煤层—砂岩差异储渗机制下气、水流动行为

Coalbed methane (CBM) and tight sand gas (TG) in coal-bearing strata are important unconventional natural gas resources, with similar gas source and overlapping layers. However, the material composition (organic/ inorganic), gas storage mechanism (adsorption/ desorption), and gas production process (de-pressure or not), are different between coal and sandstone, of which the differences between gas and water storage and their migration mechanism restrict the co-production of CBM and TG. Thus, the middle rank coals in east margin of Ordos basin is chosen as a case study, based on technologies of “Quantitative characterization of gas and water in situ” and “Dynamic simulation experiment of gas and water production” of differentiated gas systems. The project would clarify the differences between coal and sandstone combinations through macro and micro observations; analysis the gas and water in situ accumulation status through experiment of water saturation and relative permeability under various temperature and pressures; simulate the gas and water flow behaviors under different stress conditions, physical parameters, reservoir pressure and drainage methods through designing experiments of parallel connected coal and sandstones. The above research concentrates on “reservoir quality and permeability differentiation of coal and sandstones — gas and water storage and flow mechanism — integrated production of unconventional gases”, and the results would improve the understanding of controlling factors of unconventional reservoirs and promote the comprehensive exploitation of unconventional resources within coal-bearing strata.

煤系煤层气和致密砂岩气是重要的非常规天然气资源，两者气源相近且叠置发育，但煤—砂岩在物质组成（有机/无机）、储气机理（吸附/游离）和排采方式（降压与否）等方面均有不同，其中气、水赋存和流动机制的差异，制约了煤—砂含气系统中气体的协同产出。针对上述问题，拟以鄂尔多斯盆地东缘中煤阶为研究对象，围绕差异含气系统“气、水原位赋存定量表征技术”和“气、水产出动态模拟实验技术”，通过宏观—微观含气系统的刻画，查明煤层和致密砂岩含气组合的差异性；测试不同温度和驱替压差下的含水饱和度和渗透性，分析原位地质条件下气、水赋存机制；设计煤层和砂岩合层排采“并联”实验，模拟不同应力环境、储层物性、气藏压力和排采手段影响下的气、水流动规律。上述研究以“煤层和砂岩的储渗差异发育特征—气水赋存、流动机制—资源综合开发可行性”为主线，对阐明煤系非常规储层可采性控制因素，实现煤系非常规天然气资源的综合开发具有积极意义。

煤系气在近年受到普遍关注，煤层本身及其上覆地层能够形成具有工业开发价值的致密气和页岩气藏，综合勘探这些非常规天然气将有助于提高国家天然气供给。.本项目以鄂尔多斯盆地东缘上古生界等为例，揭示了上古生界叠置含气系统。太原、山西、下石盒子组气藏开发潜力大。太原组受频繁海侵的影响，山西组沉积环境相对稳定，下石盒子组砂岩具有良好的产气潜力。流体包裹体证据表明，白垩纪是主要生烃期。开展了煤层—砂岩合采物理模拟实验研究，砂岩气与煤层气合采贡献率随时间呈交叉的“X”型分布，砂岩层压力越大、煤层压力越小，或砂岩层出口端压力越小、煤层出口端压力越大，煤层气产出量反超砂岩气所需时间越长。研究区页岩总有机碳含量平均1.3 wt%，以Ⅲ型干酪根为主，成熟到高成熟阶段，具有良好的产气潜力，黏土矿物直接影响页岩孔隙结构和孔径非均质性。.本次研究的相关成果有助于阐释煤系多元气藏的物性条件、产出机制和综合开发可行性，对实现煤系非常规天然气资源的综合开发，提高地下天然气资源的产出效率具有重要意义。