The Prestack Time Migration Study Of Equivalent Offset Method

Seismic method for metallic ore exploration is a new and promising technique. Seismic migration based on significant reflection wave achieved a lot of experience and examples in oil and coal prospecting, but failed to complex geologic structure, faults , attitude of geologic body, steep dip, little size geologic body, ore vein and so on . Therefore it is the main reason that conventional seismic processing made no breakthrough in metallic ore exploration.A prestack time migration is presented that is based on scatter theory, maps prestack data into scatterpoint gathers with two variables(time and equivalent offset) , where the scatter wave events are clear, and images with Kirchhoff prestack time migration. The method is divided into two steps: the first is a gathering process that forms common scatterpoint (csp)gathers;the second is a focusing process that applies a simplified Kirchhoff migration on the csp gathers . A key concept of the method is a reformulation of the double square-root equation (of source-scatterpoint-receiver traveltimes) into a single square root . The single square root uses an equivalent offset that is the surface distance from the scatterpoint to a collocated source and receiver . Input samples are mapped into offset bins of a csp gather, without time shifting , to an offset defined by the equivalent offset . The single square-root reformulation gathers scattered energy to hyperbolicpaths on the appropriate csp gathers.The thesis mainly includes csp gathers forming , influence factors (velocity, dip, step of equivalent offset, showing forms, survey parameters and maximum equivalent offset) on csp gathers, csp gathers characteristics, velocity analysis on csp gathers stacking and results contrast with conventional processing ones. Showing that the method has large offsets , high fold and signal-to-nose , natural antialiasing, accurate velocity analysis in complex structure locations, use of conventional processing tool such as velocity analysis, reducing run time , migration results according with models, provides with a new way to resolve the problems of complex structure and little size geologic body imaging.