深部煤层注CO2的矿物地球化学行为及储层物性响应机理

The CO2 geological storage to enhance coalbed methane recovery (CO2-ECBM) is a viable option to reduce the greenhouse gas emission with the benefit of production of coalbed methane, which is regarded as a cleaner energy from coal. Under the dual action of supercritical CO2 fluid and groundwater, the material composition and physical properties of coal reservoir will be changed, affecting the effectiveness of CO2 storage and CH4 displacement. However, further studies regarding the mechanism of geochemical action are needed. Taking the typical medium-high metamorphic coal samples as the main research object and the temperature-pressure conditions of deep coal reservoir as the simulated experimental conditions, a series of experiments will be designed to simulate the mineral geochemical processes with injecting scCO2 into deep coal seams. The core technique is the localization observation and quantitative characterization of the same mineral and pore-fractures (nano-micron scale) before and after the geochemical reaction. Comprehensive analysis of samples before and after the reaction will be conducted by combining the pore-fracture structure analysis, the establishment of three-dimensional pore-fracture network model, the testing of reservoir physical parameters, mineral and element analysis, geochemical reaction simulation analysis and other methods. The geochemical behavior of minerals and elements, and the response mechanism of physical properties of coal reservoirs in the scCO2-H2O-coal system will be revealed. The mechanism of complex geochemical action will be illuminated from the microscopic scale. The influence mechanism of coal metamorphism, temperature-pressure and reaction time on geochemical effects will be clarified.

深部煤层CO2地质存储与CH4强化开采集温室气体减排与新能源开发为一体，极具前景。在超临界CO2流体与地下水的双重作用下，煤储层物质成分与物性特征发生改变，影响了CO2封存与CH4驱替的有效性，其地球化学作用机理有待进一步探讨。本次研究选取沁水盆地中-高变质程度煤为研究对象，以深部煤储层原位温压状态为实验条件，模拟scCO2注入深部煤层的地球化学作用过程。以反应前后同一矿物、孔裂隙（纳米—微米级）的定位观察与定量表征为核心技术手段，结合反应前后样品的孔裂隙结构分析、三维孔裂隙网络模型构建，储层物性参数测试、矿物/元素分析、地球化学反应模拟分析等，查明scCO2-H2O-煤岩体系中矿物及元素地球化学行为、煤储层物性特征。微观尺度阐明scCO2注入煤储层的地球化学作用机理，探讨煤变质程度、温压条件与反应时间对地球化学效应的影响机理。

煤层CO2地质存储与CH4强化开采（CO2-ECBM）是“碳中和”背景下煤地质学研究的重要领域。高压注入深部煤储层的CO2以超临界状态赋存（scCO2）。在scCO2和地层水的双重作用下，煤基质和无机矿物的赋存特征的改变可导致煤物性参数的变化，影响CO2-ECBM的有效性。项目选择不同变质程度的煤作为研究对象，以深部煤储层原位温压状态为实验条件，模拟scCO2注入不同埋深煤层的地球化学作用过程。（1）通过对反应前后同一矿物颗粒的观察结合固体和液体的元素分析证实了scCO2的注入导致主量元素迁移率高，在局部平衡作用下有微量石膏和铝硅酸盐沉淀。随着反应时间的延长，碳酸盐矿物几乎全被溶解，样品表面可见1微米长的碳酸盐结晶。（2）利用微米级背散射图，结合原位孔隙观察、高压压汞、液氮和CO2吸附数据阐明了ScCO2-H2O-煤岩反应增加了煤的脆性、孔隙度、大孔孔容和比表面积，孔隙连通性和孔隙复杂程度。表明了煤阶是控制孔隙结构变化的主因，温压条件与反应时间对大孔影响更为明显。（3）利用NMR渗吸实验、NMR等温吸附实验、覆压孔渗、CT等手段分别揭示了ScCO2-H2O-煤岩作用提高了煤的润湿性、吸附性、及渗透性，并发现了连通孔隙扩展方向，及煤岩物性变化程度受各向异性的影响特征。（4）基于矿物与孔隙的原位观察与定量表征，查明了scCO2-H2O-煤岩反应体系中地球化学作用类型，揭示了其对煤储层孔裂隙演化的作用方式与影响范围，阐释了碳酸盐矿物形貌与含量对储层物性变化的影响机制。揭示了温压条件与反应时间影响了地球化学反应程度，而煤阶则决定了样品固有特征及其可改造程度。本次研究的相关成果可为深部煤层CO2-ECBM、煤矿采空区CO2封存、以及煤系气CO2封存提供重要的理论依据。