Abstract:

Deep saline aquifers, characterized by wide distribution, large storage capacity, and low competition with oil and gas resources, are widely regarded as ideal media for geological CO₂ storage. This study elucidates the dissolution and diffusion behavior of CO₂ in real formation water under complex temperature-pressure conditions is of great significance for improving storage efficiency and ensuring long-term safety. Taking the Jurassic Sangonghe Formation in the Junggar Basin as the research object, a NaHCO₃ - type formation water model containing Na⁺, K⁺, Ca²⁺, Mg²⁺ and ions was constructed based on regional geological and hydrochemical data. Molecular dynamics simulations were then performed to systematically investigate the dissolution behavior, density distribution, intermolecular interactions, and diffusion mechanisms of CO₂ in formation water under varying temperature and pressure conditions. The simulation results indicate that under isothermal conditions, pressure is the dominant factor controlling CO₂ occurrence and dissolution. Low pressure favors rapid dissolution of CO₂, moderate pressure enables efficient utilization of storage capacity, and high pressure helps maintain long-term system stability. Under isobaric conditions, elevated temperature markedly enhances CO₂ solubility by weakening hydrogen bonding and intensifying molecular thermal motion, thereby promoting uniform dispersion of CO₂ molecules and the formation of stable solvation structures. Under coupled temperature-pressure conditions, the CO₂ adsorption amount increases significantly with burial depth in the low-pressure interval (approximately 1000~4000 m), indicating a strong promotion of dissolution by pressure increase; in the high-pressure interval (>4000 m), the adsorption continues to increase but with a decreasing rate, reflecting that temperature-induced desorption gradually offsets the promoting effect of pressure. In addition, the diffusion coefficient shows a stratified trend: elevated temperature in shallow zones promotes CO₂ molecular migration, whereas high pressure in deep zones significantly suppresses diffusion, with a relatively small overall variation. Comprehensive analysis suggests that the depth interval of 1000~4000 m is the most suitable range for CO₂ geological storage, as it ensures both high dissolution efficiency and long-term stability. This study elucidates the microscopic mechanisms of CO₂ dissolution and diffusion in formation water under complex temperature-pressure conditions, deepens the understanding of CO₂ fluid occurrence and migration in deep geological environments, and provides scientific guidance for evaluating storage potential, selecting suitable storage sites, and designing injection strategies, offering valuable references for CCUS engineering practice.

Key words: CO₂ geological storage, formation water, temperature-pressure coupling, dissolution and diffusion mechanism, storage potential evaluation, molecular simulation

摘要：

深部地层水因分布广泛、封存潜力大且与油气资源竞争性低，被普遍认为是CO₂地质封存的理想场所。本研究系统揭示了在复杂温压条件下CO₂于真实地层水中的溶解与扩散规律，对提高封存效率与安全性具有重要意义。本研究以准噶尔盆地侏罗系三工河组为研究对象，结合区域地质与水化学数据，构建含Na⁺、K⁺、Ca²⁺、Mg²⁺以及HCO₃^-离子的NaHCO₃型的地层水模型。随后采用分子动力学方法，系统模拟了不同温压条件下CO₂在地层水中的溶解规律、密度分布、分子间相互作用以及扩散机制。模拟结果表明，在恒温条件下，压力是影响CO₂赋存与溶解的主控因素：低压阶段有利于CO₂在地层水中的快速溶解；中压阶段可实现封存容量的有效利用；高压阶段有助于维持体系的长期稳定。恒压条件下，温度升高显著增强了CO₂的溶解能力，尤其在高温区间，氢键作用被削弱、分子热运动增强，促进了CO₂分子的均匀分布与溶剂化结构的形成。在温压耦合作用下，吸附量在常压段(约1000~4000 m)随埋深增加显著上升，说明压力的升高显著促进了CO₂在地层水中的溶解；在高压段(>4000 m)，吸附量虽继续增加但增幅趋缓，反映出温度升高导致的脱附效应逐渐增强，部分抵消了压力的促进作用。此外，从扩散系数变化趋势来看，浅部温度升高可促进CO₂分子迁移，而深部高压则显著抑制扩散，整体变化幅度较小。综合分析表明，1000~4000 m是CO₂地质封存的最适宜深度区间，该区间兼具较高的溶解效率和长期稳定性。研究揭示了复杂温压条件下CO₂在地层水中的溶解与扩散微观机制，深化了对深部CO₂流体赋存与迁移规律的认识，为深部咸水层封存潜力评价、封存层位优选及注入方案设计提供了科学依据，对CCUS工程实践具有重要指导意义。

关键词: CO₂地质封存, 地层水, 温压耦合作用, 溶解和扩散机制, 封存潜力评价, 分子模拟

CLC Number: 

• P618.13

• TE133