含流体弱能量暗点储层的地震识别机理与方法

Dim spot reservoirs, showing quite weak seismic energy, are great potential for future hydrocarbon exploration. However, they are difficult to be recognized due to its deeper buried depth and weak or even disappeared seismic reflection amplitude. Therefore, this project focuses on the seismic recognition mechanisms and methods of fluid-bearing dim spot reservoirs based on the essential characteristics of the frequency-dependent dispersion and attenuation that gas reservoirs inherently exist, and the characteristics are independent on the acoustic impedance contrast between the gas reservoirs and their surrounding rocks. We establish the basic numerical analysis methods to depict the frequency-dependent seismic responses of dim spot reservoirs. These methods to study the seismic identification mechanisms of fluid-bearing dim spot involve the calculation of the frequency-dependent elastic moduli, asymptotic representation of the frequency-dependent seismic reflection and refraction coefficients for multi-layers at multi-incident angles and the diffusive-viscous wave equation-based numerical simulation of pre- and post-stacking seismic data of fluid-bearing dim spot reservoirs. Furthermore, the goal of this project is to present the direct and indirect indicators that are seismic amplitude-independent and more definite in their mechanisms to identify the dim spot reservoirs. The indicators include fluid mobility inversion of dim spot reservoirs based on the frequency-dependent dispersion anomalies in pre-stacking seismic data, the frequency-dependent dispersion & attenuation versus offset (FDAVO) inversion of dim spot reservoirs and multiple types of frequency-dependent seismic-shadow anomalies beneath the dim spot reservoirs

弱能量暗点储层具有很大的勘探潜力，但由于暗点储层通常埋深较大、地震反射振幅弱甚至消失，直接识别十分困难。因此，本项目基于油气储层存在固有的依赖频率的地震频散和衰减的本质特性，而这一特性不依赖油气储层与围岩之间的波阻抗差，探索弱能量暗点储层的地震识别机理与方法。通过建立描述暗点储层依赖频率的地震响应的数值分析基础方法，包括依赖频率的弹性参数计算、多层多角度依赖频率的暗点储层地震反射与透射系数的渐近表示、含流体暗点储层的弥散粘滞波动方程依赖频率的叠前叠后地震响应数值模拟，研究含流体暗点的地震识别机理，进而构建机理更明确的、不直接依赖地震反射振幅的含流体暗点储层的直接和间接识别标志，包括基于叠前地震资料依赖频率的频散异常提取的暗点储层流度反演、随偏移距变化的依赖频率的地震频散衰减（FDAVO）参数反演、含流体暗点储层下部依赖频率的多种“地震伴影异常”识别。

本项目基于油气储层存在固有的依赖频率的地震频散和衰减的本质特性，而这一特性不依赖油气储层与围岩之间的波阻抗差，探索弱能量暗点储层的地震识别机理与方法。主要研究了弱能量暗点储层地震响应的数值模拟与分析、弱能量暗点储层的地震识别方法，达到了预期研究目标和考核指标，取得了一系列研究成果。⑴ 在弱能量暗点储层地震响应的数值模拟与分析方面：建立了孔隙-裂缝型暗点储层地震岩石物理模型与地震响应机理的数值正演方法、基于非均匀弥散-粘度-频散波动方程的多相流体饱和暗点储层岩石依赖频率的地震响应数值模拟方法、多相不混溶流体饱和裂缝-孔隙型深层暗点储层岩石依赖频率的地震响应数值分析方法、含流体孔隙介质依赖频率的AVOA及其与裂缝特征之间关系的数值分析方法，这些工作为研究暗点储层岩石物性和流体特征等多种因素影响下的弹性性质及地震响应机理提供了基础方法，可为实际暗点储层地震检测方法的可行性、适应条件和识别陷阱，指导建立机理更加明确的暗点型油气储层检测方法等提供可靠的依据。⑵ 在弱能量暗点储层的地震识别方法方面：构建了改善深层弱能量暗点储层刻画精度的地震资料低频增强方法、基于叠前地震资料的敏感弹性模量频散异常反演及暗点储层的地层频散阴影检测方法、基于叠前叠后地震资料的储层流体流度反演的暗点储层刻画方法、基于地震资料能量密度反演的暗点储层地震检测方法，为利用含流体暗点储层固有的频散和衰减特性，实现机理更加明确的暗点型油气储层地震检测提供了有效的基础方法和支持。⑶ 上述方法全部形成了具有自主知识产权的软件模块集，已在油气勘探开发中推广应用，实现了科研成果的生产转化。