Kuliah-2 Cement Evaluation

CEMENT EVALUATION CASED HOLE LOGGING COURSE

By : LUKAS UTOJO WIHARDJO FREELANCER

Proses Interpretasi Well Logging (Umum) CASED HOLE WELL LOG INTERPRETATION

OPEN HOLE WELL LOG INTERPRETATI ON :

LITHOLOGY, POROSITY & SATURATION

Cement Evaluation SATURATION PEN HOLE WELL LOG MONITORING PRODUCTION LOGGING

WATER FLOW LOGGING

Objectives of Primary Cementing Cement

Zonal Hydraulic-isolation

Gas Zone

Prevents

Oil Zone Shale Zone

• Mixing of unwanted fluids • Fluids escaping to surface • Invading fluids [crossflow] • Casing Corrosion • Casing Collapse

Water Zone

Casing

Cement Quality Problems No Zonal Hydraulic-isolation Cement

Oil Zone

It will potentially create : • Mixing of unwanted fluids • Fluids escaping to surface

• Invading fluids [crossflow] Water Zone

Casing

• Casing Corrosion • Casing Collapse

Environment Descriptions Fluid filled Annulus Top of Cement

Micro-Annulus b

Poor Cement to Formation Bond Formations Two stages Cement job Less than perfect cement job.

Double Casing

CBL-VDL Log Applications Client Needs Cement

To Evaluate Cement Job •Check Integrity of Cement

Oil Zone

•To Verify Zone Isolation •To Determine Cement Quality •Is there any Channel ? •Is it necessary to Repair ? •Will be possible to Repair?

Water Zone

Casing

[ by performing a SQUEEZE] •Where is the Top of the Cement ?

CBL-VDL Cement Bond Logging

Physics of Measurement

Basic Sonic Principle Basic Tool Principle – A Transmitter fires an acoustic signal in all directions – Surrounding Media Resonates – Receivers record resulting sound – Sound wave is analyzed

Basic CBL Principle Similar to a Ringing Bell No Cement

Good Bond

 When Fluid is behind Casing, pipe is free to vibrate [ loud sound ]  When the casing is bonded to hard cement, casing vibrations are attenuated proportionally to bonded surface

CBL Measurement Principle Tx

Basic Tool Configuration  1 Transmitter – 2 Receivers

3 ft

3 ft Receiver for CBL Measurement  5 ft Receiver for VDL Analysis  TOOL MUST BE CENTRALIZED 

R3

R5

5 ft

CBL: CEMENT BOND LOG VDL: VARIABLE DENSITY LOG

CBL-VDL Measurement Principle Acoustic Signal Amplitude

T0 |--- Resulting Sound--|

Time ms

- T0 : Firing Pulse - Resulting Sound wave : as recorded at the Receivers

CBL Measurement Principle CBL Definition Amplitude of First Arrival in mV  Measured at 3 ft Receiver  It is a function of the Casing-Cement Bond 

Tx

3 ft R3

R5

Transit Time Definition • Time elapsed from T0 to First detected Arrival (above threshold level) • T T is used as Log Quality Control Indicator

CBL Qualitative Meaning No Good Cement Bond

HIGH CBL signal strength => pipe is free to vibrate [no cement ] LOW CBL signal strength => attenuated energy [cement is present]

Sound to Signal • Magnetostrictive transducer (Tx) A high current is passed through a coil surrounding a magnetic material introducing a strain and causes a ticking sound (Joule effect)

DL / L • Piezoelectric transducer

(Rx)

Polarized ceramic crystals in the sonde produce voltage when exposed to strain (Villari effect) strain Unstrained crystal

voltage

CBL Amplitude Vs. Receivers Spacing

CBL-VDL Cement Bond Logging Gates Settings

NMSG CBLG

CBL Measurement Gates WARNING - The CBL represents one of the most common logs prone to human error - Incorrect setting of parameters can cause an invalid log - The CBL values are “fluid compensated” if the free pipe values are adjusted to the expected free pipe value in water , this is done either : 1- If the FCF is known and CBLF is presented 2- If the free pipe check is performed and amplitudes are adjusted (CBAF) to read the expected fee pipe value in water

CBL Measurement T0_Delay Mode (Fixed Gate Mode)

NMSG CBLG

NMSG: Near Minimum Sliding Gate CBLG : CBL Gate View the waveform and check the transit time value Set NMSG at measured/viewed T T – 10 ms Opens at NMSG and lasts CBLG ms

CBL Measurement TX Mode (Back-up for the T0_Delay Mode) TTSL

AMSG SGW SGCW

SGW: Sliding-Gate Width

SGCW : Sliding-Gate Closing Width

Sliding Gate opens at SGW ms BEFORE previous detected TT and closes

SGCW ms after current TT

Amplitude is CBSL,

AMSG : Auxiliary Minimum Sliding Gate Transit Time is TTSL

The VDL Signal VDL: VARIABLE DENSITY LOG  5 ft Receiver for VDL Analysis  Allows easy differentiation between casing and formation arrivals

Tx

R3

R5

5 ft

VDL Algorythm Principle • Recorded Waveform at one depth • Waveform is cut for only Positive Peaks

• Peaks are compared to a Grey Scale • Peaks are shaded and presented from Top View • Final Picture Vs Depth is obtained

Propagation of the Acoustic Energy distance Velocity =

time

Slowness

1

Slowness =

time

= velocity

distance

Time required for sound to travel 1 foot DT Casing DT Cement DT Formation DT Fluid

= 57 msec/ft = 75 msec/ft ≈ 100 msec/ft ≈ 189 msec/ft

Propagation of the Acoustic Energy cont’d Acoustic impedance (Z) defined as: Z=r.v

Z1 Z2

r: density of material

Water Steel Cement Sound

1. If Z1/Z2 is high ==> low transmittance 2. If Z1/Z2 is low ==> high transmittance

V: velocity of sound on that material The amount of sound transmitted between two different materials depends on their acoustic impedance difference

Waveform Time Analysis 2”

CASING ARRIVALS TRAVEL TIME

DT Casing = 57 msec/ft DT Cement = 75 msec/ft DT Formation ≈ 100 msec/ft DT Fluid ≈ 189 msec/ft

TTC = FLUID + CASING + FLUID = 3/12 in x 189 ms/ft + 3 ft x 57 ms/ft + 3/12 in x 189 ms/ft

=

265.5 ms

Waveform Time Analysis 2”

FORMATION ARRIVALS TRAVEL TIME TTF

DT Casing DT Cement DT Formation DT Fluid

= 57 msec/ft = 75 msec/ft ≈ 100 msec/ft ≈ 189 msec/ft

= FLUID + CEMENT + FORMATION + CEMENT + FLUID = 2x (3 in / 12 x 189 ms/ft + 2 in / 12 x 75 ms/ft) + 3 ft x 100 ms/ft =

419.5 ms

Waveform Time Analysis 2”

FLUID ARRIVALS TRAVEL TIME

DT Casing DT Cement DT Formation DT Fluid

TTf = FLUID = 3 ft x 189 ms/ft

=

567.0 ms

= 57 msec/ft = 75 msec/ft ≈ 100 msec/ft ≈ 189 msec/ft

CBL-VDL Standard Outputs Presentation • Transit Time TT in micro-seconds

[ms]

• CBL Amplitude in millivolts

[mV]

• VDL Variable Density Log [waveform visual representation] 400

TT

200 0

[ms]

CCL

GR

CBL [mV]

100 200

VDL [ms]

1200

CBL-VDL Standard Outputs • Transit Time TT in micro-seconds

[ms]

Log Quality Control • CBL Amplitude in millivolts

[mV ]

Quantitative Measurement of waveform energy • VDL Variable Density Log

[wafeform visual representation]

 Qualitative Analysis of sound  Qualitative indicator of the presence of solid materials between the casing and the formation • Gamma Ray and CCL as auxiliary curves for Correlation

CBL-VDL Cement Bond Logging

Factors affecting the Log E1 T0

Threshold TT TT’ DT

Free Pipe Signal Good Bond Signal

Stretching E1 T0

Free Pipe Signal Good Bond Signal

Threshold TT TT’

DT

In cases of Good Cement E1 decreases and TT is detected on a non linear portion of E1 DT STRETCHING is the TT increase from its value in free pipe

TT Cycle Skipping E1 T0

E3

Threshold TT’

TT

E2

In cases of very Good Cement E1 could not reach Detection Threshold Level T T skips to 3rd Peak [E3 ]........this is known as CYCLE SKIPPING

CBL-VDL Cement Bond Logging Basic Interpretation

CBL Qualitative Interpretation CONDITION

TRANSIT TIME

CBL AMPLITUDE

NORMAL

HIGH

Casing Arrivals Usually No Formation Arrivals

Good Bond to Casing & Formation

NORMAL to HIGH / NOISY

LOW

No Casing Arrivals Formation Arrivals

Good Bond to Casing Not to Formation

NORMAL to HIGH CAN BE NOISY

LOW

No Casing Arrivals No Formation Arrivals

Poor Bond to Casing

NORMAL

MEDIUM to HIGH

Strong Casing Arrivals No Formation Arrivals

Microannulus

NORMAL

MEDIUM to HIGH

Formation Arrivals Casing Arrivals

Channeling

NORMAL

MEDIUM to HIGH

Formation Arrivals Casing Arrivals

Fast Formations

LOW

HIGH

Formation Arrivals No Casing Arrivals

Eccentered Tool

LOW

LOW

DEPENDS

Free Pipe

VDL

Free Pipe Amplitude 5

 If no Casing-Cement bond,

amplitude is not attenuated  This is called 3

FREE PIPE AMPLITUDE

2

CBL: Free Pipe

T

CBL AMPLITUDE VS. CASING SIZE Values in Water

CBL Interpretation

FREE PIPE CHECK 100

100

Perfect

Chevron Patterns

Depth Match

Chevron Patterns

TT and CBL Amplitude as expected according to Casing Size

Cement to Casing Bond 5

 If casing is well bonded,

soundwave will be attenuated  The received CBL amplitude 3

2

will be low CBL: Free Pipe CBL: Good Bond

T

Open-Hole VDL’s (Before Casing)

GR

WF1 VDL (Standard VDL)

WF2 VDL

Cased-Hole VDL’s (After Casing)

GR

CCL

WF1 VDL (Standard VDL)

WF2 VDL

GOOD BOND TO CASING & FORMATION

X

Formation Arrivals

Transit Time

Low

with some Stretching