Study On The Displacement Behavior Of Non-alkali Ultra-low Interfacial Tension System

Surfactant/Polymer binary flooding has become a research hotspot both in domestic and overseas recently,it could effectively avoid the adverse effects of alkali on displacement process and ground equipment.Aiming at the problem of low efficiency and unclear evaluation index of SP flooding system design method,the index of improving the recovery rate of the non-alkali ultra-low interfacial tension flooding system was clarified,an optimization method for SP compound system was established,based on the construction of alkali-free ultra-low IFT flooding system and investigation of phase behavior and oil washing rate.Firstly,the acid number?0.622 mg KOH/g?and equivalent alkane carbon number?7?of Zhuangxi 106-15-X18 crude oil were determined.Ultra-low interfacial tension?IFT?surfactant compound system was constructed through a large number of compound systems of anionic and nonionic surfactants firstly.Flooding system formulas are:0.3 wt%6501/SS231?6501accounted for more than 50%??0.3 wt%KPS/SS231?2:1,1:1?.The IFT for Zhuangxi oil can reach 10^-3 mN/m,which could meet the standard of tertiary recovery.Phase behavior experiments showed that for the four flooding systems of 6501/SS231?3:1?,6501/SS231?2:1?,KPS/SS231?2:1?and KPS/SS231?1:1?,the optimum salinity range with simulated oil phase were 2.4-2.8 wt%NaCl,over 4.5 wt%NaCl 1.8-2.1 wt%NaCl and 2.4 wt%NaCl,respectively.The optimum salinity range with crude oil were 3.0-3.6 wt%NaCl,2.7-3.0 wt%NaCl,1.6-2.0wt%NaCl and 3.2-4.0 wt%NaCl,respectively.Finally,washing experiments and physical model experiments were evaluated for the SP flooding system.The oil washing rate of the four flooding systems were 52.01%,47.77%,43.33%and 39.67%respectively.The lower dynamic IFT between the system and crude oil is,the higher the washing rate could get.The physical model experiments showed that with the system of KPS/SS231?2:1?,the oil recovery value could be enhanced by 63.46%,65.18%,61.61%when the salinity were 2.0?2.2?0.5 wt%NaCl respectively.When the salinity of compound system was slightly higher than optimum salinity,the highes ultimate recovery as well as enhanced recovery could be got,and there was still potential when displacement was finished.Therefore,the optimum salinity is considered as the optimal standard for the non-alkli ultra-low interfacial tension flooding system,the optimum salinity could be determined by phase experiments.When the displacement is carried out under the condition of a slightly higher salinity,oil recovery could be maximized.