将CO₂注入不可采煤层地质封存既是降低温室气体效应最理想选择之一，也是煤炭工业降低CO₂排放、实现低碳化可持续发展的必由之路，然而，煤层CO₂地质封存悬而未决的关键问题是：“注入煤层中的CO₂到底能否长期停留而安全封存?”。鉴于此，在弄清煤体CO₂解吸滞后规律的基础上，揭示超临界CO₂解吸滞后机理，建立煤层CO₂地质封存量化模型，探讨利用解吸滞后实现煤层CO₂长期安全封存。研究表明：煤中超临界态CO₂解吸滞后程度大于亚临界态CO₂，在超临界阶段，吸附与解吸等温线形成近似“平行线”的稳定滞后特征；解吸滞后的本质原因是煤中微纳米级亲水性孔隙形成弯液面、产生强大毛细压力、渗吸液态水、截断并固定超临界CO₂流体、最终形成了CO₂残余封存，例如，煤中直径40～10 nm圆柱形无机孔隙可产生7.30～29.12 MPa毛细压力，足以封堵超临界态CO₂；以九里山煤样解吸等温线数据为例，采用基于煤层CO₂解吸滞后的地质封存量化模型，评估出900～1 500 m深部二₁煤层封存总量稳定在35～37 m³/t，其中，吸附封存约占80%，残余封存约占15%，而结构封存仅占5%；解吸滞后启示应尽可能采取措施提高煤层残余封存CO₂比例，原因是毛细堵塞的残余封存CO₂较围岩密封的游离和吸附CO₂更安全且没有泄露风险，煤层灰分、水分、孔隙尺寸和形貌等物性参数是影响残余封存效率的主要因素。

Sequestration of CO₂ in the unmineable coal seams is not only one of the most ideal options for reducing greenhouse gas effects, but also the only way for the coal industry to reduce CO₂ emissions and achieve low carbonization sustainable development. However, the key unresolved issues regarding the CO₂ geo-sequestration in coal seams is: “how long does CO₂ injected into a coal seam remain in the seam?”. In this regard, on the basis of clarifying the hysteresis law of CO₂ desorption in coals, this paper reveals the mechanism of supercritical CO₂ desorption hysteresis, establishes a quantitative model for the geological storage of CO₂, and explores the use of desorption hysteresis to achieve a long-term safe storage of CO₂ in coal seams. The study results shows that the degree of desorption hysteresis of supercritical CO₂ in coal is greater than that of subcritical CO₂, and a stable hysteresis characteristic similar to a “parallel line” in the supercritical phase is formed between the adsorption and desorption isotherm. The fundamental reason for the desorption hysteresis is that the micro and nano sized pores in coal form curved surfaces due to their hydrophilicity, which generate strong capillary pressure following the Laplace’s equation, absorb liquid water, truncate and fix the supercritical CO₂ fluid, and ultimately form CO₂ residual trapping. For example, the cylindrical inorganic pores with a diameter of 40–10 nm in coal can generate a capillary pressure of 7.30–29.12 MPa, which is sufficient to block supercritical CO₂. Taking the desorption isotherm of Jiulishan coal as an example, using the quantitative model for the geological storage of CO₂ established in this study, it has been estimated that the total trapping capacity of the No.21 coal seam at depths of 900–1 500 m is stable at 35–37 m³/t. Among them, the adsorption trapping capacity accounts for about 80%, residual trapping capacity accounts for about 15%, and structural trapping capacity only accounts for 5%. Desorption hysteresis suggests that some measures should be taken to increase the proportion of CO₂ residual trapping in coal seams as much as possible, the reason is that the residual CO₂ sealed by capillary blockage is safer and has no risk of leakage compared to the free and adsorbed CO₂ sealed by surrounding rock. The physical parameters such as ash content, moisture content, pore size, and morphology of coal seams are the main factors affecting the residual trapping efficiency.