ABSTRACT

To improve the computational efficiency of reverse-time migration (RTM) for vertically transverse isotropic (VTI) media, various acoustic approximations of the elastic wave equations have been presented. Among these, the pseudo-acoustic wave equation, which combines differential and scalar operators, has the advantage that it does not produce shear wave artefacts. In this study, we investigate the feasibility of pseudo-acoustic anisotropic RTM (PA-RTM) for the analysis of synthetic and observed ocean-bottom cable (OBC) datasets of the Volve oil field in the North Sea. To analyse the influence of anisotropic parameters on RTM images and the sensitivity of data components to seismic anisotropy, we perform PA-RTM using synthetic data by incorporating various background models, as well as pressure wavefields and vertical particle acceleration. The synthetic experiments demonstrate that the anisotropic parameter ε plays an important role, whereas δ is negligible in PA-RTM for VTI media, and that vertical particle acceleration is less affected by seismic anisotropy than the pressure wavefields. Our experiments using observed data show that reflectors are better imaged by PA-RTM than by isotropic-RTM, particularly near the reservoir below the strongly anisotropic region, which is supported by angle-domain common image gathers. These results indicate that PA-RTM using only the vertical component is a suitable option for VTI media when insufficient seismic anisotropy data are available.

摘要

为了提高垂直横向各向同性（VTI）介质的逆时偏移（RTM）的计算效率，已提出了弹性波方程的各种声学近似。其中，结合了微分和标量算符的伪声波方程具有不产生剪切波伪像的优点。在这项研究中，我们调查了拟声各向异性RTM（PA-RTM）在北海Volve油田的合成和观测海底电缆（OBC）数据集分析中的可行性。为了分析各向异性参数对RTM图像的影响以及数据分量对地震各向异性的敏感性，我们通过结合各种背景模型以及压力波场和垂直粒子加速度，使用合成数据执行PA-RTM。ε起重要作用，而对于VTI介质，在PA-RTM中δ可以忽略不计，并且垂直各向异性加速度比压力波场受地震各向异性的影响较小。我们使用观察到的数据进行的实验表明，PA-RTM的反射器比各向同性的RTM成像更好，尤其是在强各向异性区域下方的储层附近，这由角域共同图像集支持。这些结果表明，当没有足够的地震各向异性数据时，仅使用垂直分量的PA-RTM是VTI介质的合适选择。