超临界CO_2-水两相流与CO_2毛细捕获:微观孔隙模型实验与数值模拟研究

CO_2毛细捕获机制是CO_2地质封存中的关键科学问题,然而有关孔隙尺度下(微米极)超临界CO_2毛细捕获的研究较少.采用高压流体-显微镜-微观模型实验装置,开展超临界CO_2条件(8.5 MPa,45?C)下CO_2驱替水(排水)和水驱替CO_2(吸湿)实验,采用高分辨率照相机采集CO_2水两相流运动图像,并借助光学显微镜直接观测孔隙尺度下CO_2毛细捕获特征.同时,采用计算流体动力学方法对实验过程进行三维数值模拟.数值模拟不仅反映了实验过程中两相流驱替锋面的推进过程,还刻画了孔隙尺度下被捕获的CO_2液滴/团簇三维空间形态特征.最后,基于数值模拟给出了CO_2初始饱和度与残余饱和度曲线,即毛细捕获曲线,并对比分析了3种毛细捕获曲线预测模型(即Jurauld模型、Land模型和Spiteri模型)的优劣.分析表明,Jurauld模型的描述能力稍优于Land模型,Spiteri模型的描述能力较弱.由于Land模型只需单个参数,且参数具有明确的物理意义,因此在实际工程中,建议优先采用Land模型.

SUPERCRITICAL CO2 WATER DISPLACEMENTS AND CO2 CAPILLARY TRAPPING:MICROMODEL EXPERIMENT AND NUMERICAL SIMULATION

The CO2 capillary trapping is an important scientific issue in geological carbon sequestration, but few re-searches focus on the trapping mechanism at pore scale under supercritical CO2 condition. In this study, based on the high-pressure fluids-microscopy-micromodel experimental system, we performed drainage experiment, i.e. supercrit-ical CO2 displacing water, and imbibition experiment, i.e. water displacing CO2, under the conditions of 45?C and 8.5 MPa. The DSLR camera was used to capture pictures of CO2-water two-phase immiscible flow and the microscopy was used to capture the capillary trapping behavior for the supercritical CO2 at the pore scale. The computational fluid dynamic method was adopted to simulate the two-phase fluid flow processes. The numerical results are generally in agreement with the experimental observations, and further provide three-dimensional geometries on the interface during the drainage-imbibition processes and the trapped supercritical CO2 droplet/cluster. Finally, the capillary trapping curve, i.e. the relationship between the initial CO2 saturation and the residual saturation, was obtained from the numerical results, and we made an assessment of the three capillary trapping models, i.e. Land's, Jurauld's and Spiteri's trapping models. A comparison of the models performance indicates that Jurauld's model behaves slightly better than Land's model, whereas Spiteri's model behaves poorly. However, given that Land's model only contains one parameter of clear physical meaning, it is recommended for practical use.