地震波在非均匀多孔介质分界面上的反射特征及其对储层刻画的启示

An essential feature of subsurface rocks is the universal presence of heterogeneity occurring at various scales. However, the conventional seismic analysis based on the assumption that rocks are purely elastic or homogeneous porous, typically ignores the local viscous fluid flow which is considered to be the dominant cause of elastic wave dispersion and attenuation. We propose to use the theory of effective Biot media which reduce the heterogeneous porous media into an effective homogeneous media, to compute the poroelastic reflection from the diffusive boundary of heterogeneous porous media. The primary objective of this research will focus on: 1) We will systematically study the physical law of seismic reflection and transmission problems as well as the seismic energy distribution in heterogeneous poroelastic media, thereby quantifying the impact of both global flow and local flow simultaneously on the signatures of seismic reflectivity; 2) On the basis of the frequency and angle dependent poroelastic seismic reflection, we will establish a link between the pore pressure relaxation-related seismic attributes and fluid mobility (viscosity and permeability). The results are of prime importance for detailed reservoir characterization and integration of different geophysical measurements at various frequency band.

岩石多尺度的非均质性是地下孔隙介质的最基本表征之一，然而传统的基于纯弹性和均匀孔隙双相介质的地震反射系数并没有考虑到对弹性波频散和衰减起主导作用的“局部流”影响。针对弹性波在非均匀孔隙介质分界面上反射和透射问题在理论上遇到的挑战，申请人提出了利用等效Biot介质理论来解决问题的思路，拟开展以下研究工作：1）基于多孔岩石物理机制，揭示地震波在非均匀多孔介质分界面上的反射和透射物理规律及地震波能量在弥散界面的分配关系，并定量评价局部“中观流”和宏观的Biot流对地震反射特征的影响; (2) 在研究地震反射系数随入射角和频率变化关系的基础上，建立流体流动性能（粘滞度和渗透率）与孔隙压力弛豫相关的地震属性的映射关系。项目的研究成果对非均质储层的精细地震刻画和融合利用跨频段的地球物理数据来描述地球介质多尺度的非均质性都具有重要的意义。

针对地震波在非均匀孔隙介质分界面上的反射特征及其背后物理机理模糊不清的问题，本项目在等效Biot理论框架下推导了物理意义明确的非均匀孔隙介质地震反射系数和透射系数方程，探讨地震反射系数随入射角和频率的变化关系，为揭示复杂非均质含油气储层频变AVO物理本质奠定理论基础。通过研究指出中观尺度的孔隙压力弛豫对非均质储层的AVO特征影响不可忽略，对于典型三类AVO储层来说，可以引起反射振幅最高达40%的频散效应和16度的相位变化；针对不同AVO类型的有衰减特性的储层，定量表征了其对地震波形、相位和振幅能量的影响，系统研究了三种衰减储层的AVAF地震反射特征，并进一步探讨对复杂非均质储层的定量地震解释和地震成像产生影响；建立弥散界面地震反射系数与流体粘滞度、渗透率的定量映射关系，对其物理机制进行了详细探讨，并首次在4D重油衰减型储层的实际数据中给出了流动性能对地震属性影响的证据。项目的相关研究成果发表在勘探地球物理有国际影响力的期刊《JGR-solid earth》,《Geophysics》,《Geophysical Prospecting》.