部分饱和岩石的粘声波频变各向异性理论研究

本项目旨在提高对含裂隙储层部分饱和岩石粘声波频变各向异性的认识。拟研究：1）建立一种计算双相不混溶流体饱和裂隙粘声波弹性模量的理论模型。在粘声波介质波传播速度基础上，建立考虑频散、吸收衰减的方法与理论，将岩石物理模型得到的品质因子变化关系替换到速度中，构建粘声波频变各向异性介质中同时包含喷射流力学机制和斑块效应的统一波传播模型；2）结合流体的相对运动特性及喷射流和斑块效应耦合影响，推导粘声波频变各向异性反射系数表达式。研究耦合的喷射流和斑块效应及含水饱和度对复杂介质的粘声波和横波各向异性的影响；3）提出一种考虑频变方位角效应的粘声波正演，为贝叶斯反演奠定基础；提出新的部分饱和粘声波频变各向异性贝叶斯反演方法，用于表征裂缝。最后，项目反演理论模型数据和南方某气田三维全方位实际资料，获得高精度、高分辨率的裂缝密度、裂缝走向、裂缝尺度和含水饱和度。为复杂油气藏精细勘探奠定理论基础和提供技术支撑。

Seismic wave propagation through fractured rocks is greatly influenced by the fracture system and fluid content. The purpose of this project is to improve the understanding of frequency-dependent seismic anisotropy of viscoacoustic wave in partially saturated fractured reservoirs. Based on the previous theories, this project intends to research the following three aspects: (1) a theoretical model for calculating the elastic modulus of viscoacoustic waves in two immiscible fluid-saturated fractured rocks are presented. Based on the propagation velocity of seismic wave in viscoacoustic wave medium, the method and theory of dispersion, absorption and attenuation are taken into account to substitute the relationship of the quality factor obtained using the rock physics model into the seismic wave velocity, and the unified wave propagation model of viscoacoustic wave’s frequency-dependent anisotropy with the coupled impact of ‘squirt flow’ and ‘patch saturation’ effects is constructed. (2) The matrix of reflection coefficient of viscoacoustic wave’s frequency-dependent anisotropy including quality factor and fracture parameters are derived in combination with the relative mobility characteristics of fluids and the coupled impact of ‘squirt flow’ and ‘patch saturation’ effects. The response of amplitude versus angle and azimuth (AVAZ) of coupled ‘squirt flow’ and ‘patch saturation’ and water saturation to shear wave splitting and viscoacoustic wave frequency-dependent anisotropy of transverse isotropy (TI) medium, orthogonal medium, monoclinic medium and so on are researched..(3) Based on the theory of coupled ‘squirt flow’ and ‘patch saturation’, a forward modeling of viscoacoustic wave considering frequency-dependent azimuthal effect is proposed, which lays a foundation for Bayesian inversion. In this project, a new Bayesian inversion method of viscoacoustic wave frequency-dependent anisotropy in partially saturated fractured reservoirs is proposed to characterize fractures reliably from seismic reflections data. .Finally, using theoretical model data to verify the effectiveness of the method, the high-precision and high-resolution fracture density, fracture strike, fracture size and water saturation can be estimated using three-dimensional full azimuthal acquisition real field seismic datasets from a gas field in south China. It lays the theoretical foundation and provides the technical support for the fine seismic exploration of complex oil and gas reservoirs.