CO2地质封存条件下矿物溶解动力学机制及盖层有机质的萃取效应研究

The greenhouse CO2 geological storage is a hot topic in the world. There are several types of acid high-pressure CO2 fluid underground interacted with water-rock. The theory and experiment study is very crucial for such CO2-water-rock systems. However, it is lack of CO2-water-rock experimental data in the range of pressur and temperature under CO2 geological storage. Transition State Theory (TST) is used to get the relationship between reaction rate and Gibbs free energy for mineral dissolution kinetics, which is not reasonable for near-equilibrium CO2 geological storage systems. There is also lack of study on cap rock sealing performance after supercritical CO2 fluid extraction. Therefore, calcite and shale are selected as typical mineral and cap rock for CO2-water-rock/mineral interaction under 25～80℃ and 5～12MPa using self-made experimental apparatus. Scanning transmission electron microscope, environmental scanning electron microscope, synchronous radiation instrument, etc. are used to characterize rock and mineral particles. We can get the calcite dissolution kinetics from far-from-equilibrium to near-equilibrium and mineral micro-surface changes. For different content and occurrence of organic matter in cap rock shale, the effect of shale sealing ability parameter, such as porosity, permeability and micro-scale appearance, is also discussed before and after supercritical CO2 fluid extraction. This project is useful for well understanding supercritical CO2-water-rock/mineral interaction and CO2 safe storage, which would be of great scientific and practical importance.

温室气体CO2地质封存是国内外关注热点，地下高压酸性CO2流体存在多种形式与水岩作用，相关理论和实验研究具有重要意义。由于(1)地质封存CO2温压范围内实验数据基本空白；(2)以往通过速率与吉布斯自由能的关系，运用过渡态理论研究矿物溶解动力学机制，对长期封存环境下近平衡态体系不能适用；(3)缺乏超临界CO2对盖岩萃取作用影响其封闭性能的对比研究。因此项目选取典型矿物方解石和不同页岩盖层，在25～80℃、5～12MPa，通过自制实验装置进行CO2-水-岩/矿物作用研究，结合透射电镜、环境扫描电镜、同步辐射仪等手段，获取地质封存CO2条件下从远离平衡态至近平衡态方解石溶解动力学机制和矿物表面微区信息，以及超临界CO2萃取不同含量和赋存状态的有机质页岩，对其孔隙度、渗透率及微区形貌的变化影响。项目对深入认识超临界CO2与水-岩(矿物)相互作及安全地质封存CO2，具有重要科学意义和应用价值。

温室气体CO2地质封存是国内外关注热点，地下高压酸性CO2 流体存在多种形式与水岩作用，相关实验研究具有重要理论和实际意义。项目选取典型矿物方解石、长石、橄榄石、黏土等以及页岩、砂岩，在不同温度和压力下，通过自制实验装置进行CO2-水-岩/矿物作用研究，结合透射电镜、扫描电镜、X射线衍射分析等手段，获取地质封存CO2条件下矿物（岩石）溶解动力学机制和矿物岩石表面微区信息。得到如下认识：（1）CO2-水-泥（页）岩作用实验表明不同相态区对反应影响显著，超临界条件下作用最激烈。（2）CO2-水-页岩作用实验证实了有机质的萃取效应，含有少量水的超临界CO2能够明显携带岩石中有机质进入水体造成潜在污染。（3）CO2-压裂液-页岩作用实验表明储层岩石的溶解能产生更多微孔隙存在环境风险。（4）CO2-水-砂岩作用实验表明高温超临界条件导致储层成岩作用与孔隙演化。（5）CO2-地层水-砂岩作用实验表明储层岩石孔隙生成可增大渗透率。（6）CO2 (N2)-橄榄石作用实验证实了矿物表面的活化机制和过渡带形成的作用。（7）CO2-橄榄石作用实验证实了黏土矿物的存在加速溶解反应的作用机制。（8）CO2-地层水-粘土矿物作用实验表明蒙脱石和绿泥石的溶解会导致次生矿物形成并影响岩石矿物稳定性。（9）CO2 (SO2)-咸水-碳酸盐和硅酸盐矿物对比实验，证实了方解石和长石在混合气体中更容易加速溶解并影响CO2地质封存效果。（10）CO2-水泥-咸水作用实验发现硫酸根存在导致石膏而非方解石沉积在水泥表面，有助于保护水泥不会进一步受到CO2侵蚀，减缓碳酸盐化速度。（11）生物炭-水体-土壤相互作用及其环境效应研究表明，生物炭除了地表碳封存作用，还有助于农作物产量的提高，优化实验条件开发的磁性生物炭能用于水中六价铬的去除，土壤中通过添加生物炭能有效抑制重金属和有机污染物的迁移，起到原位锁定的作用。