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New Mexico CO2 Project
� Outline
� VSP Processing review
� Baseline Surveys review
� Monitor Surveys review
� Time-lapse discussion
Les NuttBorehole Seismic Ops Manager
Ric SmithSenior Geophysicist
WALKAWAYWALKAWAYWALKAWAYWALKAWAYWALKABOVEWALKABOVEWALKABOVEWALKABOVEZERO OFFSETZERO OFFSETZERO OFFSETZERO OFFSETCHECKSHOTCHECKSHOTCHECKSHOTCHECKSHOT
SALT PROXSALT PROXSALT PROXSALT PROX
Borehole Seismic Survey Types
CCCCROSS WELLROSS WELLROSS WELLROSS WELL
OFFSETOFFSETOFFSETOFFSET
Pp
Ps
3D VSP3D VSP3D VSP3D VSP SINGLE WELLSINGLE WELLSINGLE WELLSINGLE WELL
PASSIVEPASSIVEPASSIVEPASSIVE
MMMMONITORINGONITORINGONITORINGONITORING
BOREHOLE SEISMIC SURFACE SEISMIC
GEOPHONESGEOPHONESGEOPHONESGEOPHONES
SOURCE
REFLECTOR
GEOPHONEGEOPHONEGEOPHONEGEOPHONE(S)(S)(S)(S)
MAXISMAXISMAXISMAXIS
SOURCE
REFLECTOR
Tim
e
De
pth
& T
ime
Borehole versus Surface Seismic
LATERAL RESOLUTIONLATERAL RESOLUTIONLATERAL RESOLUTIONLATERAL RESOLUTION
r ~ ((((λλλλ....ab/(a+bab/(a+bab/(a+bab/(a+b)))) ) ) ) ) 1/21/21/21/2
SOURCE
de
pth
aaaa
r = radius of the first order Fresnel Zone
rrrr
VERTICAL RESOLUTIONVERTICAL RESOLUTIONVERTICAL RESOLUTIONVERTICAL RESOLUTION
∆∆∆∆ZZZZ ~ λ /4= V/(4f)= V/(4f)= V/(4f)= V/(4f)
bbbb
GeophoneGeophoneGeophoneGeophone
Surface seismicSurface seismicSurface seismicSurface seismicVSPVSPVSPVSP
35 Hz 15 Hz
Reflector pointReflector pointReflector pointReflector point
Geophone from target
Target Depth
Velocity (m/s)
Dominant Frequency
(Hz)
Radius of Fresnel Zone
(m)1000 2000 2000 50 163100 2000 2000 50 6210 3000 3000 30 32
Borehole versus Surface Seismic
Zero Offset VSP
As for Checkshot
survey
As for Checkshot
survey
Over-pressure
Zone Prediction
Over-pressure
Zone Prediction
Multiple Pattern
Identification
Multiple Pattern
Identification
Independent
Pp & Ps Seismic
answer at the
well
Independent
Pp & Ps Seismic
answer at the
well
Corridor
Stack
Surface
SeismicDe
pth
(m
)
Time (s)
Source
Ge
op
ho
ne
s
Depth Model
Overpressure
onset
Intermediate
TD
……
ZERO OFFSETZERO OFFSETZERO OFFSETZERO OFFSET
Basic VSP Processing
� Outline
� Transit Time Calculations
� Basic VSP Processing
� Transit Time Calculation
Depth
TimeSurface Seismic VSP
Transit
Time (TT)
TT
Reflection
Time (OWT)OWT
TT
TWT = OWT + TT
Reflection
TWT
TWT
One-Way Time vs. Two Way Time
Depth
Time
VSP minus Transit Time (-TT)
Depth
TimeTWTTWTTWTTWT
VSP plus Transit Time (+TT)
Basic VSP Processing
� Data preparation
� Stacking Techniques
� Wavefield separation
� Deconvolution
� Corridor Stack
� Data Preparation
Wavefield
Separation
Deconvolution
Processing Sequence
SRD, BPF, TAR
Normalisation
Corridor
Stack
Median
StackData Edit
Upgoing
Wavefield
Downgoing
Wavefield
Field
Data Data PreparationData PreparationData PreparationData Preparation
Data Edit
Erroneous Erroneous Erroneous Erroneous
breaktimebreaktimebreaktimebreaktime
Hydrophone recordingsHydrophone recordingsHydrophone recordingsHydrophone recordings
(5 shots at same level)(5 shots at same level)(5 shots at same level)(5 shots at same level)
DownholeDownholeDownholeDownhole Geophone Geophone Geophone Geophone
recordingsrecordingsrecordingsrecordings
(5 shots at same level)(5 shots at same level)(5 shots at same level)(5 shots at same level)
StackStackStackStack
ErroneousErroneousErroneousErroneous
transit timetransit timetransit timetransit time
DistortedDistortedDistortedDistorted
waveformwaveformwaveformwaveform
Hydrophone & Geophone shot editing
1 Geophone level
50 M
s50
Ms
50 M
s50
Ms
Tim
eT
ime
Tim
eT
ime
200
Ms
200
Ms
200
Ms
200
Ms
Tim
eT
ime
Tim
eT
ime
� Stacking Techniques
Median Stack
Median Stack
Mean Stack
Raw Shots
The median value The median value The median value The median value
in each sample is selected.in each sample is selected.in each sample is selected.in each sample is selected.
The method only uses an The method only uses an The method only uses an The method only uses an
odd number of shots.odd number of shots.odd number of shots.odd number of shots.
Median Stack Result
Vertical Geophone (Z)
Time
De
pth
� Normalization and TAR
Normalisation & TAR
Vertical Geophone (Z)
Time
De
pth
TAR / BPF Result
Vertical Geophone (Z)
Time
De
pth
De
pth
De
pth
De
pth
De
pth
Frequency (Hz)Frequency (Hz)Frequency (Hz)Frequency (Hz)180180180180 0000
Power SpectrumPower SpectrumPower SpectrumPower Spectrum
Bandpass Filter
Vertical Geophone (Z)
Time
De
pth
Power SpectrumPower SpectrumPower SpectrumPower Spectrum
� Wavefield Separation- Velocity Filtering
Wave Shape
Deconvolution
SRD, BPF, TAR
Normalization
Corridor
Stack
Median
StackData Load
and EditField
Data
WavefieldWavefieldWavefieldWavefield
SeparationSeparationSeparationSeparation
UpgoingUpgoingUpgoingUpgoing
WavefieldWavefieldWavefieldWavefield
DowngoingDowngoingDowngoingDowngoing
WavefieldWavefieldWavefieldWavefield
VSP Processing
Wavefield SeparationVelocity Filtering
The upgoing wavetrain is generated by the complete downgoing wavetrain being reflected
and/or Ps converted at each acoustic reflector
The downgoing wavetrain (direct compressional signal + multiple + downgoing Ps) can be
quite long and reverberatory in character & masks the upgoing wavetrain
UpgoingUpgoingUpgoingUpgoingDowngoingDowngoingDowngoingDowngoing
One Way TimeOne Way TimeOne Way TimeOne Way Time
De
pth
De
pth
De
pth
De
pth
Velocity filtering separates these two signals which have different apparent velocities
across the data array. Velocity filtering is done in 3 main stages
1. Estimate 1. Estimate 1. Estimate 1. Estimate DowngoingDowngoingDowngoingDowngoing EnergyEnergyEnergyEnergy
Subtract transit time to vertically
align all downgoing energy
Apply median filter to enhance
in-phase downgoing energy and
suppress all out of phase energy
Shift each trace back to its
original one-way time
1. Estimate 1. Estimate 1. Estimate 1. Estimate DowngoingDowngoingDowngoingDowngoing EnergyEnergyEnergyEnergy
Subtract transit time to vertically
align all downgoing energy
Apply median filter to enhance
in-phase downgoing energy and
suppress all out of phase energy
Shift each trace back to its
original one-way time
One Way TimeOne Way TimeOne Way TimeOne Way Time
De
pth
De
pth
De
pth
De
pth
Estimation of Downgoing Energy
Median Stack TracesMedian Stack TracesMedian Stack TracesMedian Stack Traces
Aligned to First Aligned to First Aligned to First Aligned to First
BreakBreakBreakBreak
Upgoing W
avefie
ld
Upgoing W
avefie
ld
Upgoing W
avefie
ld
Upgoing W
avefie
ld
Estimation of Downgoing Energy
Vertical
Geophone (Z)
Aligned EnhancedAligned EnhancedAligned EnhancedAligned Enhanced
DowngoingDowngoingDowngoingDowngoing
WavefieldWavefieldWavefieldWavefield
Time
De
pth
Do
wn
go
ing
Do
wn
go
ing
Do
wn
go
ing
Do
wn
go
ing
Wa
ve
fie
ldW
av
efi
eld
Wa
ve
fie
ldW
av
efi
eld
Subtraction of Downgoing Energy
UpgoingUpgoingUpgoingUpgoingDowngoingDowngoingDowngoingDowngoing
One Way TimeOne Way TimeOne Way TimeOne Way Time
De
pth
De
pth
De
pth
De
pth
One Way TimeOne Way TimeOne Way TimeOne Way Time
De
pth
De
pth
De
pth
De
pth
By subtracting the downgoing energy from the total
wavefield, a residual wavefield is left, which contains
background noise and the desired upgoing wavefield
Enhance Upgoing Energy
UpgoingUpgoingUpgoingUpgoing
One Way TimeOne Way TimeOne Way TimeOne Way Time
De
pth
De
pth
De
pth
De
pth
Add first break
transit time to
vertically align all
upgoing energy at
it’s two-way time
De
pth
Residual WavefieldResidual WavefieldResidual WavefieldResidual Wavefield
after Subtraction of after Subtraction of after Subtraction of after Subtraction of
DowngoingDowngoingDowngoingDowngoing WavefieldWavefieldWavefieldWavefield
Two-Way Time
Up
go
ing
Wa
ve
fie
ldU
pg
oin
g W
av
efi
eld
Up
go
ing
Wa
ve
fie
ldU
pg
oin
g W
av
efi
eld Add TT - Median Stack
Two Way TimeTwo Way TimeTwo Way TimeTwo Way Time
De
pth
De
pth
De
pth
De
pth
Apply median filter to
enhance in-phase
upgoing energy and
suppress all out of
phase energy
Enhance Upgoing EnergyD
ep
th
Two-Way Time
Enhanced UpgoingEnhanced UpgoingEnhanced UpgoingEnhanced Upgoing
WavefieldWavefieldWavefieldWavefield
Velocity Filtering - Recap
Depth
Time
Depth
Time
Depth
Time
Velocity Filter - Step 1
Depth
Time
Depth
Time
Depth
Time
Velocity Filter: Step 2
� Waveshape Deconvolution
Wavefield
Separation
SRD, BPF, TAR
Normalization
Corridor
Stack
Median
StackData Load
and EditField
Data
Wave ShapeWave ShapeWave ShapeWave Shape
DeconvolutionDeconvolutionDeconvolutionDeconvolution
UpgoingUpgoingUpgoingUpgoing
WavefieldWavefieldWavefieldWavefield
DowngoingDowngoingDowngoingDowngoing
WavefieldWavefieldWavefieldWavefield
VSP Processing
Deconvolution
The function of deconvolution is to precisely improve the
resolution capabilities of the upgoing wavetrain:
It removes the near surface multiples & the bubble effects
It optimizes the resolution characteristics of the source
signature
Deconvolution filters are computed on the downgoing
wavetrain and applied to both the downgoing and upgoing
waves
Wave Shaping Deconvolution on
downgoing wavefield
De
pth
De
pth
TimeTime
yn = fmxn- mm
Time Domain Convolution
MultiplicationFrequency DomainY(w) = F(w) X(w)
Input xnDesired Output ynFilter fm
F(w) =Y(w)X(w)
∑∑∑∑
Depth
Time
Depth
TimeDepth
Time
Depth
Time TWTTWTTWTTWT
Deconvolution
Upgoing WavefieldUpgoing WavefieldUpgoing WavefieldUpgoing Wavefield
after Wave Shaping after Wave Shaping after Wave Shaping after Wave Shaping
DeconvolutionDeconvolutionDeconvolutionDeconvolution
Two-Way Time
De
pth
De
pth
Two-Way Time
UpgoingUpgoingUpgoingUpgoing
WavefieldWavefieldWavefieldWavefield
Wave Shaping Deconvolution on upgoing
wavefield
� Corridor Stack
Wavefield
Separation
Wave Shape
Deconvolution
SRD, BPF, TAR
Normalization
Median
StackData Load
and Edit
Upgoing
Wavefield
Downgoing
Wavefield
Field
Data
CorridorCorridorCorridorCorridor
StackStackStackStack
VSP Processing
Corridor Stack
Corridor
Primary Reflector
Upgoing Multiple
De
pth
Time
The corridor stack is used to:
(1) enhance signal close to the well
(2) eliminate possible residual weak
upgoing multiples in the final VSP data
This data is what is correlated to the
surface seismic.
Corridor Stack
De
pth
Two-Way Time
EnhancedEnhancedEnhancedEnhanced
ZeroZeroZeroZero----PhasePhasePhasePhase
UpgoingUpgoingUpgoingUpgoing
WavefieldWavefieldWavefieldWavefield
Corridor Corridor Corridor Corridor
StackStackStackStack
Corridor StackD
ep
th
Two-Way Time
100ms
(1) enhance signal close to the well(1) enhance signal close to the well(1) enhance signal close to the well(1) enhance signal close to the well
(2) eliminate remaining (2) eliminate remaining (2) eliminate remaining (2) eliminate remaining upgoingupgoingupgoingupgoing
multiples in the final VSP datamultiples in the final VSP datamultiples in the final VSP datamultiples in the final VSP data
Review of Zero Offset VSP Processing� Simple
� Assumptions
– Zero offset source
– Flat layering
– Vertical ray path
– 1D problem
– Use only vertical component
– No shear wave
� Deadline end Dec – effectively end Nov
� ACTIONS
– Unlikely to benefit from 3C processing
– Normalize to event at 0.45 s ?
– Synthetics to model change in the coal
– Event registration prior to subtract
– Composite plots of corridors and synthetics
� ACTIONS OVSP
– Event registration prior to subtraction
– Focus on 349 deg offset – full 3 C processing (output Sv and Sh)
� Vp/Vs picking before and after
� Bandwidth before and after – match bandwidth (amp and phase of wavelet)
– AVO synthetic at reservoir modeling, pressure and pore pressure effects
Offset VSP
Surface SeismicSurface SeismicSurface SeismicSurface Seismic
CorrelationCorrelationCorrelationCorrelation
Surface SeismicSurface SeismicSurface SeismicSurface Seismic
CorrelationCorrelationCorrelationCorrelation
Fault and DipFault and DipFault and DipFault and Dip
IdentificationIdentificationIdentificationIdentification
Fault and DipFault and DipFault and DipFault and Dip
IdentificationIdentificationIdentificationIdentification
CompressionalCompressionalCompressionalCompressional & & & &
Shear Shear Shear Shear imagingimagingimagingimaging
CompressionalCompressionalCompressionalCompressional & & & &
Shear Shear Shear Shear imagingimagingimagingimaging
Surface SeismicSurface SeismicSurface SeismicSurface Seismic
Survey DesignSurvey DesignSurvey DesignSurvey Design
Surface SeismicSurface SeismicSurface SeismicSurface Seismic
Survey DesignSurvey DesignSurvey DesignSurvey Design
VSPVSPVSPVSPVSPVSPVSPVSP
Ps Ps Ps Ps Ps Ps Ps Ps ImageImageImageImageImageImageImageImage
Surface Surface Surface Surface Surface Surface Surface Surface
SeismicSeismicSeismicSeismicSeismicSeismicSeismicSeismic
De
pth
(m
)
Time (s)
Source
Ge
op
ho
ne
s
Depth Model
CompressionalCompressionalCompressionalCompressional & & & &
Shear Shear Shear Shear velocityvelocityvelocityvelocity
CompressionalCompressionalCompressionalCompressional & & & &
Shear Shear Shear Shear velocityvelocityvelocityvelocity
OFFSETOFFSETOFFSETOFFSET
Pp
Ps
Offset VSP Data Processing
� Oblique ray path
� Shear waves contamination
– Noise ?
– or, Additional Information
– Both Sv and Sh!
� No more 1D problem
– 3D or 2D ?
� Need to use 3 axis data
– Need different data processing procedure
Offset VSP
Offset VSP Processing
� Can we treat it as 2D problem?
– Yes, if layering is flat, or
– dipping, but the strike is perpendicular to offset line
� How to treat 2 horizontal components?
– Tool rotates at different levels
– Orientation is unknown, usually
– Need to rotate them
Offset VSP Data - Raw Stack
ZZ XX YY
Review of Simple Offset VSP Processing
Z raw
stack
Z raw
stack
DownDown
Wavefield
Separation
Wavefield
Separation
UpUp
DeconvolutionDeconvolution
UpUp
Velocity
model
Velocity
model
NMO
correction
NMO
correction
VSPCDP
section
VSPCDP
section
CDP Mapping- Final Product OVSP
Tw
o-Way T
ime
DepthOffset
Offset VSP Data - Raw Stack
ZZ XX YY
Event Identifications
ZZ XX YY
Horizontal Rotation
Direct P wave
Crossplot of particle potion
- Hodogram -
X
Y
HMX and HMN
� HMX
– Parallel to horizontal particle motion of the first P wave arrival
– HMX wavefield contains P and SV waves
– They travel in the vertical plan defined by the source and the geophone
� HMN
– HMN contains the horizontal particle motion perpendicular to this plane, SH waves
Wavefield Separation
� Goal
– Separate downgoing and upgoing P and S wave from Z and HMX wavefield, that contain P and SV waves
� Methodology
– Model-based separation
– Wave equation method
– Parametric inversion
Parametric Inversion
� Parametric Model
– Local vector wavefields consist of superposition of plane P and SV waves (down- and up- going)
– Parameters
� P- and S- Velocity, Incident angles of each wave
� Algorithm
– Estimate these parameters by minimizing errors between model andobserved data by non-linear least squares estimation
Wavefield Separation - Offset VSP
“P” Wave Upgoing “P” Wave Downgoing
“S” Wave Upgoing “S” Wave Downgoing
One-Way Time One-Way Time
One-Way Time One-Way Time
Dep
th
Dep
th
Dep
th
Dep
th
Results (1/2) - downgoing wavefields
Down-Going P Down-Going S
Comparison
ZZ XX YY
Results (2/2) - Upgoing wavefields
Up-Going SUp-Going P
Another Example of Results
Review of Offset VSP Processing
HMX
raw stack
HMX
raw stack
Y raw
stack
Y raw
stack
X raw
stack
X raw
stack
Horizontal
Rotation
Horizontal
Rotation
Z raw
stack
Z raw
stack
Down PDown P
Wavefield
Separation
Wavefield
Separation
Up SUp S
Up PUp P Down SDown S
DeconvolutionDeconvolution
Up PUp P
Velocity
model
Velocity
model
MigrationMigration
Migrated
P section
Migrated
P section
