time%reversal+acous/cs,+virtual+ source+imaging,+and
TRANSCRIPT
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Time-‐reversal acous/cs, virtual source imaging, and seismic
interferometry
Haijiang Zhang
University of Science and Technology of China
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Time-‐reversal acous/cs
Fink, 1997
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Time-‐reversal and super resolu/on
More heterogeneous and scaEered the medium between the source and the TRM, the more focused the /me-‐reversed signal.
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Time-‐reversed seismic loca/on
– No picking required
– Automatic (real-time) location
– Using full waveforms
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Virtual source method
Bakulin and Calvert, 2006
Sources Sk on the surface
Receivers in the borehole
The goal is to construct seismic record from virtual source to receivers.
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Synthe/c velocity models
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Virtual source gather (at 900 m) Real source gather (at 900 m)
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Construc/ng virtual source (VS) data
€
Ska (t) = wk (t) ˜ S ka (t)
Bakulin and Calvert, 2006
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Shuster, SEG 09
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China
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? 98 geophones
120 shots
Overburden
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Seismic Interferometry
• Interferometry is a family of techniques in which waves, are superimposed in order to extract informa/on about the waves (from wikipedia).
• Seismic Interferometry involves cross correla/ng and stacking diffusive waves to extract Green’s func/ons.
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Cross-‐correla/on and stacking
Gsa(t): Green’s func/on from source s to a. e(t): Source /me func/on.
Cross-‐correla/on
Stacking: source averaging
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Homogeneous medium
Circular sources
a) τ= -‐3T0 b) τ= -‐T0 c) Τ=10T0
Larose et al., 2005
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Homogeneous medium
800 sources (par/ally covered)
a) τ= -‐3T0 b) τ= -‐T0 c) Τ=10T0
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Heterogeous medium
800 sources (par/ally covered)
a) first-‐part coda b) late coda
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Time-‐reversal interpreta/on of the correla/on process
Treat a as the virtual source
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(Weaver and Lobkis, Ultrasonics, 40, 435-‐439, 2002)
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(Weaver and Lobkis, Ultrasonics, 40, 435-‐439, 2002)
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