Study On Diffracting Objective Imaging Methods In Heterogeneous Media

With the development of precision exploration and further exploitation over structureand lithology reservoirs, as a precondition of more precise seismic interpretation, thehigh-resolution imaging of sub-surface media (especially the heterogeneity geological bodies)is playing an increasingly important role in oil and gas field prospecting. At the present stage,seismic interpretation mainly focuses on the object of faults, channels, salt-bodies andcarbonate reservoirs being rich in karsts and cracks. It is the reason why people focus on thispoint that these kinds of objects hold the characteristic of sharp lateral and vertical velocityvariation, relative small scale, strong anisotropy and irregular shape, whose response is shownas complex diffraction on seismic record.However, traditional seismic data processing based on the reflection wave always treatdiffraction wave as noisy, which is different from continuous reflection events. Even thoughdiffraction are focused properly, its low energy will also hardly be recognized in the imagingresult with reflection of strong stack amplitude, which leads to a poor imaging resolution ofanisotropy geological bodies. Therefore, the method of detecting diffraction and accuratelyimaging anisotropy objects against diffraction wave came into being. In this paper, standingon the analysis of diffraction responses between different seismic traces, a high-precisionimaging method was approached, which is applied to migration of anisotropy diffractionobject in order to enhance seismic identification ability and seismic interpretation of complexgeological bodies.This paper emphatically studies diffraction object imaging method in dip angle domain,which main work can be arranged as follows:(1) based on the Gauss-Beam common angleimaging, derivate and achieve CIG-extracted method;(2) design two reflection apex removal dip angle domain filters, which one is based on local dip estimation and the other one is basedon semblance analysis. Both of them can achieve good separation results. By comparison withthe imaging profiles stacked by CIGs in dip angle domain before and after wavefieldseparation, numerical tests demonstrate that this dip angled domain method improves imagingresolution of heterogeneous body;(3) according to sensitivity of diffraction wave on CIGsin dip angle domain, generally achieve diffraction migration velocity analysis, which canfuther improve migration velocity precison;(4) establish diffraction object imaging methodson CIG respectively adapted to complex surface condition and sub-surface elastic wave mediawhich have been proved to be adaptive by model and real data tests.Based on geometry difference between reflection and diffraction on plane wave record,further study and develop diffraction separation methods based on plane wave destructiontechnique. First, realize wavefield separation with plane wave destruction filtering; then, useplane wave prediction to abstract diffraction aim at solving the event phase rotation problemcaused by derivation operator in plane wave destruction. Both of these separation methodscan be proved to be correct by numerical tests. Use one-way wave equation migration methodwith high precision to image diffraction shot records, wich can enhance diffracted objectiveimaging resolution.The paper presents a preserved amplitude prestack depth migration method based on2Ddeconvolution, which not only enhances the imaging energy of weak imaging areas where thefolds are not full but also improves the imaging quality of deep target layers.