富有机质页岩微-纳米孔隙结构及其对页岩气赋存的控制机理

Shale gas, as a kind of high potential unconventional resource, has attracted much attention around the world. However, two obstacles exist in shale gas exploration and exploitation theory including insufficient understanding about micrometer-to nanometer-scale pore structure and lack mechanics of gas occurrence. In this project, black marine shales from Sichuan Basin are studied to discuss the control mechanism of micrometer-to nanometer-scale pore structure on shale gas occurrence. To begin with, rock physical and geochemistry experiments are carried out to describe the microscopic structure characteristic of shales. Both indirect measurements and direct observations are applied to quantitatively study the multi-scale pore structure of shales. After this, high pressure high temperature gas adsorption experiments are conducted to investigate the controls on methane adsorption capacity of shales, and supercritical methane adsorption behaviors on shales are also discussed. Furthermore, with the consideration of interaction between shale pore walls and gas molecule, mechanical state of gas molecule in various pores of shales is analyzed to determine the critical pore radius for gas occurrence in different types of pores hosted by organic matter and minerals. The control mechanism of micrometer- to nanometer-scale pore structure on shale gas occurrence is elucidated and the total gas capacity of shales is also predicted. It is hoped that the research can perfect theory of shale gas exploration and exploitation, and the findings provide theoretical support and the solving methods for the determination of gas content and reservoir evaluation of shale gas reservoir.

针对当前页岩气藏开发中存在的微-纳米孔隙结构特征认识不足，气体赋存机理不明的问题，项目以四川盆地海相富有机质页岩为研究对象，通过岩石物理实验和地球化学测试，描述页岩储层微观结构特征；采用间接测试和直接观察相结合的方法，定量表征页岩从纳米到微米到宏观的多尺度孔隙结构；开展页岩气高温高压吸附解吸实验，明确页岩吸附甲烷的主控因素，分析页岩储层超临界气体吸附解吸特征；考虑页岩孔隙与气体分子间的相互作用力，阐明气体在页岩孔隙中赋存的微观力学机制，确定页岩有机质和无机矿物中不同类型孔隙赋存吸附气和游离气的临界孔径，揭示页岩微-纳米孔隙结构对页岩气赋存状态的控制机理，并预测页岩储层总含气量。通过上述研究，完善页岩储集层表征和页岩气体赋存机理研究，为页岩储层含气性能确定、储量评价提供理论支撑和解决方法。

页岩复杂的物质组成和多尺度孔隙结构使得页岩储层气体赋存状态复杂化。针对当前页岩气藏开发中存在的微-纳米孔隙结构特征认识不足，气体赋存机理不明的问题，项目以四川盆地龙马溪页岩为研究对象，开展页岩微-纳米孔隙结构表征及其对页岩气赋存状态的控制机理研究，取得了以下研究成果：(1)形成了页岩多尺度孔隙结构定量表征方法，刻画不同岩相页岩从纳米到微米到宏观的孔隙结构及物性特征，明确了富有机质硅质页岩、贫有机质黏土质页岩及混合质页岩的孔隙发育控制因素；(2)通过大量页岩储层高温高压甲烷吸附测试，分析了不同类型富有机质页岩的吸附能力及其控制因素，揭示了水分对页岩气体吸附的影响和机理；(3)阐明了甲烷在页岩孔隙中赋存的微观力学机制，揭示页岩微-纳米孔隙结构对页岩气赋存状态的控制机理；(4)考虑页岩孔隙与气体分子间的相互作用力，建立了适合大温度、压力范围的页岩储层甲烷气体吸附预测模型，预测的页岩储层总含气量与现场实测含气量较为吻合。研究成果为页岩储层特征表征和含气性评价提供理论指导和科学依据，对页岩气藏有效开发具有重要意义。