N_2对CO_2最小混相压力的影响

Effect of N_2 on minimum miscible pressure of CO_2 flooding

向复杂断块油藏注入CO2,既可通过混相驱提高原油采收率,又可节约成本,封存大量温室气体,减缓温室效应。由于断层封闭性及CO2混相均受压力影响,又因注入CO2中常混有N2,因此,文中深入研究N2对CO2-原油最小混相压力的影响。通过Win Prop模块模拟计算了原油分子摩尔质量为170~360 g/mol,油藏温度为310~360 K,N2摩尔分数至10%,约2 000种情况下的混相压力,得到N2影响的CO2混相压力与纯CO2混相压力比值（Fimp）表达式。结果显示,Fimp与注入气体中N2的摩尔分数成正比,不同组成的原油对Fimp没有影响,得到了N2存在情况下CO2-原油最小混相压力的表达式。与CO2混相实验结果及已发表公式计算结果对比发现,该表达式能准确计算N2存在情况下CO2-原油混相压力,为CO2混相驱提高原油采收率及筛选断块油气藏实施混相驱提供理论依据。

Injection of CO2 into complex fault block reservoirs can improve oil recovery, offset the cost, store greenhouse gas and mitigate the greenhouse effect. Since the sealing properties of fault block and CO2 miscible properties are sensitive to pressure, so the selection of the potential reservoir is very critical. Normally CO2 is contaminated by N2, this paper studies the effect of N2 on the CO2-oil minimum miscible pressure. Through Win Prop simulation, about 2 000 sets of the ratio of N2-affected CO2 minimum miscible pressure to pure CO2 minimum miscible pressure（Fimp） were obtained, which have considered the oil molecular weight range in 170-360 g/mol, reservoir temperature in 310-360 K, and the concentration of N2 up to 10%. The results show that the Fimpincreases with the mole fraction of N2. The oil composition has no influence on Fimp. This paper creates a correlation for predicting Fimpwhen N2 exists. Compared with published experimental data and CO2-oil MMP correlations in literature, this new correlation can calculate the N2 contaminated CO2-oil MMP more accurately, which provides theoretical basis for improving oil recovery and screening suitable fault reservoirs for miscible flooding.