页岩储层地震各向异性响应特征研究及应用

Shale represents the strongest seismic anisotropy amongst all rock types, which is also the most significant seismic response of shale gas. Therefore, the research of seismic anisotropic response of shales and its application is extremely important in the development of shale gas exploration. In this project, we study the origin of shale seismic anisotropy, the estimation and analysis of anisotropy, as well as how seismic anisotropy can help in shale gas exploration. For this, we first study the shale core sample and log data, in order to establish accurate anisotropic rock physics models of shale gas reservoir; secondly, we develop anisotropic algorithms for processing and inversion of multicomponent seismic data for shale gas exploration, including seismic velocity analysis, anisotropy parameters estimation and joint inversion of multicomonent seismic. Finally, due to the extremely low porosity and low permeability, we argue that the shale microstructure, such as pore aspect ratio may be more sensitive to seismic properties compared with porosity and permeability, or TOC (Total organic carbon). We propose the concept of mineralogy substitution instead of fluid substitution, and develop techniques to predict the clay content, the distribution of brittle minerals, the volume of organic matters and the lamination of pores and cracks. Microseismic data are also utilized with anisotropy taken into account to help the optimization of hydraulic fractures. This research deals with the critical problem of shale gas seismic exploration in the presence of strong anisotropy, providing both theoretical and technical support for the characterization of ‘sweet spot’ in shale gas, and for the optimization of the hydraulic fracturing of organic shales.

页岩气储层最显著的地震响应特征是速度各向异性；页岩的地震各向异性是所有岩石中最强的。研究页岩的地震各向异性响应特征及其应用是进一步发展页岩气地震勘探技术的关键。本项目将在页岩地震各向异性的成因、分析方法和应用途径等三方面开展研究。首先，从分析页岩岩心及测井数据入手，建立精确的页岩储层地震各向异性岩石物理模型，并针对页岩储层诸如有机质、泥质、脆性矿物质分布、孔隙及裂缝纵横比等特性开展地震响应特征研究及敏感参数分析。第二，探索页岩气探区地震资料的各向异性处理与反演方法，包括速度分析、参数估算及纵横波联合反演等。第三，根据页岩超低孔低渗等特点，提出孔隙结构描述、矿物组分替换等新概念，重点研究泥质含量、脆性矿物质、有机质及孔隙和裂缝排列、纵横比等的预测方法，并结合微地震资料，利用地震各向异性优化压裂参数。总之，通过本项目的研究，为利用地震各向异性进行页岩气甜点检测及储层改造提供理论依据和技术支持。

本项目是针对页岩气储层的地震各向异性开展的理论和方法研究。本项目主要完成了以下三部分的研究：页岩地震各向异性响应机理分析；页岩气储层地震各向异性处理与反演方法研究；页岩气储层地震各向异性应用技术研究。通过四年的攻关在理论方面形成的重要创新性成果包括：明确了页岩储层孔隙度、纵横比、矿物组分、有机质含量等与地震各向异性参数的经验关系；建立了可随地质约束条件的变化不断完善的岩石物理模型；明确了页岩物性参数的地震响应敏感属性。在方法研究方面形成的成果包括：基于VTI介质两参数转换波动校公式的处理新方法；射线参数域地震多波联合反演；基于统计岩石物理的脆性和有机质含量定量预测方法；微地震正演与反演方法；页岩储层构造应力场反演方法。随着研究任务的完成，本项目形成了包括SCI期刊论文、国际会议论文、专利等丰硕的研究成果。理论研究成果对页岩岩石物理研究进展起到了重要的推动作用，方法研究成果已初步应用于我国多个页岩示范区，为页岩地震勘探和工程监测技术的发展提供了重要的技术支持。