Study On The Decrease Of Miscibility Pressure On CO₂ Flooding By Fatty Alcohol Polyether Surfactant

How to decrease effectively the minimum miscibility pressure?MMP?of CO₂ and crude oil is one of hot and difficult issues in CO₂ flooding research.However,research on the decrease of MMP is initiated just now.There is no one efficient way to decrease the MMP for CO₂ flooding.In this work,several special nonionic surfactants were adopted to reduce the interfacial tension of CO₂/crude oil,and then reduce the MMP significantly.To find an excellent fatty alcohol polyether surfactant which can reduce MMP of CO₂ and crude oil,the thesis studies on several different surfactants.Also,the change law of MMP with different factors were researched.The mechanism that surfants reduce MMP of CO₂ flooding could be explained on theory.The main conclusions are as follows.The fatty alcohol polyoxypropylene ethers and polyoxyethylene ethers were synthesized and characterized by MS.The result showed that they are all narrow distribution with different polymerization degree.The total content of fatty alcohol polyether with two similar polymerization degree in more than half.There is almost no other carbon chain length of the fatty alcohol or its derivative.The research results of fatty alcohol polyether surfactants and other factors showed that the method that the MMP was calculated using straight-line extrapolation by hanging drop is credible.C₁₂PO₆ is the most efficient surfactant to reduce the MMP of CO₂/crude oil,more efficient than polyoxyethylene ethers-6.The MMP for CO₂ flooding can be further reduced by adding ethanol,and shows variation with different addition amount of surfactant and promoter.The MMP for CO₂ flooding could be reduced from 17.79 MPa to 13.22 MPa,more than 26%,at C₁₂PO₆ dosage of 0.6 wt%?based on the weight of CO₂?,ethanol dosage of 0.7wt%,and the temperature of 333.15 K.Furthermore,C₁₂PO₆ could decrease the MMP efficiently in the temperature range of 323.15 K³53.15 K.With temperature increased,the MMP for CO₂ flooding first decrease and then increase,best at 333.15 K.The results suggested that the effect laws of the CO₂-philic group and oelophilic group on MMP obtained from the DPD simulations are in agreement with those from the experimental data.The MMP of CO₂/alkane system increases with the increase of temperature.And the MMP increases significantly with increasing the carbon chain length of alkane.The surfactant molecules tend to distribute in the interface layer of CO₂ and oil,but the distribution state of surfactant could be affected by the surfactant structure closely.The MMP of CO₂/C16 could be reduced by means of the addition of fatty alcohol polyoxyethylene ether or fatty alcohol polyoxypropylene ether,and the addition of PO_m-C_n is more effective.The MMP decreases with the increasing of polymerization degree of CO₂-philic group?PO?when the polymerization degree is relatively low.However,the MMP begins to increase,reversing previous trends,with continuing increase of polymerization degree after 6.Similarly,the MMP decreases with the increasing of carbon chain length of oelophilic group when the carbon chain length is relatively low,but the MMP begins to increase with continuing increase of carbon chain length after 12.