噪声对叠前深度偏移层速度精度的影响分析

Influence analysis of noise on precision of prestack depth migration interval velocity

本文基于地质模型研究了叠前深度偏移中随机噪声和规则噪声对层速度估计精度的影响。结果表明:随机噪声和规则噪声对层速度估计精度的影响规律一致,其影响呈现阶段性特点,即存在界限信噪比。当信噪比高于界限值时,速度误差较小且趋于稳定,对速度精度影响较小;信噪比低于界限值时,速度误差迅速增加,严重影响速度精度;与同等级别的随机噪声相比,规则噪声产生的影响更严重,规则噪声具有更高的界限信噪比。在此基础上,本文进一步分析了静校正时差对界限信噪比的影响。结果表明:对于随机噪声,1.5倍采样时间的静校正时差就会严重影响层速度的估算精度,从而显著地提高了噪声的界限信噪比。因此在实际地震资料叠前深度偏移处理中,必须进行地震信号一致性处理、叠前噪声衰减,减小静校正时差,只有这样才能提高叠前深度偏移速度模型的精度。

Based on geologic model, the paper studied the influence of random and regular noises on the precision of interval velocity estimation in prestack depth migration. The results showed that the random and regular noises have consistent influence regularity on the precision of interval velocity estimation, which is characteristic of stage, limit signal-to-noise (S/N) ratio. The velocity error is minor, tends to stable and has small influence on the velocity precision when the S/N ratio is greater than limit value; on the contrary, the velocity error increased rapidly and seriously affects the velocity precision when the S/N ratio is inferior to the limit value. In comparison with same level's random noises, the regular noises produce more serious influence and have higher limit S/N ratio. On that bases, the paper further analyzed the influence of static moveout on limit S/N ratio.The results showed that for random noises,the static moveout of 1.5 times of sampling time may seriously affect the estimated precision of interval velocity,which may significantly raise the limit S/N ratio.So,it should carry out seismic signal consistency processing, prestack noise attenuation and reducing static moveout in prestack depth migration processing of practical seismic data, and only doing so may we improve the precision of the prestack depth migration velocity model.