降混剂对二氧化碳在稠油中的溶解度和最小混相压力的影响

Effect of Demixing Agent on Solubility and Minimum Miscible Pressure of Carbon Dioxide in Heavy Oil

于田田 刘廷峰 冯海顺 廖 毅 盖平原 林吉生 高海杰 杨子浩

YU Tiantian LIU Tingfeng FENG Haishun LIAO Yi GAI Pingyuan LIN Jisheng GAO Haijie YANG Zihao

针对CO2 驱油过程中，稠油体系与CO2 难混相，最小混相压力高于地层破裂压力的问题，对CO2 与原油的混合体系进行了分子模拟，考察了降混剂种类和加量、温度、压力的影响。由径向分布函数得到混相过程中CO2 分 子及沥青质分子的聚集程度，进而明确各类分子的分散状态，分析其作用机理。在此基础上，开展高温高压PVT 相态实验，测定CO2 与原油混合体系中添加不同降混剂后的体积膨胀系数和CO2 溶解度，对分子模拟结果进行验证。最后，对柠檬酸三甲酯、苯甲醇、苯甲酸乙酯3种降混剂进行优选，得到最优复配配方，并通过细管实验评价其降混性能。分子模拟结果表明，柠檬酸三甲酯的降混效果最为显著，可有效增大CO2 分子间的聚集程度，降低 沥青质分子间的聚集程度；在高压（6.90MPa）低温（308.15K）的条件下，降混剂更能发挥其作用。PVT相态实验 结果表明，0.23%柠檬酸三甲酯的增溶与增膨作用最佳，与分子模拟结果一致。降混剂最优复配配方为80%柠檬 酸三甲酯+20%苯甲酸乙酯。在原油-CO2 体系中加入0.23%复配降混剂，最小混相压力降幅为21.47%，CO2 溶解 度和原油采收率提高。降混剂含有亲油的烃类基团和亲CO2 的酯基，不仅能与原油体系中的极性分子结合，拆散各沥青分子的聚集体，同时在双亲性能作用下，能吸附在原油与CO2 的界面上，降低原油与CO2 的界面张力，进而降低最小混相压力。

In the process of CO2 flooding，the mixing system of CO2 and heavy oil is immiscible. The minimum miscible pressure is higher than formation fracture pressure. The molecular simulation of the mixing system of CO2 and crude oil was carried out. The effects of the type of downmixing agent，addition amount，temperature and pressure were investigated. The aggregation degree of system of CO2 molecules and asphaltene molecules in the miscible process was obtained by the radial distribution function，the dispersion state of various molecules was defined，and then the mechanism of action was analyzed. On this basis，PVT phase experiments at high temperature and high pressure were carried out to determine the volume expansion coefficient and CO2 solubility of the mixed and crude oil after adding different downmixing agent，which verified the molecular simulation results. Finally， trimethyl citrate，benzyl alcohol and ethyl benzoate were optimized to obtain the optimum mixture formula，and then the performance of reducing miscible pressure was evaluated by the fine tube experiment. The results of molecular simulation showed that trimethyl citrate had the most significant reducing miscible pressure effect，which could effectively increase the aggregation degree of CO2 molecules and reduce the aggregation degree of asphaltene molecules. Under the condition of high pressure（6.90 MPa）and low temperature（308.15 K），the downmixing agent could play its role more effectively. The results of PVT phase experiment showed that 0.23% trimethyl citrate had the best solubilization and swelling effect，which was consistent with the molecular simulation results. The optimum formula of compound downmixing agent was obtained as follows：80% trimethyl citrate，20% ethyl benzoate. The minimum miscible pressure was decreased by 21.47%，meanwhile the CO2 solubility and oil recovery efficiency were improved by adding 0.23% compound downmixing agent to the crude oil-CO2 system. Containing oleophilic hydrocarbon groups and CO2 -philic ester groups，the downmixing agent could not only bind with polar molecules in crude oil system，break up the aggregates of each asphalt molecule，but also adsorb on the interface of crude oil and CO2 under the action of both parent properties，reduce the interfacial tension between crude oil and CO2 ，and then reduce the minimum miscible pressure.

10.19346/j.cnki.1000-4092.2024.01.013