Study On Salt Tolerant Heavy Alkylbezene Sulfonate For Enhanced Oil Recovery

Heavy alkyl benzene sulfonate (HABS) is a good surfactant for enhanced oil recovery, but it suffers from a problem of poor salt tolerance. This paper tries to study the possibility of improving the salt tolerance of HABS by mixing with alkylpolyoxy-ethylene ether sulfate (AES), a surfactant with high salt tolerance.The thermal stability of AES was first examined. The results show that the thermal stability of AES in solution is both temperature and pH dependent. In the case of temperature≤80°C and alkaline pH, AES has a thermal stability enough to be mixed with HABS and used in alkali-surfactant-polymer (ASP) flooding.The effects of adding AES on improving the salt tolerance of HABS was studied by means of"tolerant salinity"of surfactant solutions and the optimum salinity, s*, of microemulsions. The tolerant salinity is defined as the maximum salt concentration at which no phase separation appears for a surfactant in aqueous solution at certain concentration and can be determined using spectrophotometry. The results indicated that the tolerant salinity is positively related to s*, and both are good parameters for characterizing the salt tolerance of a surfactant in aqueous solutions.At 45°C the tolerant salinity of HABS in solution at a concentration of 7 mM to three typical electrolytes NaCl, CaCl2 and MgSO4 is only 25, 1 and 1.5 g·L^-1, respectively. With the addition of AES (the total concentration is kept at 7 mM) the tolerant salinity of the mixed solutions to the three salts increases with increasing the mole fraction of the AES. At a AES mole fraction of 0.5, the corresponding tolerant salinity increases to 210, 320 and 340 g·L^-1 respectively. With n-nonane as oil phase, n-butanol as co-surfactant and HABS as surfacatnt, middle phase microemulsion can be obtained by adding NaCl and the optimal salinity s* is found to be 9.5 gNaCl·L^-1. With AES and HABS mixtures as surfactant, s* increases to 16, 28 and 38.5 g NaCl·L^-1 at an AES mole fraction of 0.1, 0.3 and 0.5, respectively. Replacing NaCl by CaCl₂ or MgSO₄, middle microemulsions can only be obtained for mixed surfactant systems where AES mole fraction is higher than 0.3, while no middle microemulsion can be obtained for system containing only HABS as surfactant. On the other hand the solubilization power of the AES/HABS mixture shows a maximum with increasing mole fraction of AES, which means that too much AES will result in a decrease of the solubilization power, or loss of ultralow interfacial tension. The optimum mole fraction of AES in the surfacatnt mixture is between 0.3 to 0.5.