采空区碳封存条件下CO_(2)-水界面特性及溶解传质规律

Research on the characteristics of CO_(2)-water interface and the law of dissolution and mass transfer under the condition of carbon sequestration in goaf

采空区CO_(2)封存作为解决煤炭行业碳排放难题的重要负碳技术储备,在采空区废弃资源二次利用、CO_(2)封存等方面具有广泛的应用前景。利用原位界面张力测定仪开展了不同温压、地层水矿化度及阳离子溶液类型对CO_(2)地层水系统的界面张力(IFT)影响规律实验,明晰了CO_(2)注入含水碎胀煤岩体中的气液界面扩散效应,并将基于统计缔合理论结合兰纳−琼斯势能模型的状态方程(SAFT-LJ状态方程)与密度梯度理论(DGT)结合预测了IFT理论值;利用自主研发的地质封存地化反应模拟实验平台对相同条件下的CO_(2)溶解性进行了探究实验,得到了采空区储层环境下CO_(2)溶解度变化特征,采用D-S模型计算了对应CO_(2)溶解度理论值。实验结果表明:环境温度一定时,采空区储层压力与IFT呈线性负相关关系,储层温度升高,IFT相应增加,但变化幅度较小;温压条件一定时,矿化度与IFT存在正相关性,且在本实验范围内,低压、高温、高矿化度会促使IFT升高;CO_(2)−盐溶液之间的IFT呈现出随着阳离子价态升高而增大的现象(K^(+)<Na^(+)<Ca^(2+)<Mg^(2+));采空区储层压力与CO_(2)溶解度呈正相关关系,当温度为25℃、纯水条件下,压力由0.5 MPa增至2.5 MPa,对应CO_(2)溶解度由0.1627 mol/kg升至0.7141 mol/kg;CO_(2)溶解度随着温度与矿化度的升高而降低;相同质量分数下,一价阳离子溶液(NaCl、KCl)比二价阳离子溶液(CaCl_(2)、MgCl_(2))可溶解更多的CO_(2)。注入采空区中的游离相CO_(2)克服界面张力通过扩散溶解传质作用打破了采空区地层的地球化学平衡,通过明确环境温压条件、采空区水环境对IFT及CO_(2)溶解度的影响规律,阐明CO_(2)地层水气液界面效应及溶解传质机理,以期为采空区CO_(2)封存安全性及封存量评估提供理论基础。

As an important negative carbon technology to solve the carbon emission problem in the coal industry,the CO_(2)sequestration in the mine goaf has a wide application prospect in the secondary utilization of waste resources in the goaf and the capture and storage of CO_(2).In this study,the influence of different temperatures and pressures,formation water salinity and cationic solution type on the interfacial tension(IFT)of CO_(2)-formation water system was investigated by using insitu interfacial tension meter.The gas-liquid interface diffusion effect of CO_(2)injection into water-bearing coal rock mass was clarified.The equation of state(SAFT-LJ equation of state)based on statistical association theory combined with the Lanner-Jones potential energy model and density gradient theory(DGT)were combined to predict the theoretical value of IFT.Using a self-developed geological sequestration and geochemical reaction simulation experimental platform,various exploratory experiments were conducted to investigate the solubility of CO_(2)under the same conditions.The characteristics of CO_(2)solubility variation in the reservoir environment of the goaf were obtained,and the corresponding theoretical values of CO_(2)solubility were calculated using the D-S model.The experimental results show that when the ambient temperature is constant,the reservoir pressure in the goaf is linearly negatively correlated with the IFT value.As the reservoir temperature increases,the IFT value increases correspondingly,but the change range is small.Under constant temperature and pressure conditions,there is a positive correlation between salinity and IFT value.Within the scope of this experiment,low pressure,high temperature,and high salinity promote an increase in the IFT value.The IFT values between CO_(2)-salt solutions show an increasing trend with the increasing valence of cations(K^(+)<Na^(+)<Ca^(2+)<Mg^(2+)).The pressure of the depleted reservoir is positively correlated with the CO_(2)solubility.When the temperature is 25℃ and under conditions of pure water,as the pressure increases from 0.5 MPa to 2.5 MPa,the corresponding CO_(2)solubility increases from 0.1627 mol/kg to 0.7141 mol/kg.The CO_(2)solubility decreases with the increases of temperature and salinity.Under the same concentration,monovalent cation solutions(NaCl,KCl)can dissolve more CO_(2)than divalent cation solutions(CaCl_(2),MgCl_(2)).The free phase CO_(2)injected into the goaf overcomes the interfacial tension and breaks the geochemical balance of the goaf strata through diffusion and dissolution mass transfer.By clarifying the influence of reservoir temperature and pressure conditions and goaf water environment on IFT value and CO_(2)solubility,the gas-liquid interface effect and dissolution mass transfer mechanism of CO_(2)-formation water are clarified,so as to provide a theoretical basis for the safety and evaluation of CO_(2)sequestration in the closed mine goaf.