Note N <sub> 2 </ Sub> Gas To Improve The Experimental Study Of Feasibility Of Low-permeability Reservoir Recovery

The price of N₂ has become cheap with the development of N₂-producing technology since 1980s,moreover, it's wide source, free of erosion and pollution make it the new technology during the process of injecting gas to enhance oil recovery especially for low-permeability reservoir, condensate gas reservoir and steep structural reservoir.To study the feasibility of injecting N₂ in Shengli oil field, we have established the main principle of district selection on the basis of the researches on some related laboratory studies and field applications, screened out Niu-20 fault block as the optimal district to carry out N₂ flood in shengli oilfield according to above principle and choosed the representative oil, gas, water and core samples to carry out systematical laboratory investigation against the geological condition of the selected district。 The research including: the phase behavior study of the N₂ and crude oil, i.e. the experimental research of the expansion and visbreaking N₂ exerting on crude oil, the multiple-contact experimental research of N₂ and crude oil; the interfacial-tension study of N₂ and crude oil; the minimal-mixture-pressure study of N₂ and crude oil. Meanwhile, we use long core physical simulation method to study the effect of injection pattern and injection time on N₂ flooding.The results show that, the mutual solubility and visbreaking capacity of N₂ on crude oil in Niu-20 fault block formation is poor, N₂ is incapable of extracting light hydrocarbon component in quantities and decreasing the interfacial tension between displacing phase and displaced phase, it's hard to carry out the multiple-contact miscible displacement of N₂, but N₂ can reduce both viscosity and density of crude oil to some extent, improve mobility ratio; N₂ is able to expand crude oil and increase movable oil, improve elastic energy of formation effectively, enter the micro-pore which water can't sweep to sweep out more oil. So the non-miscible flooding of N₂ can still enhance the recovery of low-permeability reservoir if choose the better injection pattern. moreover, the optimized way for gas injection resulted from long core physical simulation can enhance oil recovery more than 15%—24%.This result show that (even in non-miscible flood mode) can improve the oil recovery efficiently in low-permeability reservoir, especially for a WAG process with an advanced CO₂...