Analysis Of Surfactants For EOR

With the developments of enhance oil recovery (EOR) by surfactant flooding, new problems in anaylsis of surfactants especially their mixtures are proposed to the researches. For example in typical alkali-surfactant-polymer flooding the surfactants used are mostly anionics which are easy to analyze, whereas in the surfactant-polymer flooding recently developed anionic surfactants are less or not effective and zwitterionic and nonionic surfactants have to be used which are relatively difficult to analyze quantitatively. Moreover the quantitative analysis of surfactant mixtures is also a problem need to be solved as soon as possible.For this purpose this study focuses on the quatitative analysis of alkylbetaines, fatty amide ethyoxylates and some surfactant mixtures. The results show that alkylbetainescan be transformed to"cationic surfactants"in acid medium which can then be quantitatively determined using two phase-titration method. However, using the two-phase titration method for ordinary ionic surfactants will give underestimated results due to incomplete transformation of the zwitterionic to cationic surfactants. By means of modified method, or adding 3ml 0.1M sulfilic acid into the titration system accurate results can be obtained. Similarly by transforming to cationc surfactants via acidification alkylbetaines can be quantitatively determined by means of automatic potentialmetric titration. Complete acidification can be realized in an acetic acid-asodium-acetate buffer solution with pH=3 by reaction for 2-3hr at 70-80°C, or in a sulfulic acid medium with pH=2 by reaction for 1 h at room temperature. Using a T70 automatic potentialmetric titration instrument, accurate results were obtained for both single long alkylbetaines (C₁₂-C18) and double longalkylbetaine (diC₁₂), with a recovery between 97.00-102.00% and a minimum measurable limit of 3.20×10-5mol/L.The presencof nonionic surfactant does not influence the measurement.It is found that the nonionic surfactants and surfactant mixtures can be quantitatively determined by reverse-colunmn HPLC accompanied with an evaporation-light scattering detector which is in general sensitive to all surfactants and. 8 surfactans, SDS, C₁₂B, C14B, C16B, C18B, diC₁₂B, C₁₂MEAEO1, as well as C₁₂E5 can thus be well separated and determined from their mixture using gradient elution procedure with water/acetonitrile or water/methanol mixture as flowing liquid. As flowing liquid the water/acetonitrile is better than water/methanol for the surfactant mixture by giving a more even-distributeed retension time for each component. Unfornunately the inorganic salts have retention time similar to that of anionic surfactants and thus disturb the analysis of the later. For 8 individual surfactants linear calibration curves were obtained with R2>0.996 and measurable minimum limits being as low as 0.50-6.50μgmL?1, linear concentration range between1.50-5000.00μgmL?1, and recoveries between 96.00-103.00% . The ELST-HPLC method have been successfully applied to the study of surfactant adsorption retention at Daqing sandstone/water ionterface at 45°C, where the adsorption isotherm of C₁₂B based on ELST-HPLC analysis is in good aggremant with that based on chemical analysis, and the adsorption amounts of each component in surfactant mixtures, including binary homologue mixture, binary non-homologue mixture as well multicomponent mixtures, can be determined accurately.