cggv seismic pore pressure prediction
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EAGE 2004 - Seismic Pore Pressure Prediction 1
Seismic Pore Pressure PredictionEAGE, Paris 2004
Jean-Luc Formento
2EAGE 2004 - Seismic Pore Pressure Prediction
Seismic Pore Pressure Prediction
Seismic solution for predicting drilling hazards
EAGE 2004 - Seismic Pore Pressure Prediction 3
Outline
Pore Pressure Concepts
Seismic Processing – HDPIC technology
Filtering and Calibration of Velocity Cube
Pore Pressure Estimation
EAGE 2004 - Seismic Pore Pressure Prediction 4
Pore Pressure Concepts
- =
Total Vertical StressOver Burden Effective stressPore Pressure
Lithostatic Load+
Fluid ColumnMatrixPore Fluids
Stress equation σtotal – PP = σ’effective
Different methods can be used to relate σ’effective to velocity
Terzaghi
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Over pressure Mechanisms
Under compaction+
Secondary Mechanism
Under- compaction
Compaction Overburden Gradient
Top Overpressure
PP
Effectivestress
Fluid expansion
8.3 -9 ppg
10-14 ppg
> 15 ppg
Bowers GL, 2001
Pore Pressure Gradient
Why Predict Pore Pressure?
OBG = overburden gradient
FG = fracture gradient
PPG = pore pressure gradient
MD = mud weight gradient real
MD = mud weight gradient ideal
Well stability risks,‘blow out’
Losing mud and fracture risk
DamagingReservoir risks
Key requirement for safe well planning in over-pressured formations
depth
pressure
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PP = OBG - (OBG – GHyd ) * (Vintobs /Vintnor)x
PP = Pore Pressure gradient(ppg or psi/ft)OBG = Overburden Gradient (ppg or psi/ft)ρ(z) = Density from Gardner relationGhyd = Hydrostatic gradientVintnor = Normal Compaction Trend for interval velocity (m/s)Vintobs = Interval velocity observed (m/s)X = Exponent
Eaton’s Method
How to relate pore pressure to seismic velocity?
Vintnor
Vint
Dep
th
Vintobs
Effective stress gradient
( )bmudlineVVa
1
int1 −=σ
PPpressure = OB vertical stress - Effective stress σBower’s Method
1500170019002100230025002700290031003300
0.5 0.7 0.9 1.1 1.3
(g)
V = 2575* (Esfuerzo effect)1.4323Effective Stress
Bowers assumes an Effective stress σ - velocity relationship
∫z
dzzz 0
).(1 ρ
Where Vint = Interval velocity observed (m/s)Vmudline = cste (m/s)
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The General Workflow
Calibration Pore Pressure Gradient with existing wells
Estimation and Calibration of 3D Velocity cube
Apply HDPIC high resolution automatic velocity picking
Perform Geostatistical Filtering (GSFIL)
Calibrate seismic interval velocitiesto well rock velocities
Convert Vint cube from time to depth
Analyze drilling history of wells
Analyze compaction regime and estimate trend
Calculate Overburden Gradient OBG, Pore Pressure Gradient PPG and
Fracture Gradient FG from Drilling data
Estimate Effective Stress and Correlation with Vint
Transform Vint cube into Effective Stress Cube
Compute OBG cube, then PPG cube and FG cube
Extract OBG, PPG and FG profiles at new drilling locations
EAGE 2004 - Seismic Pore Pressure Prediction 8
Outline
Pore Pressure Concepts
Seismic processing – HDPIC technology
Filtering and Calibration of Velocity Cube
Pore Pressure Estimation
EAGE 2004 - Seismic Pore Pressure Prediction 9
Seismic processing – HDPIC technology
HDPIC = High-Density Anisotropic Velocity AnalysisHigh density accurate Geological Velocity (RMS) fieldsTwo parameter picking (V and η) Picking independent from muteConfidence (semblance) associated to each picked point
internal QC and editing of the picked values are performed
Vnmo = VRMS η
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HDPIC overview
Near offset data(offset/depth≈0.5)
Full offset data
Standard Velocity Analysis
Bispectral Velocity Analysis
Hyperbolic Moveoutone parameter: V
Tim
e
Velocity
Non Hyperbolic Moveouttwo parameters picked
Tim
e
dtnτ0
Vrms < Vstack
(curvature at 0°)
Vrms = f(time, dtn τ0)η = f(time, τ0)
(offset/depth<2.5)
StackingVelocity
Stacking(dtn τ0) pair
Geological Velocity(RMS)
direct estimation
Vrms = 95%Vstack
EAGE 2004 - Seismic Pore Pressure Prediction 11
Outline
Pore Pressure Concepts
Seismic processing – HDPIC technology
Filtering and Calibration of Velocity Cube
Pore Pressure Estimation
EAGE 2004 - Seismic Pore Pressure Prediction 12
Geostatistical Filtering of Velocity CubeRaw interval velocity section
Final interval velocity section
The 3D geostatistical filtering:
removes the residual noise from the automatic velocity picking
prevents anomalous interval velocity values
preserves main geological features
Filtered RMS velocity volume is converted into interval velocity volume, which is the key parameter in the pore pressure workflow
EAGE 2004 - Seismic Pore Pressure Prediction 13
Calibration of the Velocity Cube
WorkflowMatch seismic velocity to sonic logs, check shots and geological tops when available.
• Calculation of seismic interval velocity (VIhz ) in each macro layer
• Calculation of well interval velocity from checkshots
• Estimation of VIhz correction coefficients for each interval to match the
wells
• Correction of the velocity cube by macro interval
• Calibrated velocity cube used for:
– Time-depth conversion
– Density estimation (Gardner)
– Vintobs (Eaton, Bowers,..)
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Interval velocitybefore
calibration
Calibrated interval velocity
Calibration
Transformation into average velocity
Time/depth conversion
Average velocity
time
depth
Calibration of the Velocity Cube
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Outline
Pore Pressure Concepts
Seismic processing – HDPIC technology
Filtering and Calibration of Velocity Cube
Pore Pressure Estimation
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Methodology• Used to derive the Overburden gradient ( key parameter of Terzaghi equation)
• Different techniques can be used according to well data available
Estimation of density using compaction law with depth
Estimation of density from Vint with modified Gardner equation at each well location and 3D kriging by macro intervals: Rho =Rho(0) + A*(Vint-V0)B => density trend cube
Density cubes obtained using different geostatistical algorithms (wells as hard data and density trend as soft data)
Estimation of the Density Cube
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
1 1.5 2 2.5 3
Density (g/cc)
Dep
th (m
)
Density from Gardner
Density from log
Density cube
OBG cube
∫z
dzzz 0
).(1 ρ
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Pore Pressure Cube Generation
Pore Pressure analysis at each well location using PP indicator, geological and drilling reportsDefine overpressure mechanismDefine relationship between interval velocity observed and effective stress (Eaton, Bowers,…)
Pore Pressure profile from Vint
Overburden gradient OBG
Vintnor Definition:Low caseBest caseHigh Case
( )bmudlineVVa
1
int1 −=σBowers: PP = OBG - (OBG – GHyd ) * (Vintobs /Vintnor)xEaton:
Vintobs
Pore Pressure indicator
PP = OBG - Effective stress
EAGE 2004 - Seismic Pore Pressure Prediction 18
Pore Pressure Cube Generation
OBG - Effective stress = Pore Pressure
OBG
Effective stress
Pore Pressure
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Predictions at future well locations
From the 3D cube, OBG, PPG and FG can be extracted at any new location. Over-pressured zones are interpreted in their structural and seismic stratigraphy framework.
Top Over-pressured zone
PPG cube
Seismic Amplitude cube Extraction of Pore pressure cubes around
new well locations
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PP low case (ppg)
Uncertainty assessment: sensitivity cubes
PP high case (ppg)
PP best case (ppg)
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The CGG workflow
Careful well calibration of key geopressure parameters by geomechanical experts
Improvement in pore pressure prediction resolution using CGG’s High density anisotropic velocity
analysis
Advanced geostatistical techniques to derive rock properties and calibrate seismic and well
velocities
3D GOCAD geo-modelling technology for 3D estimations and predictions at new well location
Provides:
Detection of problematic drilling zones
Pre-drill pore pressure profiles along planned well trajectories
Multiple scenarios with Pore Pressure confidence margins