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Published byGerald Hipps Modified over 5 years ago

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Making CMP’s From chapter 16 “Elements of 3D Seismology” by Chris Liner

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Outline Normal Moveout Stacking

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Normal Moveout x T Hyperbola:

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Normal Moveout x T “Overcorrected” Normal Moveout is too large Chosen velocity for NMO is too (a) large (b) small

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Normal Moveout x T “Overcorrected” Normal Moveout is too large Chosen velocity for NMO is too small (a) large (b) small

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Normal Moveout x T “Under corrected” Normal Moveout is too small Chosen velocity for NMO is (a) too large (b) too small

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Normal Moveout x T “Under corrected” Normal Moveout is too small Chosen velocity for NMO is too large (a) too large (b) too small

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Vinterval from Vrms Dix, 1955

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Vrms V1 V2 V3 Vrms < Vinterval

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Vinterval from Vrms

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Primary seismic events x T

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x T

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x T

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x T

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Multiples and Primaries x T M1 M2

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Conventional NMO before stacking x T NMO correction V=V(depth) e.g., V=mz + B M1 M2 “Properly corrected” Normal Moveout is just right Chosen velocity for NMO is correct

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Over-correction (e.g. 80% Vnmo) x T NMO correction V=V(depth) e.g., V=0.8(mz + B) M1 M2 x T M1 M2

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f-k filtering before stacking (Ryu) x T NMO correction V=V(depth) e.g., V=0.8(mz + B) M1 M2 x T

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Correct back to 100% NMO x T NMO correction V=V(depth) e.g., V=(mz + B) M1 M2 x T M1 M2

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Outline Convolution and Deconvolution Normal Moveout Stacking

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NMO stretching V1 V2 T0T0 “NMO Stretching”

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NMO stretching V1V1 V2V2 T0T0 “NMO Stretching” V 1 <V 2

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NMO stretching V1V1 V2V2 V 1 <V 2 NMO “stretch” = “linear strain” Linear strain (%) = final length-original length original length X 100 (%)

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NMO stretching V1V1 V2V2 V 1 <V 2 X 100 (%) original length = final length = NMO “stretch” = X 100 (%)

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stretching for T=2s,V1=V2=1500 m/s Green line assumes V1=V2 Blue line is for general case, where V1, V2 can be different and delT0=0.1s (this case: V1=V2) Matlab code

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Stacking + + =

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+ + = Stacking improves S/N ratio

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+ = Semblance Analysis “Semblance” + X Twtt (s)

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+ = Semblance Analysis + X Twtt (s) V3V3 V1V1 V2V2 V Peak energy

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