Directional separation of hydrogen-containing gas mixture by hydrate-membrane coupling method

Recovery of hydrogen (H₂) from H₂-containing gas mixtures has great significance for energy conservation, cost reduction and benefit increase. However, the common separation methods have the ubiquitous problem due to phase equilibrium principle and results in the conflict between H₂ concentration and H₂ recovery rate in the product gas. Consequently, an innovative conception of hydrate-membrane coupling approach is proposed in this work. In the separation process, hydration and membrane permeation two separation driving forces coexist to achieve the aim of strengthening mass transfer kinetics. H₂ and non-H₂ components (hydrocarbons) are synchronously and directionally selected by membrane and hydrate to improve different phase compositions. Therefore, the gas in feed side could keep relatively high two separation driving forces (H₂ fugacity and hydrocarbons fugacity). The results show that the coupling method could synchronously increase both the concentration and the recovery rate of H₂ in the product gas. At the same time, the volume and concentration of the hydrocarbons in hydrate both increases effectively. It indicates that hydrate and membrane separation methods support each other in the separation process. The hydrate-membrane coupling method fundamentally solves the issue of the decreasing driving force resulting from single separation method and phase equilibrium relationship.     

Hydrogen wettability in carbonate reservoirs: Implication for underground hydrogen storage from geochemical perspective

Hydrogen has been considered as a promising renewable source to replace fossil fuels to meet energy demand and achieve net-zero carbon emission target. Underground hydrogen storage attracts more interest as it shows potential to store hydrogen at large-scale safely and economically. Meanwhile, wettability is one of the most important formation parameters which can affect hydrogen injection rate, reproduction efficiency and storage capacity. However, current knowledge is still very limited on how fluid-rock interactions affect formation wettability at in-situ conditions. In this study, we thus performed geochemical modelling to interpret our previous brine contact angle measurements of H₂-brine-calcite system. The calcite surface potential at various temperatures, pressures and salinities was calculated to predict disjoining pressure. Moreover, the surface species concentrations of calcite and organic stearic acid were estimated to characterize calcite-organic acid electrostatic attractions and thus hydrogen wettability. The results of the study showed that increasing temperature increases the disjoining pressure on calcite surface, which intensifies the repulsion force of H₂ against calcite and increases the hydrophilicity. Increasing salinity decreases the disjoining pressure, leading to more H₂-wet and contact angle increment. Besides, increasing stearic acid concentration remarkably strengthens the adhesion force between calcite and organic acid, which leads to more hydrophobic and H₂-wet. In general, the results from geochemical modelling are consistent with experimental observations that decreasing temperature and increasing salinity and organic acid concentration increase water contact angle. This work also demonstrates the importance of involving geochemical modelling on H₂ wettability assessment during underground hydrogen storage.     

自交联型油基钻井液降滤失剂的研制与评价北大核心

针对传统油基钻井液降滤失剂耐温性能不足、影响体系流变等问题,基于自交联改性思路,以N-羟甲基丙烯酰胺为功能单体,与丙烯酸丁酯和苯乙烯进行乳液聚合,研制了一种自交联型油基钻井液降滤失剂(BSN)。通过红外光谱仪、激光粒度仪和透射电镜表征了BSN的主要官能团、微观形貌和自交联特征。实验结果表明,BSN含有自交联功能基团羟甲基,平均粒径为247 nm,颗粒间具有明显的交联结构。热重测试结果显示,BSN热稳定性良好,初始分解温度高达355℃,显著高于非自交联型的降滤失剂BS(278℃)。在油基钻井液体系中添加1%的BSN,不仅不影响体系流变参数而且能够提高破乳电压,180℃下的高温高压滤失量仅为4 mL,滤失控制能力明显优于非交联型的降滤失剂BS以及3%的传统油基钻井液降滤失剂有机褐煤和氧化沥青。     

提升管内颗粒浓度梯度力的特性

由于Kutta-Joukowski横向力与浓度梯度力的共同作用，提升管内颗粒沿径向在边壁大量聚集并形成稳定的环?核结构。根据实验数据，分析了颗粒浓度梯度的径向分布特征，考察了不同操作条件下浓度梯度力系数K的分布特性。由Kutta-Joukowski横向力与浓度梯度的关系，提出了浓度梯度力的表达式Fρ=K(dρ/dr)A及浓度梯度力系数K的表达式K=[?ρg(νg?νp)(?v/?r)r]/?dρ/dr+(d2ρ/dr2)r?。提升管内颗粒群受到的浓度梯度力与浓度梯度力系数K有关。浓度梯度力系数K在提升管中心处为0，沿提升管径向呈“N”型分布，随表观气速增加而增加；提升管内充分发展段K的数值明显大于提升管加速区和出口约束区，总结了浓度梯度力系数K的经验关联式。     

表面润湿性对梯形除雾器分离性能的影响

为解决实际工业中除雾器在高气速时分离效率明显降低的问题，利用除雾器分离实验装置，以水为实验介质，采用电火花线切割技术在叶片表面构建仿生微结构实现表面疏水化，考察了表面润湿性对除雾器分离效率和压降的影响。结果表明，仿生微结构的疏水功能和减阻效应良好，表面液膜的排液速率明显加快。当气速超过5 m/s时，其液膜厚度相对较薄，可有效抑制液滴的二次夹带，提升分离效率。同时，疏水型梯形除雾器内的流场分布较平缓，流动阻力小，总压降约为带钩型梯形除雾器的一半。因此，疏水型梯形除雾器兼具高效率和低阻力特性，综合分离性能最佳。     

气藏采收率影响因素研究与启示——以靖边气田A井区为例

以鄂尔多斯盆地靖边气田A井区为例，采用单因素相关分析和数值模拟方法，对比研究了井网控制程度、储层物性及地层废弃压力对气藏采收率影响及其主次关系。结果表明，井网控制程度是影响采收率的首要因素，井网控制程度每增加10%，采收率提高8.5%；渗透率是影响采收率的重要因素，渗透率每增加10%，采收率平均增加6%；废弃压力对采收率亦有较大影响，废弃压力每降低10%，采收率可提高1.6%。三者对采收率影响综合排序为：井网控制程度>储层物性>废弃压力。分析认为，渗透率是储层固有属性，很难从根本改变；而废弃压力受井口外输压力和增压开采成本制约，降低幅度有限。因此，优化井网及增加井网控制程度是提高气藏采收率的有效途径。研究成果具有实践意义，可为改进气田开发方式和提高气藏采收率提供参考。     

A compositional model for CO2 flooding including CO2 equilibria between water and oil using the Peng–Robinson equation of state with the Wong–Sandler mixing rule

This paper presents a three-dimensional, three-phase compositional model considering CO₂ phase equilibrium between water and oil. In this model, CO₂ is mutually soluble in aqueous and hydrocarbon phases, while other components, except water, exist in hydrocarbon phase. The Peng–Robinson (PR) equation of state and the Wong–Sandler mixing rule with non-random two-liquid parameters are used to calculate CO₂ fugacity in the aqueous phase. One-dimensional and three-dimensional CO₂ flooding examples show that a significant amount of injected CO₂ is dissolved in water. Our simulation shows 7% of injected CO₂ can be dissolved in the aqueous phase, which delays oil recovery by 4%. The gas rate predicted by the model is smaller than the conventional model as long as water is undersaturated by CO₂, which can be considered as “lost” in the aqueous phase. The model also predicts that the delayed oil can be recovered after the gas breakthrough, indicating that delayed oil is hard to recover in field applications. A three-dimensional example reveals that a highly stratified reservoir causes uneven displacement and serious CO₂ breakthrough. If mobility control measures like water alternating gas are undertaken, the solubility effects will be more pronounced than this example.