面向煤层气储层的裂隙参数AVOA反演方法研究

The Amplitude versus Offset and Azimuth (AVOA) inversion serves as a mainstream solution for fracture evaluation of conventional oil and gas reservoirs cannot be directly applied in the coal-bed methane (CBM) reservoirs. Mostly because there are essential differences for both reservoirs in thickness, pore and fracture structure and fluid properties. Therefore, the theoretical model and inversion equation cannot be used co-applicably. In this project, we will take a representative block in the Qinshui Basin as the research object to build an equivalent medium model to drive the fracture parameters AVOA inversion of the target CBM reservoir. The research can be carried out from three aspects. Firstly, we should solve the equivalent calculation problems of adsorbed gas and dual-porosity system in CBM reservoir, and establish an equivalent medium model which can accurately characterize the composition and structure of CBM reservoir. Then, we prefer to reveal the seismic response mechanism of fracture parameters in CBM reservoir through numerical calculation and seismic forward simulation. Finally, the AVOA inversion equation for CBM reservoir can be constructed by deriving the analytic equation of p-p wave reflection coefficient. Additionally, the stepwise fitting and t-distribution hypothesis test will be used to optimize and constrain the inversion. Consequently, the successful completion of this project can not only form a seismic AVOA inversion technology system for CBM reservoirs, but also provide a key parameter support for the sweet spot accurate identification of CBM reservoir permeability.

地震AVOA反演作为常规油气储层裂隙评价的主流解决方案，尚不能直接应用于煤层气储层，根本原因在于两类储层在层厚、孔裂隙结构和流体性质等方面存在本质差异，理论模型与反演方程无法通用。为此，项目拟以沁水盆地的代表性煤层气区块为研究对象，以构建等效介质模型驱动实现煤层气储层的裂隙参数AVOA反演为研究主线，依次从三方面展开研究：一是解决煤层气储层特有的吸附气和双重孔裂隙系统的等效计算问题，建立能准确表征煤层气储层组成与结构特征的等效介质模型；二是通过模型的正演数值计算与地震波场模拟，揭示煤层气储层裂隙参数的地震响应机制；三是推导适用于煤层气储层的P-P波反射系数解析关系式，构建煤层气储层的AVOA反演方程，采用分步拟合策略和t-分布假设检验方法优化并约束反演。该项目的顺利完成，将形成面向煤层气储层的地震AVOA反演技术体系，进而为煤层气储层渗透性“甜点区”的精准识别提供关键参数支撑。

面向煤层气储层裂缝参数预测的迫切需求，针对常规油气储层裂隙评价的主流解决方案—地震AVOA反演在煤层气储层中的适用与优化问题。项目选取代表性的煤层气区块，通过构建煤层气储层等效介质模型驱动实现储层的裂隙参数AVOA反演，依次开展了三个方面研究：一是利用自相容近似模型和Mori-Tanaka模型解决了煤层气储层吸附气和双重孔裂隙系统的等效计算问题，建立能准确表征煤层气储层组成与结构特征的等效介质模型；二是通过模型的正演数值计算，分析并揭示煤层气储层裂隙参数的地震参数、AVOA响应规律和特征；三是基于Ruger公式推导了煤层气储层的P-P波反射系数解析关系式，构建面向煤层气储层的AVOA反演方程，采用两步拟合反演策略求解获取煤层气储层裂缝参数结果。项目开展了上述三方面内容的研究工作，初步完成了煤层气储层等效介质模型构建，以及驱动实现了储层裂隙参数的地震AVOA反演，研究成果将为煤层气储层渗透性“甜点区”的精准识别提供支撑。