酯类化合物降低原油与二氧化碳体系最小混相压力实验

The experiment for reducing the minimum miscible pressure of crude oil and carbon dioxide system with ester compounds

针对试验区近井地带达到混相驱、远井地带尚未达到混相驱的问题,通过注入油溶性表面活性剂(柠檬酸异丁酯或柠檬酸异戊酯)来降低原油与二氧化碳体系的最小混相压力,该表面活性剂既能够溶于原油中降低原油黏度,又能够溶解在超临界二氧化碳中降低原油与二氧化碳之间的界面张力,从而降低原油与二氧化碳之间的最小混相压力。采用长细管驱替实验的方法,测定了2种油溶性表面活性剂对试验区原油与二氧化碳体系的最小混相压力的影响。实验表明,注入的油溶性表面活性剂能够明显降低试验区原油与二氧化碳体系的最小混相压力,2种表面活性剂降低的最小混相压力值分别为7.2 MPa和6.6 MPa,并且随着表面活性剂注入段塞的增大,测得的原油与二氧化碳体系的最小混相压力逐渐降低,但是降低幅度越来越小,结合表面活性剂制备价格,得到最经济的表面活性剂注入段塞量为0.003 PV,并建议选择柠檬酸异丁酯作为试验区降低最小混相压力的化学试剂。

In the test area,miscible flooding was achieved in the near-wellbore area rather than the far-wellbore area.Aiming at this problem,the oil soluble surfactant（citric acid isobutyl ester or citric acid isopentyl ester）was injected to reduce the minimum miscible pressure of crude oil and carbon dioxide system.This surfactant can not only dissolve in crude oil to reduce the viscosity of crude oil,but also dissolve in supercritical carbon dioxide to reduce the interfacial tension between crude oil and carbon dioxide,thereby reducing the minimum miscible pressure between crude oil and carbon dioxide.The long-slim-tube displacement experiment method was used to measure the influence of two different oil soluble surfactants on the minimum miscible pressure（MMP）of crude oil and carbon dioxide system in the test area.The results showed that the injected oil soluble surfactant was able to obviously reduce the minimum miscible pressure of crude oil and carbon dioxide system,and the MMP reduced by two oil soluble surfactants were 7.2 MPa and6.6 MPa respectively.Moreover,the measured MMP was reduced gradually with constantly increasing the injected slug of surfactant,but the reduction range became smaller and smaller.The most economical injected slug of surfactant was 0.003 PV by evaluating the cost for surfactant preparation.It was suggested that the citric acid isobutyl ester should be chosen as the chemical reagent to reduce the MMP in the test area.