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SOURCE LOCALIZATION BY SOURCE LOCALIZATION BY DIFFRACTION STACKINGDIFFRACTION STACKING
Denis AnikievDenis Anikiev
St.Petersburg State UniversitySt.Petersburg State University
Localization of seismic eventsLocalization of seismic events
Hydraulic fracturingHydraulic fracturing
Localization in seismologyLocalization in seismology
Localization of casing leak at deep Localization of casing leak at deep boreholesboreholes
Prediction of oilPrediction of oil--andand--gas presence in gas presence in reservoirreservoir
Input: Input: Recorded SeismogramRecorded Seismogram
MethodologyMethodology
W (TW (Tii
,x,z) = ,x,z) = ∑∑
u[u[ξξkk
, , ττ((ξξkk
,x,z) ,x,z) ––
TTii
]]kk
Discretize subsurfaceDiscretize subsurface
Fix image point Fix image point (x,z)(x,z)Compute traveltimes Compute traveltimes ττ((ξξkk,,x,z)x,z) for all receivers for all receivers ((ξξkk, , z=0)z=0)Diffraction stack:Diffraction stack:
Z
XX
TT
SOURCESOURCE
Stacking procedureStacking procedure
Z
X
T
SOURCESOURCE
Stacking procedureStacking procedure
Z
X
T
SOURCESOURCE
Stacking procedureStacking procedure
Z
X
T
SOURCESOURCE
Stacking procedureStacking procedure
Z
X
T
SOURCESOURCE
Stacking procedureStacking procedure
Z
X
T
SOURCESOURCEWRONG WRONG DEPTHDEPTH
Stacking procedureStacking procedure
Z
X
T
SOURCESOURCEWRONG WRONG DEPTHDEPTH
Stacking procedureStacking procedure
Z
X
T
SOURCESOURCEWRONG WRONG DEPTHDEPTH
Stacking procedureStacking procedure
Z
X
T
SOURCESOURCEWRONG WRONG DEPTHDEPTH
Stacking procedureStacking procedure
Z
X
T
SOURCESOURCEWRONG LATERAL POSITIONWRONG LATERAL POSITION
Stacking procedureStacking procedure
Z
X
T
SOURCESOURCEWRONG LATERAL POSITIONWRONG LATERAL POSITION
Stacking procedureStacking procedure
Z
X
T
SOURCESOURCEWRONG LATERAL POSITIONWRONG LATERAL POSITION
Stacking procedureStacking procedure
Z
X
T
SOURCESOURCEWRONG LATERAL POSITIONWRONG LATERAL POSITION
Stacking procedureStacking procedure
Repeat for all times, square and sum Repeat for all times, square and sum Image Function:Image Function:
Input: Input: Recorded SeismogramRecorded Seismogram
MethodologyMethodology
W (TW (Tii
,x,z) = ,x,z) = ∑∑
u[u[ξξkk
, , ττ((ξξkk
,x,z) ,x,z) ––
TTii
]]kk
IM (x,z) = IM (x,z) = ∑∑
W (TW (Tii
,x,z), T,x,z), Tii
[t[t11
,t,t22
]]22
ii
∩∩
max( IM (x,z) ) = IM (xmax( IM (x,z) ) = IM (x00
,z,z00
))x,zx,z
Discretize subsurfaceDiscretize subsurface
Fix image point Fix image point (x,z)(x,z)Compute traveltimes Compute traveltimes ττ((ξξkk,,x,z)x,z) for all receivers for all receivers ((ξξkk, , z=0)z=0)Diffraction stack:Diffraction stack:
Point of maximum Point of maximum corresponds to real source position corresponds to real source position (x(x00,z,z00)) ::
Representation of localization resultRepresentation of localization result
Image function plotImage function plot
Model of homogeneous mediumModel of homogeneous medium00 12001200
20002000 Point seismic Point seismic source locationsource location
Set of 198 receiversSet of 198 receivers
HOMOGENEOUS MEDIUMHOMOGENEOUS MEDIUM
XX
ZZ
Subsurface grid step Subsurface grid step 22 mm
10m interval10m interval
SCHEMESCHEMEMedium velocity 3000 m/sMedium velocity 3000 m/s
Seismogram in case of homogeneous mediumSeismogram in case of homogeneous medium
Result of localization for homogeneous mediumResult of localization for homogeneous medium
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itrar
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its
Surface vs. borehole observationsSurface vs. borehole observations
Surface arraySurface array Borehole arrayBorehole array
+ Large acquisition+ Large acquisition
+ Good illumination+ Good illumination-- Near surface complexityNear surface complexity
-- Surface noiseSurface noise
-- Big distance from targetBig distance from target
BUT:BUT:
Seismogram with synthetic noise.Seismogram with synthetic noise. S/N = 0.5S/N = 0.5
Result of localization for data with noiseResult of localization for data with noise.. S/N=0.5S/N=0.5
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0
250
500
dept
h [m
]
250 500 750 1000 1250distance [m]
l_corr = 50 m
Correlation length is Correlation length is 5050 mm
Set of 143 receiversSet of 143 receivers
Medium velocity 2000 m/sMedium velocity 2000 m/s
400
360
Point seismic sourcePoint seismic source
Scattering surface layerScattering surface layer
150
Homogeneous mediumHomogeneous medium
Model with scattering overburdenModel with scattering overburden
overburdenoverburden
Seismogram for model with complexitySeismogram for model with complexity
l = 50 ml = 50 m
Result of localization for model with complexityResult of localization for model with complexity
l = 50 ml = 50 m
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Result of localization for model with complexityResult of localization for model with complexity
l = 10 ml = 10 m
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Result of localization for homogeneous modelResult of localization for homogeneous model
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Unknown velocityUnknown velocity
Stack resultsStack results
Consider range of velocitiesConsider range of velocities
Compute image function for each velocityCompute image function for each velocity
Result of localization: V=1800 m/sResult of localization: V=1800 m/s
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Result of localization: V=1880 m/sResult of localization: V=1880 m/s
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Result of localization: V=1960 m/sResult of localization: V=1960 m/s
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Result of localization: V=2040 m/sResult of localization: V=2040 m/s
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Result of localization: V=2120 m/sResult of localization: V=2120 m/s
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Result of localization: V=2200 m/sResult of localization: V=2200 m/s
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Result of stacking over velocityResult of stacking over velocity
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Result of localization: Result of localization: V=2000 m/sV=2000 m/s
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ConclusionsConclusions
Localization by stackingLocalization by stacking
No picking of eventsNo picking of events
Works for poor S/NWorks for poor S/N
Not harmed by surface complexityNot harmed by surface complexity
Localization without knowledge of precise Localization without knowledge of precise velocity modelvelocity model
OutlookOutlook
• AApplicapplicationtion to the real datato the real data
•• TThe extension to 3he extension to 3--D mediaD media
• AApplicapplicationtion to synthetic models with to synthetic models with gradient velocity variationsgradient velocity variations
• Real time monitoring systemReal time monitoring system
Partial support by Partial support by St.Petersburg University, Institute of St.Petersburg University, Institute of Geophysics of Hamburg Geophysics of Hamburg University, the WaveUniversity, the WaveInversion Technology (WIT) consortiumInversion Technology (WIT) consortium,, thethe
German Academic Exchange Service (DAAD)German Academic Exchange Service (DAAD) and Shell and Shell CompanyCompany
AcknowledgmentsAcknowledgments
Thank you for attentionThank you for attention