5-Cementing Basics + Evaluation

(1)

(2)

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.

(3)

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

(4)

–

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

Cementing Process (Job Design)

(5)

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

(6)

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 of

Cement >BHCT

at TD

Annular gap

Minimum: 3/4-in.

Ideal: 1 1/2-in.

Properly

conditioned

hole and mud

Gauge

diameter

No sloughing

NO FLOW

NO LOSSES

Accurate BHST and BHCT

(7)

Factors Affecting Cement Quality – Cont.

• Borehole effect on cement / excess volume calculation

Correct volume

One-arm caliper

Wrong volume

Four-arm caliper

Two Equal Diameters

Correct volume

Different Diameters

Correct volume

Wrong volume

(8)

Factors Affecting Cement Quality – Cont.

• Tubular centralization

–

Effect on flow rate

18

16

14

12

10

8

6

4

2

0 0 20 40 60

80 100

W

% Stand-off =

_R

w

H

- R

C

X 100

API % STAND-OFF

FLOW RATE RATIO

R

C

(9)

Factors Affecting Cement Quality – Flow Types

V=0

V=2 x V

_av

Laminar Flow

Velocity Profile

(Sliding motion)

Turbulent Flow

Velocity Profile

(Swirling motion)

(10)

Factors Affecting Cement Quality – Cont.

Increasing Flow Rate

_Tu

rb

ul

en

t

There are four possibilities

of flow in an Eccentric Annulus

No flow

Laminar

Turbulent

• Effect of flow rate on flow regimes

(11)

Factors Affecting Cement Quality – Cont.

Narrow

Wide

V

_w

V

_n

Wide

Narrow

(12)

(13)

Factors Affecting Cement Quality – Cont.

• Example

10750

11000

11250

11

500 ft

75

100 %

Cement Coverage

25

50

75

100 %

Pipe Standoff

1/1 2/1

Well

10750

11000

11250

11

500 ft

75.0

100.0 %

Cement Coverage

25

50

75

100 %

Pipe Standoff

1/1 2/1

Well

(14)

Factors Affecting Cement Quality – Cont.

10

750 11000

112

50

0 ft

75.0

100.0 %

Cement Coverage

25

50

75

100 %

1/1

(15)

Factors Affecting Cement Quality – Cont.

(16)

(17)

(18)

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

T

R

(19)

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.

Good

Bond

Good

Bond

No

Cement

No

Cement

(20)

La cantidad de sonido transmitida entre dos

medios diferentes depende de su relación de

impedancias acústicas.

Water

Steel

Cement

Sound

Z1

Z2

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

(21)

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

3 ft

5 ft

Tx

R

₃

(22)

CBL-VDL Principio de Medición

Señal Acústica: (en cualquier de los Receptores)

Tiempo

μs

Amplitud

T

0 - To:

Pulso disparado

|--- Sonido Resultante--|

- Sonido Resultante: o señal acústica tal como se

observa en los Receptores

R

5ft

R

3ft

T

x

(23)

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 Bond

3 ft

Tx

R

₃

R

₅

Definición del Tiempo de Transito:

• TT: Tiempo transcurrido desde T

₀

Æ

E1

• TT es utilizado en el control de calidad de

registro o LQC

(24)

(25)

Significado Cualitativo del CBL

Good

Bond

Good

Bond

No

Cement

No

Cement

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

(26)

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 diferenciación

entre las señales del casing y las

señales de formación.

5 ft

Tx

R

₃

(27)

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.

(28)

ΔT Casing

= 57

μsec/ft

ΔT Cement

= 75

μsec/ft

Slowness (Tiempo de Tránsito)

Propagación de la Energía Acústica

distancia

Velocidad =

tiempo

1 tiempo

Slowness = Δt = =

velocidad distancia

Tiempo requerido por el sonido para

viajar 1 pie

(29)

Waveform Time Analysis

CASING ARRIVALS

TRAVEL TIME

2”

ΔT Casing

= 57

μsec/ft

ΔT Cement

= 75

μsec/ft

ΔT Formation ≈ 100 μsec/ft

ΔT Fluid

≈ 189

μsec/ft

TT

_C

= FLUID + CASING + FLUID

3 in x 189 μs/ft

=

+ 3 ft x 57

μs/ft +

12 in/ft

(30)

Waveform Time Analysis

FORMATION ARRIVALS

TRAVEL TIME

2”

ΔT Casing

= 57

μsec/ft

ΔT Cement

= 75

μsec/ft

ΔT Formation ≈ 100 μsec/ft

ΔT Fluid

≈ 189

μsec/ft

TT

_F

= 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

(31)

Waveform Time Analysis

FLUID ARRIVALS

TRAVEL TIME

2”

ΔT Casing

= 57

μsec/ft

ΔT Cement

= 75

μsec/ft

ΔT Formation ≈ 100 μsec/ft

ΔT Fluid

≈ 189

μsec/ft

TT

_f

= FLUID

= 3 ft x 189 μs/ft

=

567.0 μs

(32)

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

[μs]

200 VDL 1200

[μs]

GR

CCL

(33)

(34)

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

E1

T

₀

TT

Free Pipe Signal

TT’

ΔT

(35)

TT Cycle Skipping

E1 could not reach Detection Threshold Level

T T skips to 3

rd

_{Peak [E}

3 ]...this is known as

CYCLE SKIPPING

In cases of very Good Cement

Threshold

E1

_E3

E2

T

₀

(36)

CBL Time Gates

E1 no alcanza el nivel de deteccion

T T salta al 3er ciclo [E

₃

]...esto se conoce como

SALTO DE CICLO

Threshold

E3

T

₀

(37)

(38)

Free Pipe Amplitude

• If no Casing-Cement bond,

amplitude is not attenuated

CBL: Free Pipe

T

5

3

2

• This is called

(39)

(40)

(41)

FREE PIPE CHECK

CBL

Interpretation

Chevron Patterns

Perfect

Depth Match

TT and CBL Amplitude

as expected according to Casing Size

100

(42)

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

T

5

3

2

(43)

Open-Hole VDL’s (Before Casing)

GR

WF1 VDL

(Standard VDL)

(44)

(45)

GOOD BOND TO

CASING

& FORMATION

X

Transit Time

with some

Stretching

Formation Arrivals

X

No

Casing Arrivals

Low

<---CBL Amplitude

(46)

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

T

5

3

(47)

POOR BOND

TO CASING

X

Stable

Transit Time

Strong

Casing Arrivals

Medium

<---CBL Amplitude

(48)

GOOD BOND

CASING NOT

TO FORMATION

X

Transit Time

with some

Cycle Skipping

No

Formation Arrivals

Low

<---

CBL Amplitude

No

Casing Arrivals

(49)

Micro Annulus

• Gap between Casing and Cement

Caused by contraction of casing after

cement 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

T

5

3

(50)

Tool Eccentering

Causes for Eccentralization

5

3

2 T

• 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

(51)

Eccentering Analysis

There will be destructive interference from different sound paths

Waveform from close tool side to casing

If the tool is eccentered

Threshold

T

₀

TT

Short Path

Waveform

Resulting 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

(52)

(53)

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

T

5

3

2 ΔT Dolomite = 43.5 μsec/ft

ΔT Limestone = 47.5 μsec/ft

ΔT Anhydrite = 50.0 μsec/ft

(54)

FAST

FORMATION

High

<---

CBL Amplitude

on areas of

fast formation

Transit Time

Shorter than

Casing arrivals

(55)

Interpretacion Cualitativa del CBL

Fuertes Arribos Revestidor

No Arribos de Formación

ALTA

NORMAL

Cañería Libre

No Arribos Revestidor

Arribos de Formación

BAJA

ALTO (Saltos

de ciclo y

estiramiento)

Excelente cemento (adherencia al

revestidor y a la formacion)

No Arribos Revestidor

No Arribos de Formación

BAJA

ALTO (Saltos

de ciclo y

estiramiento)

Buena adherencia al revestidor

No a la Formacion

Arribos Revestidor

No Arribos de Formación

MEDIA a ALTA

NORMAL

Mala adherencia

Arribos de Formación

Arribos Revestidor

MEDIA

NORMAL

Microanillo

Arribos de Formación

Arribos Revestidor

MEDIA

NORMAL

Canalizacion

Arribos de Formación

No Arribos Revestidor

ALTA

BAJO

Formaciones Rapidas

DEPENDE

BAJA

BAJO

Herramienta Excentralizada

VDL

AMPLITUD del

CBL

TIEMPO DE

TRANSITO

CONDICION

(56)

CBL Quantitative Interpretation

• ATTENUATION

–

Logarithm of E1 amplitude [first peak of CBL waveform]

• BOND INDEX

Attenuation in zone of interest [dB/ft]

BI =

(57)

(58)

Zone Insulation Based on Bond Index

30

25

20

15

10

5

5 Bond Index = 70 %

Bond Index = 70 %

Bond Index = 60 %

Bond Index = 80 %

I

n

t

e

r

v

a

l

[ft]

(59)

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]

(60)

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

Electronics

section

Water

reservoir

Hand

pump

SFT

Fill

valve

Plug H

Pump valve

Air release valve

Collar

H

(61)

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 de

cemento

(62)

(63)

(64)

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 Formation

Transducer

(65)

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.

(66)

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.

(67)

Technical Specifications

-2

-1

.5

-1

-0

.5

0

0.5

1

1.5

2 R

A

D

IA

L

D

IS

T

A

N

C

E

(I

N

C

H

E

S

)

0

1

2

3 AXIAL DISTANCE (INCHES)

4

5

6

7

8

9

10

• The ultrasonic

transducer diameter

is approx. 1.0”,

therefore it can

detect features that

size or larger

• Optimum signal

measurement is <

2.5” standoff

(68)

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

(69)

(70)

(71)

(72)

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

(73)

(74)

(75)