煤层碳封存背景下CO2-水-煤/岩地球化学作用及其对盖层封闭性的影响

In the process of CO2 sequestration in coal seams with enhanced coal bed methane recovery (CO2-ECBM), the sealing capacity of overlying caprock determines the operation of CO2-ECBM on a large time scale. Based on the site-specific data from the coal seam in Shanxi Formation of CO2-ECBM project, located in the Southeast of Qinshui Basin, China, by the means of field survey, data collection and analyses, laboratory experiments, numerical simulations and natural analogy, this proposal proposes to investigate the geochemical reactions of CO2-water-coal/rock after CO2 injection; analyze the transport mechanism of trace and toxic elements; illuminate the invasion mechanism of CO2 from the coal seam into the caprock; reveal the responses of porosity, permeability and geochemical properties to the presence of CO2; construct a two-phase fluid flow, solution transport and chemical reaction model available for the low porosity and permeability media to quantitatively study the CO2-water-coal/rock interaction and its influence on the evolution of caprock sealing capacity on a geological time scale. By combining with natural analogy method, the simulation results are expected to be validated. The proposed project will provide basic theory and technology for site selection and safety assessment of CO2-ECBM.

强化煤层气（CH4）开采的深部煤层封存CO2（CO2-ECBM）过程中，煤储层上覆盖层的封闭性能决定着整个CO2-ECBM工程能否长期安全稳定运行。以山西沁水盆地东南部CO2-ECBM工程山西组煤层系统为研究对象，采用野外调查、资料搜集分析、室内实验、理论分析、数值模拟和天然比拟手段相结合的技术方法，研究超临界CO2注入煤层后所发生的一系列CO2-水-煤/岩地球化学反应，分析微量、有毒元素迁移转化机制，阐明CO2入侵盖层机理，揭示盖层地球化学特征、孔隙度、渗透率等对CO2入侵的响应规律；构建适于刻画低渗透性盖层中CO2-水两相流体流动、溶质运移、化学反应全过程的耦合模型，定量研究CO2-水-煤/岩地球化学作用及其对盖层封闭性长期演化的影响，并结合天然比拟法对模拟结果的可靠性进行验证。该项目的研究成果可以为今后CO2-ECBM工程选址、深部煤层CO2封存安全性评估提供基础理论依据和技术支持。

强化煤层气（CH4）开采的深部煤层封存CO2（CO2-ECBM）过程中，煤储层上覆盖层的封闭性能决定着整个CO2-ECBM工程能否长期安全稳定运行。本项目以山西沁水盆地东南部CO2驱煤层气工程山西组煤层系统为主要研究目标，针对CO2在煤层封存过程中发生的一系列问题开展了系统研究。通过该项目研究在以下方面得到重要进展：(1)CO2参与情况下煤层矿物发生溶蚀，促进煤层中金属微量元素释放和迁移，温度的升高有助于煤中元素的迁移；(2)煤层上覆盖层的钙质泥岩与CO2、水反应比较强烈，CO2以白云石和菱铁矿等碳酸盐矿物被固定下来，导致盖层渗透性降低，增强了盖层的封闭性；(3)开发了基于有限数据实现地层孔渗与岩石矿物特征空间非均质化软件，能够将产生的孔隙度、渗透率和岩石矿物含量落在观测值范围内的概率控制在99.74%，为开展CO2长期地质封存泄漏风险评价提供模拟工具；(4)提出了基于天然CO2气藏类似物剖析数据开展大时间尺度地球化学数值模拟结果可靠性验证技术，并给出岩石矿物冲刷系数的确定方法，为开展CO2地质封存及资源化利用研究提供基础理论及技术支持。