5-Cementing Basics + Evaluation

Cementing Basics

Why Cementing?

• Wellbore cement that provides complete zonal isolation protects the environment, enhances drilling safety and optimizes production. Without high-quality cement filling the annulus between the casing and the formation, freshwater aquifers above or below the reservoir might be contaminated by fluid from other formations. Casing that is not protected by cement might be prone to corrosion by formation fluids.

Cementing

• Reasons for quality cementing job:

– Support the pipe in place

• Further drilling

• Production

– Protect pipe in place

• Corrosive formation fluids

– Hydraulic isolation

• No communication between different formation fluids

• No migration of formation fluids to surface

• No loss of production to thief zones

– Data gathering• Borehole geometry (bit size, caliper, % excess, depth, etc.)

• Well bore information (pore and frac pressures, lithologies)

• Temperature (gradient, BHST, BHCT)

• Problem zones (lost circulation, washouts, water flow, etc.)

• Casing data (size, type and placement of hardware, previous casing)

• Survey data (TVD, KOP, bearing, deviation, etc.)

• Drilling fluid Data (type, density, rheology)

– Lab verification• Cement material is suitable for downhole condition

• Cement additives are suitable for downhole condition

• Cement system is reproducible

– Cement job simulation• For consistency and optimization of casing centering and mud removal

• Cement placement

Cementing Process (Job Design)

Cementing Process (Execution & Evaluation)

• Job execution– Reproduce the cement system verified by the Lab

– Flow rate for effective well clean and mud removal

– Duration of cement placement (pumpable slurry)

– Enough slurry volume

– Solid Fraction Monitoring for constant density

• Job evaluation– Hydraulic isolation and cement distribution

– Pipe condition

– Pipe support

Factors Affecting Cement Quality

• Borehole Geometry– It has a great effect on

the cement quality, good cement quality and good zonal isolation are achievable in good holes. In gauge holes allows:

• Cement volume

• Tubular centralization

• Effective flow rate for mud removal

Thin, impermeable mud filter cake(not gelled or unconsolidated)

Uniform as possible( no washouts or restrictions)

Casing centered in borehole

BHST at top ofCement >BHCTat TD

Annular gapMinimum: 3/4-in.Ideal: 1 1/2-in.

Properly conditionedhole and mud

Gaugediameter

No sloughing

NO FLOWNO LOSSES

Accurate BHST and BHCT

Factors Affecting Cement Quality – Cont.

• Borehole effect on cement / excess volume calculation

Correct volume

One-arm caliper

Wrong volume

Four-arm caliper

Two Equal DiametersCorrect volume

Different DiametersCorrect volume

Wrong volume

• Tubular centralization

– Effect on flow rate

1816141210864200 20 40 60 80 100

% Stand-off = wRH - RCX 100

API % STAND-OFF

Factors Affecting Cement Quality – Flow Types

V=2 x Vav

Laminar FlowVelocity Profile(Sliding motion)

Turbulent FlowVelocity Profile(Swirling motion)

Turbulent

There are four possibilitiesof flow in an Eccentric Annulus

No flowLaminarTurbulent

• Effect of flow rate on flow regimes

Narrow

Wide VwVn

Narrow

• Example10

ft75 100

Cement Coverage

25 50 75 100%

Pipe Standoff

Well10

ft75.0 100.0

Cement Coverage

25 50 75 100%

Pipe Standoff

ft75.0 100.0

Cement Coverage

25 50 75 100%

Pipe Standoff

Mud removal is the key to zonal isolation

CBL-VDL Cement Bond Logging

CBL-VDL (Physics of Measurement)

CBL-VDL_ Sónico: Principio Básico

Principio Físico Básico del Sónico:

– Un Transmisor T dispara señales acústicas omnidireccionalmente

– El Medio circundante Resuena

– Receptore captan las señales acústicas resultantes.

– Las Ondas de Sonidos son Analizadas

Principio Básico del CBL

Similar al resonar de una Campana

• Cuando no hay Cemento,

El Fluido esta detras del

Revestidor, Este esta libre

para Vibrar [ fuerte sonido]

• Cuando el revestidor esta

fuertemente adherido al

cemento , Las vibraciones

del casing son atenuadas

proporcionalmete a la

superficie cubierta.

GoodBond

GoodGoodBondBond

NoCement

NoNoCementCement

La cantidad de sonido transmitida entre dos

medios diferentes depende de su relación de

impedancias acústicas.

Cement

1. If Z1/Z2 es alta ==> baja transmisibilidad

1. If Z1/Z2 es baja ==> alta transmisibilidad

Impedancia Acústica (Z) se define como:

Z = ρ . v

ρ: densidad del medio

V: velocidad del sonido en el medio

Propagación de la Energía Acústica (2)

Principio de la Medición del CBL-VDL

Configuración Básica del Sónico:

• 1 Transmisor – 2 Receptores

– 3 ft Receptor para medida del CBL

– 5 ft Receptor para el Análisis VDL

• Herramienta DEBE estar CENTRALIZADA

CBL: CEMENT BOND LOG

VDL: VARIABLE DENSITY LOG

CBL-VDL Principio de Medición

Señal Acústica: (en cualquier de los Receptores)

Tiempoμs

Amplitud

- To: Pulso disparado

|--- Sonido Resultante--|

- Sonido Resultante: o señal acústica tal como se observa en los Receptores

CBL Principio de Medición

Definición del CBL:

• Amplitud de la Primera Cresta Recibida E1 en mV

• Medida en el Receptor a 3 ft

• Es función del Casing-Cement Bond3 ft

Definición del Tiempo de Transito:

• TT: Tiempo transcurrido desde T0 E1

• TT es utilizado en el control de calidad de

registro o LQC

CBL Principio de Medición

Significado Cualitativo del CBL

GoodBond

GoodGoodBondBond

NoCement

NoNoCementCement

Señal de CBL ALTA => Tuberia Revestidor Libre para Vibrar (No hay Cemento)

Señal de CBL BAJA => Atenuación de la Energia (Presencia de Cemento)

La Señal del VDL

VDL: VARIABLE DENSITY LOG

• Es el tren de onda sonica completo

• Medido en el Receptor 5 ft

• Su análisis permite fácil diferenciaciónentre las señales del casing y lasseñales de formación.

Principio Algorítmico del VDL

• Registro la forma de Onda en Profundidad

• Se toma solo la parte positiva de la Onda

• Las Crestas son comparadas con una Escala

de Grises. –Codificacion de intensidades-

• Las Crestas son sombreadas y presentadas

vistas desde arriba.

• Se obtiene la Imagen Final vs Profundidad:

ΔT Casing = 57 μsec/ftΔT Cement = 75μsec/ftΔT Formation ≈ 100 μsec/ftΔT Fluid ≈ 189 μsec/ft

Slowness (Tiempo de Tránsito)

Propagación de la Energía Acústica

distanciaVelocidad =

tiempo

1 tiempoSlowness = Δt = =

velocidad distancia

Tiempo requerido por el sonido para viajar 1 pie

Waveform Time Analysis

CASING ARRIVALS TRAVEL TIME

2”ΔT Casing = 57 μsec/ftΔT Cement = 75 μsec/ftΔT Formation ≈ 100 μsec/ftΔT Fluid ≈ 189 μsec/ft

TTC = FLUID + CASING + FLUID

3 in x 189 μs/ft 3 in x 189 μs/ft= + 3 ft x 57 μs/ft +

12 in/ft 12 in/ft

= 265.5 μs

FORMATION ARRIVALS TRAVEL TIME

TTF = FLUID + CEMENT + FORMATION + CEMENT + FLUID

3 in x 189 μs/ft + 2 in x 75 μs/ft= 2 x + 3 ft x 100 μs/ft

12 in/ft

= 419.5 μs

FLUID ARRIVALS TRAVEL TIME

TTf = FLUID

= 3 ft x 189 μs/ft

= 567.0 μs

CBL-VDL Standard Outputs Presentation

•Transit Time TT in micro-seconds [μs]

•CBL Amplitude in millivolts [mV ]

•VDL Variable Density Log [wafeform visual representation]

0 CBL 100

[mV]400 TT 200

200 VDL 1200

CBL-VDL (Factors Affecting the Log)

Stretching

E1 decreases and TT is detected on a non linear portion of E1

ΔT STRETCHING is the TT increase from its value in free pipe

In cases of Good Cement

Threshold

Free Pipe Signal

Good Bond Signal

TT Cycle Skipping

E1 could not reach Detection Threshold Level

T T skips to 3rd Peak [E3 ]........this is known as CYCLE SKIPPING

In cases of very Good Cement

Threshold

TT TT’

CBL Time Gates

E1 no alcanza el nivel de deteccion

T T salta al 3er ciclo [E3 ]........esto se conoce como SALTO DE CICLO

Threshold

TT TT’

CBL-VDL (Basic Interpretation)

Free Pipe Amplitude

• If no Casing-Cement bond,amplitude is not attenuated

CBL: Free Pipe

• This is called

FREE PIPE AMPLITUDE

CBL AMPLITUDE VS. CASING SIZE

CBL-VDL Fluid Effects

FREE PIPE CHECK

Interpretation

Chevron Patterns

Perfect

Depth Match

TT and CBL Amplitudeas expected according to Casing Size

Cement to Casing Bond

• If casing is well bonded,

soundwave will be attenuated

• The received CBL amplitude will be low

CBL: Free Pipe

CBL: Good Bond

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

Transit Time

with some

Stretching

Formation Arrivals

Casing Arrivals

<----------------------------------------CBL Amplitude

Irregular Bond

• The more “free” pipe or “contaminated” cement in an interval, the poorer the bond

• If cement job is not perfect, the amplitude decreases less

CBL: Poor Bond

POOR BOND

TO CASING

Stable

Transit Time

Strong

Casing Arrivals

Medium

<------------------------------CBL Amplitude

GOOD BOND CASING NOT TO FORMATION

Transit Time

with some

Cycle Skipping

Formation Arrivals

<----------------------------------------CBL Amplitude

Casing Arrivals

Micro Annulus

• Gap between Casing and Cement

Caused by contraction of casing aftercement sets if Casing Fluid is changed

• E1 amplitude resembles a poorer bond than actual

• Only a pressure pass can be done to eliminate the micro annulus

CBL: Poor Bond

Tool Eccentering

Causes for Eccentralization

• Improper Equipment selection

[ Centralizers ] for Casing Size

• Missing or Broken Centralizer(s)

• Weak Centralizers in deviated wells

• Tool Damaged and/or bent

• Damaged Casing

Consequences• Unbalanced sound paths

• Resulting waveform is meaningless

Eccentering Analysis

There will be destructive interference from different sound paths

Waveform from close tool side to casing

If the tool is eccentered

ThresholdT0

Short PathWaveformResulting Waveform

Waveform from far tool side to casing

Delayed Waveform

Result is a Bad Log

not recoverable

in Playback

Normal Waveform

Resulting waveform has Dramatic lower amplitude

Resembling a zone of Good Cementbut with shorter Transit Time [≈ 4 μs less]

CBL Amplitude Vs Tool Eccentering

Fast Formation Arrivals

In cases of good cement and

formation slowness < steel slowness

formation arrival arrives first

The transit time and CBL amplitude

will be affected

Fast Formation

ΔT Dolomite = 43.5 μsec/ftΔT Limestone = 47.5 μsec/ftΔT Anhydrite = 50.0 μsec/ft

FORMATION

<----------------------------------------CBL Amplitude

on areas of

fast formation

<---------------------------------------- arrivals

Transit Time

Shorter than

Casing arrivals

Interpretacion Cualitativa del CBL

Fuertes Arribos RevestidorNo Arribos de Formación

ALTANORMALCañería Libre

No Arribos RevestidorArribos de Formación

BAJAALTO (Saltos de ciclo y estiramiento)

Excelente cemento (adherencia al revestidor y a la formacion)

No Arribos RevestidorNo Arribos de Formación

BAJAALTO (Saltos de ciclo y estiramiento)

Buena adherencia al revestidorNo a la Formacion

Arribos RevestidorNo Arribos de Formación

MEDIA a ALTANORMALMala adherencia

Arribos de FormaciónArribos Revestidor

MEDIANORMALMicroanillo

Arribos de FormaciónArribos Revestidor

MEDIANORMALCanalizacion

Arribos de Formación No Arribos Revestidor

ALTABAJOFormaciones Rapidas

DEPENDEBAJABAJOHerramienta Excentralizada

VDLAMPLITUD del CBL

TIEMPO DE TRANSITO

CONDICION

CBL Quantitative Interpretation

• ATTENUATION

– Logarithm of E1 amplitude [first peak of CBL waveform]

• BOND INDEX

Attenuation in zone of interest [dB/ft]

Attenuation in Cemented Section [dB/ft]

Bond Index

Zone Insulation Based on Bond Index

55 66 77 88 99 1010

Bond Index = 70 %Bond Index = 70 %

Casing O.D. [in]

Interval

CBL Quantitative Interpretation

Casing Data

O.D. 7”, 29 lbm/ft

Cement Compresive

Strength

3000 psi

Casing Thickness

[from tables] .408 in

CBL value for 100% Bond

[minimum expected amplitude]

CBL Normalizing

• Ensures every sonde receiver is normalized to measure the same CBL value under the same conditions

– Receiver signal calibrated amplitude

– Special tube

– 500 psi of pressure

– Centralized sonde in tube

– Using box to fire

Transmitter

Upper head

Electronicssection

Water reservoir

Handpump

Fillvalve

Connect towater line

Plug H

Pump valve

Air release valve

CollarH

Support only at ends

Ejercicio 1 – Cementación CBL-VDL

Numérense de 1 a 4, los números pares se intercambian con los impares de la otra mesa.

Discutir cuales de estos argumentos son verdaderos y porque:

1 – El principal objetivo de la cementación es sostener la tubería

2 – El flujo laminar es mejor que el turbulento para cementar

3 – La centralización del CBL es muy importante pero un registro mal centralizado se puede corregir

4 – Los arribos de formación llegan antes que los de tubería.

5 – La presencia de microanillos indica un excelente cemento

6 – Es imprescindible normalizar el CBL para tener un buen registro

7 – La amplitud del CBL varia solamente por la presencia o ausencia de cemento.

8 – Cuando el CBL reduce su valor se debe siempre a la presencia decemento

Ultrasonic Radial Imager (OH/CH)

Ultra Sonic Imager (Physics of Measurement)

Theory of Measurement – Basic Principle

• UCS transducer acts as transmitter & receiver– Transmits short pulse of acoustic energy– Receives multiple echoes from the casing, cement &

formation • Casing Resonates from multiple reflections• Casing resonance dampened in the presence of cement

Mud Casing Cement FormationTransducer

Theory of Measurement

• The measured amplitude is a function of the acoustic impedance in the three media (mud, steel and outside medium). In the case of free pipe, the amplitude decay is slow. With cement behind the casing, the amplitude decay is fast because of the improved acoustic coupling between the steel and the outside medium.

Theory of Measurement

• Internal Radius and Thickness Calculations are derived from transit time measurements taken from the main ultrasonic transducer and the fluid properties transducer.

Technical Specifications

-2-1.5

-1-0.5

IST AN

CE (IN

0 1 2 3 4 5 6 7 8 9 10

AXIAL DISTANCE (INCHES)• The ultrasonic

transducer diameter is approx. 1.0”, therefore it can detect features that size or larger

• Optimum signal measurement is < 2.5” standoff

• 2µs Fire Pulse

Features & Benefits

• Identifies Presence of Channels, Large and Small

• Ignores Small Micro-annulus

• Not Sensitive to Fast Formations.

• Can be used to Evaluate Light Cements and Foam Cements (Recent Success)

• Provides Internal Casing Geometry and Casing Thickness

• 100% Azimuthal coverage

• Provides Open hole images in WBM & OBM

Ultra Sonic Imager (Interpretation and Examples)

GOOD CEMENT LOG EXAMPLE

FREE PIPE EXAMPLE

LIGHT CEMENT LOG VENEZUELA EXAMPLE

Well: RM-47

– 7” Liner

– 8.5” Bit Size

– OBM 10.2ppg

– Depth: 9418 ft.

– Temp: 246F

– Density Cement: 10.2

– 60% Nitrogen Spheres

– 0.6 Specific Gravity

– Compressive Strength

• 1200 lbs / 24

RAW OH IMAGE (CH Sensor – 400KHz)

PROCESSED IMAGE (CH Sensor – 400KHz)

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