油藏条件对超临界CO2扩散行为及浓度场分布的影响*

Influence of Reservoir Conditions on the Diffusive Behavior and Concentration Field Distribution of Supercritical CO2

魏 兵 尚 静 相 华 张 翔 刘 江 蒲万芬

WEI Bing SHANG Jing XIANG Hua ZHANG Xiang LIU Jiang PU Wanfen

超临界CO2（ scCO2）在原油中的扩散行为直接决定了其吞吐提高采收率的效果，尤其对于致密页岩等非常 规油藏。本文根据压降法搭建了测定scCO2在原油体相中扩散系数的实验装置，系统研究了压力、温度、原油黏 度等油藏条件对scCO2扩散系数及浓度分布的影响规律，并建立了scCO2浓度场及扩散前缘的预测方法。研究 结果表明，scCO2在原油体相中的扩散系数为10-8 m2 /s数量级，扩散系数随着初始注气压力的升高而增大，最终 趋于平缓；升高温度促进了CO2分子的扩散，但在临界温度点附近出现最大扩散系数；扩散系数随原油黏度增加 快速递减。经过0.4 h扩散，扩散前缘可以完全抵达高度为2.8 cm的油相底部，10 h后scCO2能够完全充满整个油 相空间，在扩散后期，CO2浓度梯度越来越小，扩散速度逐渐降低。图16表1参17

Diffusion of supercritical CO2（scCO2）in crude oil determines the enhanced oil recovery efficiency of huff-puff method， especially in tight and shale unconventional oil reservoirs. In this work，an experimental device was setup to determine the diffusion coefficient of scCO2 in crude oil based on pressure drop method. The influences of initial gas injection pressure，temperature and crude oil viscosity on the diffusion coefficient of scCO2 were investigated. Furthermore，a method of predicting the concentration field and diffusion front of scCO2 in crude oil was established. The results showed that the diffusion coefficient of scCO2 in crude oil was in the order of 10-8 m2 /s and increased with increasing initial pressure and finally reached a plateaued value. The increase of temperature accelerated the molecular diffusion and the greatest diffusion coefficient occurred near the critical temperature of CO2. The diffusion coefficient was found to rapidly decline with the increase of the oil viscosity. After 0.4 h，the diffusion front of scCO2 reached the bottom of bulk crude oil phase，and completely filled the bulk phase after 10 h. In the later stage of diffusion，the concentration gradient of CO2 became low leading to gradual decrease in diffusion.

10.19346/j.cnki.1000-4092.2020.03.013