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© 2006 Weatherford. All rights reserved.
Cementing Basics
© 2006 Weatherford. All rights reserved.
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.
© 2006 Weatherford. All rights reserved.
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
© 2006 Weatherford. All rights reserved.
– 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)
© 2006 Weatherford. All rights reserved.
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
© 2006 Weatherford. All rights reserved.
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
© 2006 Weatherford. All rights reserved.
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
Wrong volume
© 2006 Weatherford. All rights reserved.
Factors Affecting Cement Quality – Cont.
• Tubular centralization
– Effect on flow rate
1816141210864200 20 40 60 80 100
WW
% Stand-off = wRH - RCX 100
API % STAND-OFF
FLO
W R
ATE
RA
TIO
RC
RH
© 2006 Weatherford. All rights reserved.
Factors Affecting Cement Quality – Flow Types
V=0
V=2 x Vav
Laminar FlowVelocity Profile(Sliding motion)
Turbulent FlowVelocity Profile(Swirling motion)
© 2006 Weatherford. All rights reserved.
Factors Affecting Cement Quality – Cont.
Incr
easi
ng F
low
Rat
e
Turbulent
There are four possibilitiesof flow in an Eccentric Annulus
No flowLaminarTurbulent
• Effect of flow rate on flow regimes
© 2006 Weatherford. All rights reserved.
Factors Affecting Cement Quality – Cont.
Narrow
Wide VwVn
Wide
Narrow
© 2006 Weatherford. All rights reserved.
Factors Affecting Cement Quality – Cont.
© 2006 Weatherford. All rights reserved.
Factors Affecting Cement Quality – Cont.
• Example10
750
1100
011
250
1150
0
ft75 100
%
Cement Coverage
Cement Coverage
25 50 75 100%
Pipe Standoff
1/1
2/1
Well10
750
1100
011
250
1150
0
ft75.0 100.0
%
Cement Coverage
Cement Coverage
25 50 75 100%
Pipe Standoff
1/1
2/1
Well
© 2006 Weatherford. All rights reserved.
Factors Affecting Cement Quality – Cont.
1075
011
000
1125
011
500
ft75.0 100.0
%
Cement Coverage
Cement Coverage
25 50 75 100%
Pipe Standoff
1/1
2/1
Well
© 2006 Weatherford. All rights reserved.
Factors Affecting Cement Quality – Cont.
Mud removal is the key to zonal isolation
© 2006 Weatherford. All rights reserved.
CBL-VDL Cement Bond Logging
© 2006 Weatherford. All rights reserved.
CBL-VDL (Physics of Measurement)
© 2006 Weatherford. All rights reserved.
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
© 2006 Weatherford. All rights reserved.
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
© 2006 Weatherford. All rights reserved.
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
Propagación de la Energía Acústica (2)
© 2006 Weatherford. All rights reserved.
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
R3
R5
© 2006 Weatherford. All rights reserved.
CBL-VDL Principio de Medición
Señal Acústica: (en cualquier de los Receptores)
Tiempoμs
Amplitud
T0
- To: Pulso disparado
|--- Sonido Resultante--|
- Sonido Resultante: o señal acústica tal como se observa en los Receptores
R5ft
R3ft
Tx
© 2006 Weatherford. All rights reserved.
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
Tx
R3
R5
Definición del Tiempo de Transito:
• TT: Tiempo transcurrido desde T0 E1
• TT es utilizado en el control de calidad de
registro o LQC
TT
© 2006 Weatherford. All rights reserved.
CBL Principio de Medición
© 2006 Weatherford. All rights reserved.
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)
© 2006 Weatherford. All rights reserved.
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.
5 ft
Tx
R3
R5
© 2006 Weatherford. All rights reserved.
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:
© 2006 Weatherford. All rights reserved.
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
© 2006 Weatherford. All rights reserved.
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
© 2006 Weatherford. All rights reserved.
Waveform Time Analysis
FORMATION ARRIVALS TRAVEL TIME
2”ΔT Casing = 57 μsec/ftΔT Cement = 75 μsec/ftΔT Formation ≈ 100 μsec/ftΔT Fluid ≈ 189 μsec/ft
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
© 2006 Weatherford. All rights reserved.
Waveform Time Analysis
FLUID ARRIVALS TRAVEL TIME
2”ΔT Casing = 57 μsec/ftΔT Cement = 75 μsec/ftΔT Formation ≈ 100 μsec/ftΔT Fluid ≈ 189 μsec/ft
TTf = FLUID
= 3 ft x 189 μs/ft
= 567.0 μs
© 2006 Weatherford. All rights reserved.
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
© 2006 Weatherford. All rights reserved.
CBL-VDL (Factors Affecting the Log)
© 2006 Weatherford. All rights reserved.
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
T0
TT
Free Pipe Signal
TT’
ΔT
Good Bond Signal
© 2006 Weatherford. All rights reserved.
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
E1 E3
E2
T0
TT TT’
© 2006 Weatherford. All rights reserved.
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
E3
T0
TT TT’
© 2006 Weatherford. All rights reserved.
CBL-VDL (Basic Interpretation)
© 2006 Weatherford. All rights reserved.
Free Pipe Amplitude
• If no Casing-Cement bond,amplitude is not attenuated
CBL: Free Pipe
T
5
3
2
• This is called
FREE PIPE AMPLITUDE
© 2006 Weatherford. All rights reserved.
CBL AMPLITUDE VS. CASING SIZE
© 2006 Weatherford. All rights reserved.
CBL-VDL Fluid Effects
© 2006 Weatherford. All rights reserved.
FREE PIPE CHECK
CBL
Interpretation
Chevron Patterns
Chevron Patterns
Perfect
Depth Match
TT and CBL Amplitudeas expected according to Casing Size
100
100
© 2006 Weatherford. All rights reserved.
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
© 2006 Weatherford. All rights reserved.
Open-Hole VDL’s (Before Casing)
GR WF1 VDL(Standard VDL)
WF2 VDL
© 2006 Weatherford. All rights reserved.
Cased-Hole VDL’s (After Casing)
GR CCL WF1 VDL(Standard VDL)
WF2 VDL
© 2006 Weatherford. All rights reserved.
GOOD BOND TO
CASING
& FORMATION
X
X
Transit Time
with some
Stretching
Formation Arrivals
X
No
Casing Arrivals
Low
<----------------------------------------CBL Amplitude
© 2006 Weatherford. All rights reserved.
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
2
© 2006 Weatherford. All rights reserved.
POOR BOND
TO CASING
X
X
X
Stable
Transit Time
Strong
Casing Arrivals
Medium
<------------------------------CBL Amplitude
© 2006 Weatherford. All rights reserved.
GOOD BOND CASING NOT TO FORMATION
X
X
Transit Time
with some
Cycle Skipping
No
Formation Arrivals
Low
<----------------------------------------CBL Amplitude
No
Casing Arrivals
© 2006 Weatherford. All rights reserved.
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
T
5
3
2
© 2006 Weatherford. All rights reserved.
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• Unbalanced sound paths
• Resulting waveform is meaningless
© 2006 Weatherford. All rights reserved.
Eccentering Analysis
There will be destructive interference from different sound paths
Waveform from close tool side to casing
If the tool is eccentered
ThresholdT0
TT
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]
© 2006 Weatherford. All rights reserved.
CBL Amplitude Vs Tool Eccentering
© 2006 Weatherford. All rights reserved.
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/ftΔT Limestone = 47.5 μsec/ftΔT Anhydrite = 50.0 μsec/ft
© 2006 Weatherford. All rights reserved.
FAST
FORMATION
High
<----------------------------------------CBL Amplitude
on areas of
fast formation
<---------------------------------------- arrivals
Transit Time
Shorter than
Casing arrivals
© 2006 Weatherford. All rights reserved.
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
© 2006 Weatherford. All rights reserved.
CBL Quantitative Interpretation
• ATTENUATION
– Logarithm of E1 amplitude [first peak of CBL waveform]
• BOND INDEX
Attenuation in zone of interest [dB/ft]
BI =
Attenuation in Cemented Section [dB/ft]
© 2006 Weatherford. All rights reserved.
Bond Index
© 2006 Weatherford. All rights reserved.
Zone Insulation Based on Bond Index
55 66 77 88 99 1010
3030
2525
2020
1515
1010
55
Bond Index = 70 %Bond Index = 70 %
Bond Index = 60 %Bond Index = 60 %
Bond Index = 80 %Bond Index = 80 %
Casing O.D. [in]
Interval
[ft]
© 2006 Weatherford. All rights reserved.
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]
© 2006 Weatherford. All rights reserved.
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
SFT
Fillvalve
Connect towater line
Plug H
Pump valve
Air release valve
CollarH
Support only at ends
© 2006 Weatherford. All rights reserved.
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
© 2006 Weatherford. All rights reserved.
Ultrasonic Radial Imager (OH/CH)
© 2006 Weatherford. All rights reserved.
Ultra Sonic Imager (Physics of Measurement)
© 2006 Weatherford. All rights reserved.
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
© 2006 Weatherford. All rights reserved.
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.
© 2006 Weatherford. All rights reserved.
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.
© 2006 Weatherford. All rights reserved.
Technical Specifications
-2-1.5
-1-0.5
00.5
11.5
2R
AD
IAL D
IST AN
CE (IN
CH
ES)
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
© 2006 Weatherford. All rights reserved.
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
© 2006 Weatherford. All rights reserved.
Ultra Sonic Imager (Interpretation and Examples)
© 2006 Weatherford. All rights reserved.
GOOD CEMENT LOG EXAMPLE
© 2006 Weatherford. All rights reserved.
FREE PIPE EXAMPLE
© 2006 Weatherford. All rights reserved.
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
© 2006 Weatherford. All rights reserved.
RAW OH IMAGE (CH Sensor – 400KHz)
© 2006 Weatherford. All rights reserved.
PROCESSED IMAGE (CH Sensor – 400KHz)
© 2006 Weatherford. All rights reserved.