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Ghost Common Source Point Ray Tracing Dynamic Correction Based on Complex Near-surface Areas in Coalfield

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Tutor: PengSuPing
School: Beijing
Course: Mineral prospecting and exploration
Keywords: coalfield seiemic exploration,complex near surface,ghost common sourcegather,dyn
CLC: P631.4
Type: PhD thesis
Year:  2012
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Abstract:
Topography and weathered layer have a great negative influence on reflection traveltime in the complex near-surface areas. In order to eliminate the effects, we analyze raypath error which is caused by the assumption of ray vertical incidence in near surface under surface-consistent static correction. We also analyze normal moveout correction error and velocity error, because of reflection traveltime deviation from the hyperbolic relationship after datum static correction applied. According to Huygens¡¯principle, Fermat¡¯s principle and Reciprocity principle, we present the concept of ghost common shot point gather (GCSP). And then based on the GCSP gather, we present GCSP ray tracing dynamic correction method. It is an assumption that the ghost source is located in the center of the CMP bin, and traveltime error, caused by the assumption, is analyzed in detail. Finally the feasibility of this method is demonstrated.Considering the actual situation, we focus on three factors to analyze the accuracy of near-surface velocity model inverted by first break traveltime tomography. The factors are source well depth, constraint velocity and ray azimuth. Discussing the way to increase the ray azimuth, such as well-surface simultaneous inversion and split shooting. Two methods are presented to determine the minimum constraint velocity, such as uphole time and auxiliary source. Finally GCSP ray tracing dynamic correction method is tested by real coalfield seismic data, the results shows that the effect of near surface is eliminate effectively and the continuity of coal seam reflection events are enhanced extraordinarily in the stack profile.
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