source localization by diffraction stacking denis anikiev

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


Z

X

T

SOURCESOURCEWRONG WRONG DEPTHDEPTH


Z

X

T

SOURCESOURCEWRONG LATERAL POSITIONWRONG LATERAL POSITION


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

Arb

itrar

y un

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

Arb

itrar

y un

its

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

Arb

itrar

y un

its

Result of localization for model with complexityResult of localization for model with complexity

l = 10 ml = 10 m

Arb

itrar

y un

its

Result of localization for homogeneous modelResult of localization for homogeneous model

Arb

itrar

y un

its

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

Arb

itrar

y un

its


Arb

itrar

y un

its

Result of stacking over velocityResult of stacking over velocity

Arb

itrar

y un

its

Result of localization: Result of localization: V=2000 m/sV=2000 m/s

Arb

itrar

y un

its

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

source localization by diffraction stacking denis anikiev

Documents