USIT Client Log Features Interpretation

7/27/2019 USIT Client Log Features Interpretation

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USIT Log features

USIT Microdebonding

What to look forin a USIT log

February-2003

Javier Peyrire


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Table of contentsTable of Contents 2

Common formats 3Cement evaluation examples 5

Good Cement 5

Mud Channel 6

Traces of Cement 7

Cement and Squeeze 8

Light Cement 9

Wet Microannulus 10

USIT Image Interpretation and guide 11

Other Effects (examples) 13

Casing shape and wear 14

Third Interface reflection 18

Centralizers 19

To Remember about USIT 20

Microdebonding 21

Background Information 22

Examples 24

Theory and algorithm 28

Examples of microdebonded logs 31

Limitations and advice 35

To remember about Microdebonding 37

Microdebonding References 38

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USI combined casing +cement presentation

QC Casing Cement

Channel

Bond index

Cement raw

Thickness image

ThicknessInternal radius

Cementinterpreted

Casing cross-section

Amplitude

Processing flags

Eccentering, CCL, gamma Ray

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USI + CBL/VDLcement presentation

QC CBL USI VDL

CBL

VDL

Bond indexAcoustic impedance

Cement image interpreted

CBL, Gamma Ray

Process flags, eccentering

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Good cement

Strongformation

arrival

CBLflat,low

MeanAI 8MRayl

Weakcasingarrival

QC CBL USI VDL

The AI value depends on

the type of cement

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Mud channel andcontaminated cement

Weakformation

arrival

CBLvariable,

high Strongcasing arrival

Channel

Low-Zcement

QC CBL USI VDL

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Partial cementation

Weak formationarrival

CBL flat,high Strong casing

arrival

Traces ofcontaminated

cement

QC CBL USI VDL

Patches of cement within

fluid

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Channel and Squeeze

Channel After squeeze

Perfs

USI

CBL

USI BI VDL USI BI VDL

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Light cement top

Low

impedance

0-4 MRayl

scaleshows

contrast

between

light cementand liquid

Liquid/solid

threshold

set low (2.1)

for light

cement

CBL agreeswith USI

0100

0-4MRayl

Threshold2.1 MRayl

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Wet microannulus

USI is weakly affected

CBL reads near free pipe

Strong, regularcasing arrival

High CBL

Uniformmedium-Z

USI

USI BI VDL

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USI image interpretation

High Z

Patchy

Gas

CementLocalised

MediumLiquid

Micro-debonded

Cement Gas entry ifgas zone

Light orcontam. ExtendedCement

NarrowCementdata

Dry micro-Mud

channelMud

layer +cement

annulus(Debond) Gas

channel

No Squeeze ?Squeeze

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USI CBL/VDL

Resolution 0.6 in to 1.2 in. 360 deg. x 3 ft

Well bonded

cement

Cement Cement

Very light

cement

Low contrast

[special processing

if debonded]

Low contrast from

mud

Dry microann.

Debonded

cement

Dry microann. /gas

(special

processing)

Good/fair bond

Wet microann. Slightly affected Ambiguous

Mud layer Channel Ambiguous

Contaminated

cement

Low-Z cement Ambiguous

Mixed lead/tail

cement

Mixed lead/tail Ambiguous

Mud channel Channel Ambiguous

Gas channel Gas channel Cement/ambiguous

Formation bond Not seen VDL qualitative

Outer casing/

hard formation

Third interface

arrival (not

affected)

Strongly affected

Casing

condition

Very sensitive Slightly sensitive

Mud

attenuation

< 12 dB/cm/MHZ No strict limit

USI and CBL/VDL guide

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Other effects

Casing effects

Third arrival effects (formation)

Centralizers effect

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p rad.

Casing shape effects

Manufacturing patterns often

affect cement image slightly

Does not affect interpretationAm Int Cement

Formation

reflections

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Casing wear can affectcement image

Drill pipe wear creates falsechannel

Falsechannel

Weargroove

QC Casing Cement

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Deformed casing

Deformed casing can cause lostechoes and tool eccentering. Even the

eccentering curve becomes false. The

log must be repeated with a wider

Windowacquisition window.Echoesoutside

acquisitionwindow

Max/min TT TT histogram

Eccentering

Lost echoes

QC Casing Cement

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Narrow

side ofannulus

Channel

Third interface reflections

Galaxypattern

Int.radius

CementThickness

Typical galaxy patterns: interference

between casing resonance and reflections

from outer casing (here) or hard formation.

In this example, it shows good cement except

in free pipe when the casing is close to theformation

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Centralizers and goodcement

USI usually seescentralizers

Important to verifyif casing properlycentralized

Casingjoint

Centralizer

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To remember about USIT

USIT-CBL together: gives ananswer for most of the cases

The casing condition will affectthe log

The cement quality is evaluatedreal time

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USITMicro-debonding

Introduction,

description,advice

?

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Background information

USIT gives a value of the Acoustic

Impedance (AI) of the media behindthe casing

In general:

AI gas < 0.3 MRay

AI liquid < 2.6 Mray (water around1.5M ray)

AI conventional cement > 2.6 MRay

AI light cement, foam cement often< 2.6 MRay

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Presentation

Presence of low impedance (gas orliquid range) spots/areas within the

cement

Multiple reasons (mixed with gas,fluid, temperature effects whenhardening, light cement, foamedcement)

Act as a barrier to ultrasound

Patchy cement aspect, low bondetc

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Example 1: patchycement

Patchy gas/cement indicates

micro-debondedcement (patchy drymicro-annulus)

Raw BI Interp

Patches of Gasand Liquid

Patches of Goodcement

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Example 2: Extended dry

microannulus

Debonded Cement

Debonding can be

extensive with lowimpedancevariability and notassociated with

gas entry

Raw BI Interp

Extended debond(reading gas)

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Example 3: Gas Micrannulus

Gas coming tosurface of old

storage well Old CBL showed

almost 100% bondNarrow gas

channelGas microannulus

Good cement

Raw BI Interp

New USI showedareas of debond(gas microannulus)

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Micro-debond on USI andCBL

CBL less affected than USI withoutpressure

USI and CBL

Without pressure

improve with pressure

With pressure

CBL

USI

USI BI VDL USI BI VDL

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Theory or Hypothesis

Gas and liquids have ahomogeneous AI within the same

medium

Solids have a more heterogeneousAI repartition (Variable cementimpedance is indicative of solids)

Cement is a solid (when hardened)

By comparing the AI ofneighbouring points we candetermine if it is a solid or a fluid

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Micro-debonded cementprocessing

VerticalDeviation

Transducer Diagonal 1spot size

Horizontal

Deviation

Diagonal 2

If all 4 standard deviations > setthresholds

Data point is considered to be

locally debonded

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Micro-debond logic

Micro-debonding

algorithmPixel Z AI Thresholds Cement

Liquid

< Thresh

OR

> Thresh

Micro-D

Gas Thresh

Micro-D

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USI micro-debond logic

Classifies patchy low-impedancematerial as micro-debondedcement

Helps interpretation of light andfoam cement LowCBL

FormationarrivalsMicro-debond

presentationConventional

BI CBL VDLBI Map Map

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Micro-debond logicexample

Automatically classifies patchylow-impedance material asmicro-debonded cement

CBL

BI Map CBL VDL

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Debondlogic

Threshold map

BI VDL

LiteCRETE 12 ppg cement

Gas entry from known gas zone

Micro-debond logic showscement is present

CBTBI

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CBTBI

Raw map Z BI Debond

logic

LiteCRETE Gasblok 10.3ppg

Micro-debond logic shows cementis present

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USI micro-debond logiclimitations

Does not work with extended drydebond (gas microannulus)

Empirical threshold

Need to tune thresholdsometimes

Can indicate debonding in achannel due to casing shapeeffects.

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Logging advice

Normal cement

Log with micro-debonding off

Play-back with micro-debondingon if bad bond.

Light/Foam Cement (low AcousticImpedance)

Log with micro-debonding on

Play-back with micro debondingoff to see the AI map (not hiddenby the green micro-debonding

flag)

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To remember

Act as a barrier to ultrasound

Vocabulary: Microdebond is thesame as dry microannulus, gasmicroannulus or dry debond

Indicates solid cement

Often occur without gas entry evenin double casing strings due topressure or temperature changes

Gas entry should only be suspectedif in known gas zone, gas injectorwell near, or gas at surface

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References

Microdebonding: what is it and does it provide hydraulic

isolation?, Andrew Hayman 29 Nov. 2001

SPE 55649, Assessment of FoamedCement Slurries

Using Conventional Cement Evaluation Logs and

Improved Interpretation Methods from Gary J. Frisch,

William L. Graham and James Griffith (SPE, Halliburton)

SPE 19538, Guidelines for Ultrasonic Cement-Sheath

Evaluation from K. J. Goodwin (SPE, Mobil)

Overcoming Interpretation Problems of Gas-

Contaminated Cement Using Ultrasonic Cement Logs

from R.J. Butsch (SPE, Schlumberger)

The Evaluation of Specialized Cements from R.J. Butsch

et al. (SPE, Schlumberger)

USIT Client Log Features Interpretation

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