

Weak point



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Safe Operations

Safe Operations

Equipment Hard hats

Hearing protection

Safety glasses

Gloves

Fire-retardant coveralls

Steel-toed boots



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Safe Operations

At the Wellsite Hazards—radioactivity, explosives, pressure

Job Hazard Analysis (JHA)• Hot work permits• Cold work permits• Material Safety Data Sheet (MSDS)


First Survey in Well Usually GR/SP-Resistivity log Calibration using magnetic

marks

Subsequent Surveys (Same Section) Correlated to first survey Errors due to tool weight diff.,

traveling block movements

Subsequent Surveys (New Section) First log must include GR Overlap of >50m (~165’) with

previous GR

1st Survey

Casing shoe: Depth logger = Depth driller ±0.1%

Subsequent Survey(same section)

Subsequent Survey(new section)



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Stretch corrections to WL

Vertical Well MD = TVD

Deviated Well MD ≠ TVD

TVD converts to TVDSS for geologist and reservoir engineer


Measured Depth

Used for well operations

Required to• Run casing and tubing• Perforate casing• Set packers and plugs• Other downhole

activity

True Vertical Depth

Used for • Geologic mapping • Reservoir engineering

Required to determine• Pressure• Temperature• Fluid properties



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Standard Triple Combo90 feet (27.4 m)

Platform Express38 feet (1.6 m)


Triple Combo1. Resistivity

2. Density

3. Neutron porosity

SP

GR

Microlog

Resistivity

Density

Neutron porosity

Gamma Ray

Micro-resistivity



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Triple Combo Quad Combo


Platform Express Specifications

38 ft (11.5 m) length

690 lbm (313 kg)

3⅜-in. (8.6 cm) minimum OD

4⅝-in. (11.75 cm) maximum OD

260° F (127° C)

10,000 psi (68,950 kPa)

6- to 16-in. (15-40 cm) hole sizes

3600 ft/hr (1100 m/hr)



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Learning Objectives







You are now able to:



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The Resistivity Logging Tools –

Induction Logs

Depth of Investigation and Resolution

frequency =

frequency =

Induction Log and Laterolog

depth of investigation

depth of investigation



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Depth of Investigation and Resolution

Deeper depth of investigation

Worse resolution

Shallower depth of investigation

Better resolution

Induction Logs

Step up from “electric logs”

Measure conductivity—the inverse of resistivity

• Units: mhos/m, millimhos/m, or millisiemens

Apparent conductivity (Ca)

• Ca = Cmud + Cxo + Ct

•

High-resistivity muds provide best resistivity data

Conductive, saltwater muds provide poor resistivity data

Ca

Rm Rxo



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Induction Logs

Pros More focused than old

electric logs

Measure multiple depths (ILM, ILD)

Work well in freshwater muds, air-filled wells, and oil-based muds

Cons Poor bed resolution

(~ 6 ft or 1.8 m)

Poor performance in salt mud systems

Newer AIT devices provide better data than DIL

• Calculate numerous measurement diameters

• Higher tolerance for saline boreholes

• Calculate several thin bed resolutions

Induction Logs

6FF40 Introduced in 1950s

6 induction coils, 40” (1 m) spacing

1 deep-reading conductivity curve

Short normal log for shallow resistivity curve

Primary resistivity log for freshwater mud wells



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Induction Logs

Dual Induction Log (DIL) Introduced in 1960s, still run today

2 measurement diameters• Medium depth (ILM)• Deep reading (ILD)

Included LL8 (later SFL, MSFL) for shallow resistivity curve

Multiple readings to correct Ra to Rt

Induction Logs

Induction logs work best in:

Low resistivity formations

Low Rt and high Rxo

A low resistivity zone between high resistivity shoulder beds

Oil-based mud (OBM & SOBM)

MudHIGHRm

Shoulder bedHIGH Rs

Shoulder bedHIGH Rs

Flushed (Invaded)

ZoneHIGH Rxo

Undisturbed Zone

LOW/MOD Rt



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Induction Logs

Example:

SOBM has a resistivity of 2000 Ω.m (conductivity = 0.5 mS/m)

Conductivity = 1/resistivity, so divide 2000 Ω.m into 1 S/m, or 1000 mS/m. Therefore, 1000/2000 Ω.m = 0.5 mS/m)

Rt is 20 Ω.m (conductivity = 50 mS/m)

Divide 20 Ω.m into 1 S/m, or 1000 mS/m. Therefore, 1000/20 Ω.m = 50 mS/m)

The mud in this borehole with 0.5 mS/m has a very small influence on the deep formation conductivity of 50 mS/m.

Dual Induction Logs

ILD

ILM

SFL



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Dual Induction Logs

ILD

ILM

SFL

Conclusions

WBM(have SP and MSFL curves)

Relatively fresh water mud(large separation between SFL and ILD curves)

Interval is water-bearing(low resistivity of ILD curve)

Bottom interval is impermeable(all curves similar)

Dual Induction Logs

ILD

ILM

SFL



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Newer Induction Tools

Phasor Processing of 6FF40

Improve processing of 6FF40

3 frequencies and complex sharpening filter improve thin bed resolution and resistivities



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Array Induction Tool (AIT)

Multiple transmitter-receiver sets

28 signals

5 depths of investigation

3-D Explorer

Introduced commercially in early 2000s

Acquires horizontal and vertical resistivities

3 orthogonal measurements—X, Y, and Z

2 oriented conductivities—horizontal and vertical



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Rt Scanner

Combination of AIT and 3DX

Rt Scanner tool downhole logging

Formation image created by Rt

Scanner

Induction Logs—Summary

Emit electromagnetic waves

Measure conductivity

Ideal for Rt in low resistivity zones

Work in freshwater and oil-based mud and air-filled holes



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Newer Induction Logs—Summary

Tool Comparison

AIT provide better thin bed resolution and more accurate Rtthan DIL.

3DX and Rt Scanner cost more than AIT or DIL; only justified for highly laminated thin beds.



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Laterologs

Laterologs

Step up from “electric logs”

WBM required for operation

Use current beams to focus

Multiple measurements diameters (LLS and LLD or an array of multiple depths of investigation)

Measure apparent resistivity: Ra = RMud + Rxo + Rt



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Laterologs

Pros

Improved bed resolution

Work best in salt muds and within high resistivity formations

Cons

Poor in fresh mud

Poor in low resistivity formations

Not a good choice where Rxo > Rt

All ideal conditions for Induction Logs

Laterologs



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Laterologs

Central emitting electrode

Laterologs

Control current electrode

Control current electrode



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Laterologs

With bucking electrodes Without bucking electrodes

Laterologs



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Dual Laterologs

Dual Laterologs



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Laterologs

Laterologs work best in:

High resistivity formations

Low Rxo

Low resistivity shoulder beds

Saltwater muds (low resistivity)

MudLOWRm

Shoulder bedLOW Rs

Shoulder bedLOW Rs

Flushed (Invaded)

ZoneLOW Rxo

Undisturbed Zone

HIGH Rt



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Microresistivity Logs


MudRm

Shoulder bedRs

Shoulder bedRs

Shoulder bedRs

Shoulder bedRs

Flushed (Invaded)

ZoneRxo

Flushed (Invaded)

ZoneRxo

Undisturbed Zone

Rt

Undisturbed Zone

Rt

Goal of Resistivity Logging Goal of Resistivity Logging



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Designed to measure flushed zone resistivity (Rxo)

MudRm

Shoulder bedRs

Shoulder bedRs

Shoulder bedRs

Shoulder bedRs

Flushed (Invaded)

ZoneRxo

Flushed (Invaded)

ZoneRxo

Undisturbed Zone

Rt

Undisturbed Zone

Rt

Goal of Microresistivity Logging


Pros

Very good vertical resolution

Depth of investigation very shallow (to read flushed zone)

Cons

Depth of investigation very shallow (subject to borehole effects)

Can be adversely affected by condition of mud and rugosity of borehole



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Two Types of Microresistivity Devices

Mandrel Devices (no contact with formation)

Pad Devices(direct contact with formation)

16" Short normal (SN) –old electric

Laterolog 8 (LL8)

Spherically Focused Log (SFL)

AIT calculated shallow curves

Microlog (ML)

Microlaterolog (MLL)

Micro Spherically Focused Log (MSFL)

Micro Cylindrically Focused Log (MCFL)

Inexpensive shallow data, but not always a good Rxoreading.

MSFL and MCFL are the most modern and provide good Rxo data.

Pad Devices—The Microlog

Oil-filled rubber pad pressed against hole wall

Measuring electrodes provide excellent thin bed detection



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Pad Devices—The Microlog

Pad Devices—Microlaterolog

Similar to Microlog, but with 4 concentric electrodes

Mud cake as little influence up to ⅜” (1 cm) mud cake thickness

Uninvaded formation does not affect response if invasion depth is > 3–4” (7–10 cm)

Largely replaced by MSFL



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Pad Devices—MSFL and MCFL

Micro Spherically Focused Log (MSFL) Similar to Microlaterolog

Different electrode spacing and distribution to reduce effect of mud cake

Main signal contribution from 1–2” (2.5–5 cm) behind mud cake

Micro Cylindrically Focused Log (MCFL) Newer version of MSFL

Both are good for measuring Rxo.


No longer run extensively

Largely replaced by AIT and Array Laterolog

Still run where Rxo data are needed



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Comparing Tools

Measuring Resistivity

Dual Laterolog Tool (DLT) Designed for conductive

drilling muds

Shallow and deep depths of investigation

Provides shallow (LLS) and deep (LLD) resistivity measurement

Does not function in non-conductive mud environments



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The AIT and Array Laterolog

Provide 5+ depths of investigation

Largely replaced dual resistivity tools

Dual Induction Tool (DIT) Works best in non-conductive

drilling mud.

Strength of induced current related to conductivity of the formation

2 depths of investigation

Provides induction medium (LM) and induction deep (LD) resistivitycurves


Saline Muds Dual Laterolog (DLL)

• Laterolog deep (LLD)• Laterolog shallow (LLS)

Micro Spherically Focused Log (MSFL)

Freshwater and Oil-Based Muds

Dual induction Log (DIL)• Induction log deep (ILD)• Induction log medium (ILM)



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“Typical” Resistivity Log Presentation

Laterolog Readings over anOil- and Water-Bearing Sand

(Ω.m)0.220

GR (API cts)

LL deep

LL shallow

MSFL

Logarithmic scale (0.2–20 Ω.m)



Multiple curves

Multiple investigation diameters

Qualitative interpretations• Porosity

• Fluid contacts

• Permeability

(Ω.m)0.220

GR (API cts)



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(Ω.m)0.220

GR (API cts)

Porous wet zone

Saltwater mud with same salinity as formation water



(Ω.m)0.220

GR (API cts)

Hydrocarbon-water contact (OWC) or oil/gas column above



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Unable to distinguish oil from gas

(Ω.m)0.220

GR (API cts)



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LWD EWR

Logging While Drilling (LWD) Resistivity

How to choose: Wireline or LWD?



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Example 1: Offshore deepwater well with short drilling times

Wireline• High rig rates ($300k/day)

LWD• Triple combo tool set ($30k/day)• Dipole sonic ($10k/day)


Example 2: Land well with long drilling times

Wireline• Low rig rates• Pay logging company $100k to $1m to run logs

LWD• Per day rate adds up over time



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LWD Tools

Resistivity at the bit (RAB)

Laterolog

EWR

LWD Tools

Wireline measurement principles adapted for LWD

EWR have multiple depths of investigation similar to wireline

RAB can read at or close to bit

EWR and Laterolog can measure formation resistivity prior to invasion

Horizontal wells drilled with OBM: run the EWR tool

Can be run after drilling to study invasion and resistivity over time



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LWD Tools—The EWR Tool

Same EM principle as Induction log

Higher frequency (2 mHz)

LWD Resistivity: The EWR Tool

2 transmitters

2 receivers

2 resistivity curves• Phase shift resistivity• Attenuation resistivity

Latest tools more sophisticated but similar in function



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LWD Resistivity: The EWR Tool

Similar to DIT and AIT

Responds to conductivity

Water- and oil-based muds

Multiple depths of investigation

Bed resolution to 1 foot (0.3 m)



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The Quest for Rt

Learning Objectives


Explain the borehole environment architecture that can cause Rtdetermination to be difficult

Describe the limitations of the conventional induction log and Laterolog and discuss why the modern array resistivity tools provide better data

Explain what is different about the 3DX induction tool and how it can provide better resistivity in anisotropic formations

Identify the process and advantages of the inversion and modeling approach to Rt determination



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The Anisotrophic Environment

Isotropic Anisotropic

Factors within the Anisotrophic Environment

Borehole diameter

Bed 1

Bed 2

Bed 3

Tool

Mud salinity

Mud filtrate

invasion

Formation layering (bed thicknesses)



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Limitations of Standard Tools

Induction Log Response in a Highly Deviated Well

Standard deep-induction curve

Spherically focused log (SFL)

Overcoming Limitations of Standard Tools

ProblemStandard tools are not suitable for:

Thinly layered reservoirs

Deep invasion

Highly deviated and horizontal wells

Anisotropic laminated reservoirs

Solutions Array induction and array

Laterolog tools

3dx (or tilt) induction tools

Inversion processing



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Reconciliation of Rt in Laminated Sequences

Log Response of Oil-Producing Thin Beds

6585

Production test: 1750 bbl/d

New Tools

High-Resolution Laterolog Array (HRLA)

HRLA

DLLGR



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New Tools

Tilt Tool or 3-D Explorer (3dx)

New Tools




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New Tools


New Tools


Mainly Isotropic Thick beds Good reservoir

quality



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New Tools



quality

Mainly Anisotropic Laminated

sand/shales Good reservoir

quality

New Tools



quality

Mainly Anisotropic Laminated

sand/shales Good reservoir

quality

HDILresistivity



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New Tools


New Tools


True resistivity



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New Tools


True resistivity

HDILresistivity

New Tools


Vertical resistivity

Horizontal resistivity



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New Tools


Horizontalsaturation

Hydrocarbon saturation

Capillary pressure

New Tools




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New Tools—3-D Explorer

3DX

Tilt / 3-D Explorer

Shale (low Rt)

Sand (high Rt)

Conventional

Reconciliation of Rt in Laminated Sequences

Laterolog Response in Laminated Shaly Sands

Shale resistivity

~1 Ω-m

Sand resistivity~10 Ω-m

Laterolog response~4 Ω-m



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Inversion and Modeling


Field Log Model-Generated Log



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Modeling of the Laterolog Resistivity Tool Response

Laterolog deep curve

Rt curve resulting from inversion and modeling


1-D Model 2-D Model 3-D Model

Formation layersBed dipBorehole deviation

Formation layersBed dipBorehole deviationInvasion

Formation layersBed dipBorehole deviationInvasion



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Inversion of ILD Compared with Halliburton’s High-Resolution Induction HDRS

Conventional ILD

Halliburton high-resolution induction

Inversion and modeling

Does it really matter?

The Quest for Rt



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The Quest for Rt

Modeling and inversion resulted in

8% higher yields!

North Sea Reservoir (44 degree dip)

Learning Objectives


Explain the borehole environment architecture that can cause Rtdetermination to be difficult

Describe the limitations of the conventional induction log and Laterolog and discuss why the modern array resistivity tools provide better data

Explain what is different about the 3DX induction tool and how it can provide better resistivity in anisotropic formations

Identify the process and advantages of the inversion and modeling approach to Rt determination

You now can:



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Documents

Resistivity Logging Tools COPYRIGHTcloud1.activelearner.com/contentcloud/portals/... · spacings Lateral Logs ... Used for LWD and open hole coring and analysis Generally less accurate