Seismic Imaging Of Surface-related Multiples

With the development of oil geophysical prospecting, exploration target areas are moreand more complicated. Based on this, we should make fully use of the seismic data in hand toget more valuable and accurate seismic imaging, to provide reliable support for follow-upgeological reservoir description.Based on the above research background, we re-examine the seismic multiples, which areusually regarded as noise because of its negative effect in conventional primary imaging.There’s no absolute criterion to distinguish signal and noise. The criterion may change withthe varying target or with the developing technology.In fact, seismic multiples propagation is similar as primaries. Multiples propagate morethan one round journey between the reflection interfaces, so seismic multiples also containvaluable geological structure information in them. Multiples have longer propagation paths,with wider covering area. Besides, multiples have smaller reflection angle, so in somecomplex geological area, multiples contain seismic information which we could not get fromprimaries. So we could get more valuable seismic exploration information by utilizeingmultiples as signal rather than noise.The paper proposed two kinds of methods to get surface-related multiples imaging. Forthe first method, we transformed surface-related multiples into pseudo-primares and then didthe migration of pseudo-primares. For the other method, we studied the generalized one-wayequation shot profile migration for joint imging of primaries and surface-related multiples.The paper used cross-correlation and stack technique to make pseudo-primary from surface-related multiples, and then employed a linear transform of local slant stack to improvesignal-to-noise ratio. Next, the paper studied three ways of pseudo-primaries applications.Firstly, the paper did migration of pseudo-primaries to get surface-related multiples imaging;Secondly, the paper proposed using the pseudo-primaries imaging for complementing the lackof seismic primary imaging due to acquisition system break because of obstacle topography;Last but not least, the paper presented applying a Least-squares Matching Filter (LMF) andRMS amplitude correction method to do pseudo-primaries correction, to fill the conventionalmissing seisimic data because of the limit of acquisition system. Tests on numerical modeland field data showed the methods are workable and effective.The paper also proposed generalized shot profile migration for joint imaging ofprimaries and surface-related multiples. This method replaces the impulsive source waveletwith the sum of impulsive source wavelet and recorded data containing both primaries andmultiples and uses data containing both primaries and multiples as the input data instead ofprimary reflections. In the migration process, data containing both primaries and multiplesrecorded on the surface are extrapolated backward to each depth level, and the sum ofimpulsive source wavelet and recorded data containing both primaries and multiples areextrapolated forward to the same depth levels, followed by a2D deconvolution imagingcondition which could suppress the crosstalk artifacts generated by interference of upgoingand downgoing events not associated with the same subsurface reflection points. Tests onnumerical model and real data showed that, the method could not only get the correct imagingusing both primaries and surface-related multiples but also achieve a wider coveragecompared with conventional migration of using only primary reflections.