离子对CO2-盐水系统界面特性的影响

应用分子动力学模拟的方法对不同浓度及组分比例的CO₂-NaCl、CO₂-CaCl₂和CO₂-（NaCl+CaCl₂）等CO₂-盐水系统的界面张力进行了研究,从分子层面上分析了不同种类的盐离子对界面张力的影响。结果表明,盐离子的存在会增加CO₂-纯水的界面张力,界面张力增量主要由阳离子电荷数导致,其余则由阳离子兰纳-琼斯势参数、原子质量等原子特性参数引起;3种系统的界面张力增量均与离子强度呈线性关系,且其曲线的斜率和盐溶液种类无关,为IFT预测提供理论指导。     

CO2-烃类液相混合物比定容热容的实验与模型研究

近年来,二氧化碳(CO₂)提高原油采收率(CO₂-EOR)技术得到了广泛的研究。充分了解CO₂-烃类混合物的热容性质是该项目能够成功实施的基础,但是目前对此性质的研究非常有限。基于绝热量热法,搭建了一个绝热量热计,测量了温度为317.15~353.15 K,压力高达29.49 MPa时,CO₂-碳氢化合物(正己烷、正辛烷、十一烷、环己烷、乙苯)二元液相混合物的比定容热容(C_v )数据,共获得335个数据点。此外,采用预测模型(结合热力学关系的PR状态方程)和经验模型计算C_v,计算平均绝对相对偏差(AARD)分别为0.81%~3.66%和小于2.56%。经验模型的形式简单,但PR模型有较强的预测能力。实验测得的C_v 数据以及建立的两种计算模型对CO₂-EOR项目的实施至关重要。     

二氧化碳在稠油中溶解度的测定与模型预测

选取华东地区某油田的稠油作为研究对象,采用静态高压相平衡装置,在温度363.15、368.15、373.15 K下,测定了压力2~22 MPa 范围内CO₂-稠油体系的气液两相的平衡组成。将稠油看作假一元组分,通过基团贡献法估算了稠油的临界参数,分别采用P-R 方程和改进的P-T 方程拟合关联所测得的实验数据,得到了CO₂-稠油体系的二元作用参数,最后计算了CO₂-稠油体系的相平衡数据,结果表明改进的P-T 方程的拟合结果要明显优于P-R 方程,更适用于高温高压下CO₂-稠油体系溶解度的数据预测。     

温度及压强对CO2-盐水系统界面张力的影响

在超临界态CO₂封存于深部盐水层过程中,温度、压强等控制条件是影响封存效率和封存量的重要因素。应用分子动力学模拟的方法对343～373 K和6～35 MPa范围内的CO₂-NaCl盐水系统进行了界面张力（IFT）及界面特性的研究,分析了IFT随温度及压强的变化关系,并观测到了压力平衡点p_plateau;从分子尺度（物质密度、界面过余量、界面水合物密度）分析了IFT随压强、温度的变化,以及p_plateau产生的原因。结果表明,p_plateau前压强升高或温度降低将导致CO₂密度升高,IFT下降,而p_plateau后IFT趋于稳定且受温度影响较小;CO₂的界面过余量及界面处水合物数量随压强及温度变化,与IFT的变化相反;高压下界面水合物密度的饱和现象可能是p_plateau产生的重要原因。     

CO2浓度对混溶态(CO2+正己烷)/盐水界面微观特性的影响

在CO₂以超临界状态封存于油气藏时,储层中流体间的界面性质是影响封存效率和封存量的重要因素。利用分子动力学模拟的方法,对330 K、20 MPa混溶条件下(CO₂+正己烷)/NaCl溶液系统的界面微观性质进行了研究,分析了混溶相中CO₂摩尔分数变化时,界面处CO₂和正己烷的亲水、疏水特性及其影响,为CO₂地质封存提供理论依据。研究发现,随着混溶相中CO₂摩尔分数的增加,界面厚度及粗糙度增大,分子渗透加深,热波动加剧。界面上CO₂与水之间更强的相互作用造成了CO₂注入过程中界面张力的降低。CO₂表现出类似于表面活性剂的性质,并在CO₂摩尔分数为65%(质量分数为50%)时,其界面累积量以及正己烷的驱离量最大。界面处存在特殊的分子微观结构,CO₂、水及正己烷分子呈现特殊的排布方式。     

CO2对长庆采出油水物性影响及乳状液稳定机理

二氧化碳(CO₂)驱作为一项日益完善的采油技术，已经成为提高低渗油田采收率的重要手段，具有适用范围广、开采成本低和洗油效率高等优点。然而，由于CO₂特殊的物理和化学性质，其采出液稳定性较常规水驱明显增强，为采出液处理带来了困难。通过光学显微镜、动态光散射、流变学等方法，研究了在不同压力下CO₂处理对长庆原油和采出水的物性以及所形成的油包水(W/O)型乳状液稳定性的影响，探究了CO₂驱采出液乳化和稳定的影响因素。结果表明，随着CO₂压力的增大，CO₂驱采出水中Ca²⁺和Mg²⁺质量浓度均有所下降，而CO₃^2-与HCO₃^-总体含量有所增加，水相pH值略下降，从弱碱性转变为弱酸性。CO₂处理导致原油中轻质组分减少，胶质沥青质等重质组分的含量升高，原油极性增强。CO₂处理后油的反常温度和析蜡...     

低质量流速下超临界CO2在管内冷却换热特性

开展了低质量流速下超临界CO₂在水平直管内冷却过程的换热特性的实验研究。实验压力为p=7.5~9.0 MPa,质量流速为G=79.6~358.1 kg·m^-2·s^-1,流体温度为25.0~50.0℃。分析了质量流速、压力、流体温度对换热的影响,并引入Richardson数阐述浮升力对超临界CO₂在水平直管内冷却换热影响。实验结果表明: 传热系数随着质量流速的增加而增大。传热系数峰值点随压力的升高向高温区偏移。当质量流速较小时,传热系数峰值点出现在准临界温度之前,且浮升力作用加大,流体处于混合对流状态。将传热系数的实验值和已有的换热关联式计算值作对比后发现在低质量流速下误差较大,拟合了低质量流速工况的超临界CO₂在水平直管内冷却换热的关联式,94%的实验值和拟合关联式误差在±20%范围内。     

镁掺杂四氧化三钴催化环己烷氧化初步研究

以金属有机骨架材料(ZIF-67)为前驱体负载氧化镁(MgO)，制备氧化镁/四氧化三钴(MgO/Co₃O₄)并用于环己烷催化氧化。采用X射线衍射(XRD)、红外光谱(FT-IR)、CO₂程序升温脱附(CO₂-TPD)、透射电镜(TEM)等表征技术对MgO/Co₃O₄催化剂进行系统研究。结果表明：低MgO负载量时，MgO与Co₃O₄颗粒均匀分布，两相之间的作用导致部分Mg离子掺杂进Co₃O₄骨架中；在高MgO负载量时，MgO发生严重的团聚，致使其与Co₃O₄的作用减弱。MgO/Co₃O₄-x的催化活性随MgO负载量的增加呈现先增强后减弱的趋势，MgO/Co₃O₄-0.6显示出最佳催化性能，环己烷转化率达到16.5%时，环己醇和环己酮选择性之和...     

313.15 K下三元体系KH2PO4-(NH2)2CO-H2O相平衡研究

采用等温溶解平衡法研究了三元体系KH₂PO₄-(NH₂)₂CO-H₂O在313.15 K下的溶解度数据,根据溶解度数据绘制了等温相图,采用湿渣法和X射线衍射法对平衡固相的组成进行了分析。结果表明三元体系KH₂PO₄-(NH₂)₂CO-H₂O为简单共饱和型体系,相图中有1个共饱和点、2条单变量曲线、3个结晶区;采用Wilson和NRTL模型关联该体系的溶解度数据,关联计算值与实验值基本吻合。其中Wilson模型的相对平均偏差(RAD)和均方根差(RMSD)分别为3.34%、0.17%;NRTL模型的RAD和RMSD分别为10.53%、0.38%。对比三元体系KH₂PO₄-(NH₂)₂CO-H₂O在多个温度下相平衡的结晶区域,发现在中、低温阶段降低温度有利于尿素[(...     

CO2管道输送技术研究

在油田三次开采和碳捕集、利用与封存(CCUS)技术发展的背景下，将CO₂注入地层可以有效提高原油采收率，同时减少碳排放，缓解温室效应。CO₂输送是CCUS工程建设的重要环节之一，其中管道输送以输送量大、距离远、经济性好等优点一直备受关注。根据纯CO₂相态图，阐明了不同相态下CO₂温度压力范围，对4种相态下管道输送工艺流程进行分析，得出对于短距离CO₂管道，选择气相和液相输送较为合理；对于长距离CO₂管道，选择密相和超临界相输送较为合理。从管道输送工艺和经济性评价2个方面，探讨了国内外CO₂管道输送技术研究进展，并结合国内外已建CO₂管道案例，对国内CO₂管道输送技术研究提出建议。     

CO2-原油体系发泡特性实验研究

为研究CO₂驱油田分离器内泡沫层产生及消除机理,设计了一套高压溶气原油泡沫测试系统,采用降压法研究了CO₂-原油体系的发泡特性。利用高速摄像机对泡沫产生至衰变的演变过程进行了记录,总结分析了不同降压阶段的气泡行为,研究了降压速率和搅拌速率对原油发泡特性的影响规律。研究发现,随压力降低,稳定存在气泡的直径增大,气泡位置上移,发泡行为更加剧烈;降压速率增加对降压阶段的发泡行为无明显影响,但会加剧稳定工作压力下的发泡行为;在转速小于等于120 r/min的条件下,搅拌速率增加会加剧降压阶段的发泡行为,但会加速稳定工作压力下的泡沫衰变。     

多孔介质内超临界CO2流体及泡沫驱油特性的比较实验研究

CO₂混相驱替可以提高原油采收率,因此近年来得到研究者们的广泛关注。使用高温高压驱替设备,利用超临界CO₂流体、超临界CO₂泡沫及N₂泡沫作为驱替介质,对油水饱和孔隙介质中的油相驱替特性开展了比较实验研究。通过对驱替过程沿程压力及对驱替增采油量的测量,对不同驱替手段在孔隙介质内的油相增采特性进行深入研究和探讨。研究发现在温度为50℃、压力为13 MPa时,超临界CO₂流体对多孔介质内的油相驱替效果有显著提升,当压力进一步升高到23 MPa时,油相增采效果不明显。说明在本实验条件下超临界CO₂流体与油相在50℃、13 MPa时可达到混相驱替状态;而采用超临界CO₂泡沫及N₂泡沫注入工艺未能进一步提高出油量。沿程压差测量结果则显示,与N₂泡沫相比,超临界CO₂泡沫在多孔介质试样内的驱替压差较小,起泡性能较差。实验结果对于筛选及评价超临界CO₂驱油工艺具有一定的指导意义。     

基于GA-BP神经网络的超临界CO2传热特性预测研究

超临界二氧化碳（S-CO₂）动力循环在能源利用领域中拥有广阔的应用前景,其中超临界CO₂的传热特性对其能量转换效率至关重要。开展了超临界CO₂在水平小圆管内对流传热实验研究,并通过建立遗传算法优化的BP神经网络模型（GA-BP）,对其在不同工况下的传热特性进行预测分析。实验参数范围：系统压力7.5~9.5 MPa,质量流速1100~2100 kg/（m²?s）,热通量120~560 kW/m²。实验结果表明,超临界CO₂传热系数随流体温度的升高先增大后减小,在拟临界温度附近达到最大值。GA-BP神经网络模型能有效地预测超临界CO₂的传热系数,预测数据的决定系数R²为0.99662,超过95%的数据误差位于±10%范围内,平均误差为3.55%,为超临界流体传热预测提供新的思路。     

CO2 SOLUBILITY IN WATER AND BRINE UNDER RESERVOIR CONDITIONS

The reference Henry's constant was determined from 110 solubility data found in the literature for the CO₂/H₂O system over a temperature range of 298 to 523 K and a pressure range of 3.40 to 72.41 MPa. Since the Krichevsfcy-llinskaya equation was used to model the system, a correlation for the A parameter was also developed.

In addition to the Krichevsky-Ilinskaya equation, another two-parameter correlation for the solubility of carbon dioxide in water was obtained by using the Krichevsky-Kasarnovsky equation. The reference Henry's constant and partial molar volume of carbon dioxide at infinite dilution were treated as adjustable parameters. The calculated values of the partial molar volume at infinite dilution did not correspond to experimentally determined values found in the literature. Therefore, a third correlation for the reference Henry's constant was obtained by using the Krichevsky-Kasarnovsky equation in conjunction with the correct values of the partial molar volume. This one parameter (Henry's constant) model did not fit the experimental data as well as the two-parameter models.

The decreased solubility of CO₂ in brine was accounted for empirically by a single factor correlated to the weight percent of dissolved solids. A literature data set of 167 solubilities, with a temperature range of 298 to 523 K and a pressure range of 3.0 to 85.0 MPa, was used to develop this correlation. A wide scatter of data characterizes this correlation, which relates the CO₂ solubility in brine to the CO₂ solubility in water at the same temperature and pressure. The correlation is designed for applications in which the determination of concentrations of individual ions is impractical and the implementation of only one additional parameter is desirable, such as the use of compositional simulators to model miscible displacement in the petroleum industry.

These correlations can be easily implemented into reservoir simulation calculations to account for the effects of CO₂ solubility in brine. These effects are often ignored even though they can have dramatic effects on the performance of the CO₂ enhanced oil recovery process. The correlations presented in this paper for the Henry's constant and the effect of dissolved solids can adequately account for these CO₂ solubility effects.     

Conformance control by a microgel in a multi-layered heterogeneous reservoir during CO2 enhanced oil recovery process

Injecting CO₂ into the underground for oil displacement and shortage is an important technique for carbon capture, utilization and storage (CCUS). One of the main problems during the CO₂ injection is the channeling plugging. Finding an effective method for the gas channeling plugging is a critical issue in the CO₂ EOR process. In this work, an acid-resistance microgel named dispersed particle gel (DPG) was characterized and its stability was tested in the CO₂ environment. The microgel size selection strategies for the homogeneous and heterogeneous reservoirs were respectively investigated using the single core flooding and three parallel core flooding experiments. Moreover, the comparison of microgel alternate CO₂ (MAC) injection and water alternate CO₂ (WAC) injection in the dual core flooding experiments were presented for the investigation of the role of microgel on the conformance control in CO₂ flooding process. The results have shown that the microgel featured with —NH and C—N groups can keep its morphology after aging 7 days in the CO₂ environment. Where, the small microgel with unobstructed migration and large microgel with good plugging efficiency for the high permeability zone were respectively featured with the higher recovery factor in homogeneous and heterogeneous conditions, which indicate they are preferred used for the oil displacement and conformance control. Compared to WAC injection, MAC injection had a higher incremental recovery factor of 12.4%. It suggests the acid-resistance microgel would be a good candidate for the conformance control during CO₂ flooding process.     

水合物法平衡级分离CO2/N2流程模拟分析

化石燃料燃烧排放烟气中CO₂的量占CO₂总排放量的75%,为了缓解CO₂导致的全球温室效应,需将CO₂/N₂中的CO₂分离出来。水合物法分离是一种高效、低能耗的CO₂/N₂分离技术。本文研究了水合物法平衡级分离CO₂/N₂过程中,进料CO₂体积分数、反应条件与反应特性三者间的关系,利用CPA-SRK方程+Chen-Guo模型对其进行平衡级分离流程模拟分析。经计算发现,进料干基CO₂体积分数对水合物法分离CO₂/N₂工艺的反应压力、平衡级级数均有较大影响。随着体积分数的增加,反应压力呈减小趋势,减小幅度随体积分数增加而减小,当进料CO₂体积分数小于20%时,压力下降较快,当体积分数大于50%时,压力降低幅度变小。温度为277K时,CO₂体积分数小于10%时,需四个水合物平衡级分离才能得到满足要求的气样;当体积分数为10%~20%时,需三个水合物平衡级分离;体积分数大于30%时为两个水合物平衡级分离。温度对水合分离的反应压力有较大影响,但对所需平衡级分离级数的影响并不大。随着温度的升高,水合反应压力呈增加趋势,增加幅度随进料干基CO₂体积分数的增加而降低。针对所研究气样,在不同温度下,均需三个水合物平衡级分离才能达到工艺要求。     

Adsorption behavior of carbon dioxide and methane in bituminous coal: A molecular simulation study

The adsorption behavior of CO₂, CH₄ and their mixtures in bituminous coal was investigated in this study. First, a bituminous coal model was built through molecular dynamic (MD) simulations, and it was confirmed to be reasonable by comparing the simulated results with the experimental data. Grand Canonical Monte Carlo (GCMC) simulations were then carried out to investigate the single and binary component adsorption of CO₂ and CH₄ with the built bituminous coal model. For the single component adsorption, the isosteric heat of CO₂ adsorption is greater than that of CH₄ adsorption. CO₂ also exhibits stronger electrostatic interactions with the heteroatom groups in the bituminous coal model compared with CH₄, which can account for the larger adsorption capacity of CO₂ in the bituminous coal model. In the case of binary adsorption of CO₂ and CH₄ mixtures, CO₂ exhibits the preferential adsorption compared with CH₄ under the studied conditions. The adsorption selectivity of CO₂ exhibited obvious change with increasing pressure. At lower pressure, the adsorption selectivity of CO₂ shows a rapid decrease with increasing the temperature, whereas it becomes insensitive to temperature at higher pressure. Additionally, the adsorption selectivity of CO₂ decreases gradually with the increase of the bulk CO₂ mole fraction and the depth of CO₂ injection site.