Review of the Green’s Theorem deghosting method Jingfeng Zhang and Arthur B. Weglein M-OSRP 2006 Annual Meeting, June 5 ~ June 7, 2007
Key points Scattered field can be deghosted without source wavelet and vertical derivative of the wavefield Field data test requirements: interpolation and extrapolation, high computation power Derivation of the Green’s theorem deghosting, wavelet estimation and field prediction algorithms
Motivation Remove the seismic distortion due to ghosts Angle and frequency dependent distortion, ghost notch A pre-requisite for all of the current inverse scattering series related algorithms: FSMR, IMA, Imaging and inversion
Green’s Theorem Green’s function =
Configuration for actual wavefield
Deghosting algorithm 2 1 = + 1 2 + 3 3 1 2 = Weglein et al. (2002)
Wavelet estimation algorithm is the image of with respect to the free surface V
Wavelet estimation algorithm 2 3 + = Weglein and Secrest, (1990) V = 1 + 2 3 1 3 2 2 3
Field prediction algorithm
Field prediction algorithm
Deghosting algorithm F.S. Pseudo-M.S. M.S. Earth
Deghosting algorithm F.S. Pseudo-M.S. M.S. Earth
Towed streamer deghosting (Numerical tests) F.S. (0,2) 6.0m M.S. 300m c1=1500m/s c2=2250m/s
With source wavelet Red solid: Exact; Blue dash: deghosting result
FSMR results (point receiver data) Primary At (0,2.5) 1st order FSM 2nd order FSM Using the 1st term in the ISS FSMR series
FSMR results (point receiver data) 1st order FSM Using the 1st term in the ISS FSMR series
Without source wavelet Consequences: (1) Direct wave and its ghost: remains (2) Scattered field: no effect
Without source wavelet Between FS and MS, the scattered field satisfies: Notice there is no source term. From similar derivation of the field prediction: compared to So (1) the absent of source wavelet has no effect on the prediction of the scattered field. (2) the term only contribute to the prediction of the direct wave and its ghost.
Without source wavelet Absent of source wavelet only cause inaccuracy in prediction of the direct wave and its ghost, while the scattered field prediction is accurate Scattered field can be deghosted well even without source wavelet Problems exist at places (especially for shallow water cases) where the direct wave interfere with the scattered field
Field data tests Surface integration: Source wavelet Receiver array Surface data measurements: data interpolation and extrapolation Large computation power Source wavelet Receiver array
Conclusions Green’s theorem deghosting produce encouraging results when the source wavelet is available. Even without the source wavelet, scattered field can still be deghosted. The surface integration requires surface data measurements and high computation power. At the same time, it provides stable results due to that integration. Interpolation and Extrapolation, high computation power are necessary for field data tests.
Acknowledgements M-OSRP sponsors and colleagues