N₂对CO₂最小混相压力的影响

Effect of N₂ on minimum miscible pressure of CO₂ flooding

 李康宁¹ 宫厚健¹ 王冲² 李润虎³ 龙菲菲¹ 董明哲¹

中国石油大学（华东）石油工程学院，山东 青岛 266580 中国石油长庆油田公司勘探开发研究院，陕西 西安710018 中国石油长庆油田分公司第一采油厂，陕西 延安 716000）

College of Petroleum Engineering, China University of Petroleum, Qingdao 266580, China Research Institute of Exploration and Development, Changqing Oilfield Company, PetroChina, Xi′an 710018, China No.1 Oil Production Plant, Changqing Oilfield Company, PetroChina, Yan′an 716000, China)

 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WinProp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（F_imp）表达式。结果显示，F_imp与注入气体中N2的摩尔分数成正比，不同组成的原油对F_imp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 WinProp 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 Fimp increases with the mole fraction of N₂. The oil composition has no influence on Fimp. This paper creates a correlation for predicting Fimp when 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.

10.6056/dkyqt201606016