基于吸收衰减补偿的多分量高斯束逆时偏移

高斯束逆时偏移结合了射线类偏移的高计算效率和波动方程逆时偏移的高精度,能很好地处理焦散点、大倾角成像问题,并且具有面向目标成像的能力.多分量地震资料的偏移技术可以对地下复杂构造进行更准确的成像,由于实际地下介质具有黏滞性,研究黏弹性叠前逆时偏移具有一定的现实意义.本文采用高斯束逆时偏移方法对多分量地震数据进行吸收衰减补偿,首先分别给出纵波和转换波共炮域高斯束叠前逆时偏移方法原理,在此基础上推导补偿吸收衰减的表达式,校正Q引起的振幅衰减和相位畸变,实现基于吸收衰减补偿的多分量高斯束叠前逆时偏移.数值模型的测试结果显示,在考虑地下介质的黏滞性时,本文方法具有更高的成像分辨率.

Multiple-component Gaussian beam reverse-time migration based on attenuation compensation

Anelastic properties of subsurface media can cause amplitude loss and phase distortion of seismic waves,especially in high-attenuation areas such as the gas chimneys as observed in several oil and gas fields.In migration of such data sets,we usually obtain poor seismic images of the structure within and below high-attenuation gas-filled reservoirs.To improve the resolution of the migration image,we must deal with these attenuation effects. Multiple-component seismic data contains both PP and PS waves. The PS-wave image complements the traditional PP-wave image,resulting in a more accurate subsurface characterization.Reverse-time migration of multiple-component seismic data can improve the accuracy of imaging subsurface complex geological structures. While viscoelastic prestack reverse-time migration is of practical significance because it considers the viscosity of subsurface media.As a new migration tool,Gaussian beam reverse-time migration (GBRTM) combines the high efficiency and flexibility of Gaussian beam migration with the high accuracy of wave equation reverse-time migration,which can overcome the problems of caustics,handle all arrivals,yield good images of steep flanks,and is easy to extend to target-oriented implementation.However,GBRTM studies have focused on acoustic waves, and multiple-component GBRTM has been little investigated.Besides,it is not clear how the method should be applied for multiple-component seismic data recorded in attenuating media.Therefore,we propose a multiple-component GBRTM to perform seismic data compensation for frequency-dependent absorption and dispersion.We separate multiple-component seismic data into PP- and PS-waves,and migrate by scalar migration methods.The purpose is to provide a new effective method for multiple-component seismic data migration imaging and to compensate the attenuation simultaneously.First,we derive a common-shot gathers GBRTM algorithm of PP and PS waves.Then,the expressions of attenuation equation and the precision analysis of Green function based on Gaussian beams are developed. Finally we present the principle and procedures of compensation,and then propose an attenuation-compensated multiple-component GBRTM. The migration results of PP and PS waves illustrate that the new method is effective in compensating the amplitude loss and phase shift caused by the anelastic properties of rocks in the field.The migration results have higher amplitudes and more continuous reflectors,especially in deep sections.Comparison of single trace waveforms extracted from migration results shows that the proposed approach effectively compensates the absorption of the subsurface medium.From the amplitude spectra and power spectra,we see the new method effectively compensates the seismic wave energy,and especially enhances the energy of the middle- and high-frequency components. We propose a attenuation-compensated multiple component method based on GBRTM to compensate the energy and correct the phase in the seismic wave migration.Compared to the Gaussian beam prestack depth migration proposed by Hill,GBRTM is superior in theory because it does not require local slant stack and steepest-descents evaluation.The new attenuation compensation method is an attractive migration algorithm,because it not only has the advantages of the high computational efficiency of ray-based Q-compensated migration,but also retains the high accuracy of the attenuation compensation method based on wave equation reverse-time migration.We have also demonstrated that the images obtained by the new method can compensate the attenuation and dispersion effects.Numerical results further verify that the proposed approach can effectively improve the resolution and quality of migrate images for both PP- and PS waves,particularly beneath high-attenuation zones.