| The alkaline-surfactant-polymer (ASP) technology was initialed in 80s in 20thcentury. Actually, alkalinities are used to replace surfactant activity partly orcompletely for this technology so that the activity is usually lowered in the range of0.03% to 0.3% (active). Usually, both retention and adsorption on reservoir sandstonefor chemicals of surfactant and polymer used are obviously decreased. The percentageof chemical loss, especially for expensive surfactant, is higher than that of 50%. Thesynergy between an alkaline and the petroleum soap, which is resulted from theinteraction between organic acid alkaline, is favoured in oil recovery. Obviously, notonly the sweep efficiency, but also the displacement oil efficiency for ASP is improvedcompared to polymer technology. So the ASP will probably be an important method inEOR in the future.At the state of art, the ASP technology is still investigated in laboratory orpilot.Through a lot of laboratory investigation and the field test results showed thatthe Oil-water equilibrium interfacial tension geting to10-3mN/m orders of magnitude,can make oil recovery increased by over 20% OOIP than water flooding.Therefore,ASP water-oil interfacial tension must achieve 10-3mN/m orders of magnitude, hasbecome the key technology limits of Asp flooding formula screening and theimportant technical "hard" index of the system selection and evaluation of thesurfactant of ASP .Meanwhile this technology boundaries brought the following two questions:First, technology boundaries increased screening difficulty of Surfactantsystem,Also limited the type and source of surfactants;Second, only high concentrations of alkali to meet 10-3mN/m orders ofmagnitude of ultra-low balance interfacial tension,this would greatly improve thecost of chemical agent of ASP flooding, hamper the popularization and application ofASP technology . But, with the following two interfacial tension characteristicsof surfactants were more easily producted and gain:1.Water-oil interfacial tension can long-term stable balance of 10- 2mN/m ordersof magnitude .2.Oil-water balance interfacial tension fell short of 10-3mN orders of magnitudeof ultra-low value, but minimum dynamic interfacial tension value can achieve 10 -3 /m orders of magnitude .If the theoretical and experimental can prove that the Oil DisplacementEfficiency of these two kinds of surfactant systems and the Oil DisplacementEfficiency of balance interfacial tension reaching 10-3mN/m orders of magnitudewere quite,so the most domestic industrial surfactant products can be used in ASPflooding, thus greatly reduced strict requirements and restrictions of ASP flooding ,greatly widened the sources and selectivity of surfactant .On the basis of researching achievements at home and abroad, this paperanalyzed and studied origin theory of the required minimum interfacial tension ofresidual oil,the mechanism of Water-oil interfacial tension on trecovery influenceand effective analysis of the interfacial tension.The results of the study showed thatWater-oil interfacial tension reaching 10-2mN/m orders of magnitude still caneffectively enhance the recovery, in the meantime provided the reasonable choice ofsurfactant and combination, a new concept and lberated the harsh condition thatwater-oil interfacial tension must achieve 10-3mN/m orders of magnitude .The results in this paper imply that the oil recovery increases with the decrease ofinstantaneous(or dynamic) or equilibrium IFT between crude oil and surfactant brineon strongly oil wet rock (θO=10°～45°).The curve represents"S". The oil recoveryover waterflood increases slowly with the decrease of IFT if IFT≥4.5×10-1mNm orIFT≤4.5×10-2mNm,and the oil recovery over waterflood is almost reached a maximumor a constant as IFT≤4.5×10-2mNm while the oil recovery over waterflood increasessharply with the decrease of IFT if IFT arrange from 4.5×10-1mNm to 4.5×10-2mNm.Oil displacement test results on cores display that 20%OOIP of oil recovery overwaterflood as instantaneous(or dynamic) minimum IFT being 4.5×10-2mNm is almostequal to that as equilibrium IFT being lowered to the ultralow magnitude of 10-3mN/m.This implies most commercial surfactants could be used in ASP because theinstantaneous (or dynamic) minimum IFTs between their alkali solution and crude oilare easily lowered to 4.5×10-2mN/m even if alkalinity decreases deeply or withoutalkaline.Conclusions based on core flooding tests give obviously that the instantaneous(ordynamic) minimum IFT effect strongly on oil displacement efficiency, or the mainfactor which effects oil recovery is the instantaneous(or dynamic) minimum IFT, but equilibrium IFT.According to this paper core displacement experiment result, choose the lowestorders of magnitude reaching 10-2mN/m of the compound system,including: ASPsystem of daqing oilfield formula , as well as under the condition of lower alkaliagent, and even without alkali,using surfactant/polymer dual compound system toimplement core displacement experiment, to the correctness of the above conclusion .Test results showed that whether reducing alkali agent by 25% 45% or Nonalkaliconditions, effect of commercial surfactants composite system for coredisplacement experiment were very ideal, improving oil recovery about 20% OOIPthan wter flooding . |
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