Abstract:Based on ray tracing and wave equation illumination result,the conventional method for improving the imaging quality of the shadow zone of a target layer with complex structures is to analyze the distribution of irradiating energy in the shadow zone and select the infilled shots according to the contribution from illuminated energy to the shadow zone.However,it is impossible to accurately create a geological model due to the complexity of geological structures,which will affect the illumination analysis to complex target layer and lead to it is difficult to improve the imaging quality of the target area with complex structure by infilling shots.Based on this situation,this paper proposes the method for improving the imaging quality of shadow zone of the target layer on the basis of the legacy data according to the local similarity theory:Firstly,the geometry should be drawn up according to the geological task of exploration area,and the shot interval (or shot line interval) should be as small as possible;Secondly,calculate the local similarity of each trace of the common imaging point (CIP) gathers of the legacy seismic data and pick target layer in stacked data;so the local similarity of target layer for all traces of all shots is obtained; Thirdly,use spatial interpolation to calculate the local similarity of all shots and the contribution of the normal shots to the target layer with the designed geometry,and establish the relation curve (curved face) between the local similarity of each CIP gather and spatial position to determine the zones with low local similarity value; Finally, use the uniformity of local similarity of target layer as index to determine the positions and density of infilled shots.The verifications by theoretical data and practical data indicate that this method can economically infill suitable shots and improve the imaging effect of shadow zones of the target layer in areas with high steep dip angle and overthrust structures and whose lateral velocities change severely.
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