Effects of block and random copolymerization on the properties of fatty alcohol polyoxypropylene-polyoxyethylene ether sulfates for enhanced oil recovery

Enhanced oil recovery (EOR) by surfactant flooding has been attractive. Among the surfactants developed alcohol polyoxypropylene (PO)-polyoxyethylene (EO) ether sulfates (APES), also named extended surfactants, have been proved efficient. However, the arrangement of the PO and EO chains as well as the hydrocarbon structure in the molecules may significantly affect their performances. In this paper three APES, C18-16PO25EO10SO4Na (I), C18-16(PO/EO)25+10SO4Na (II), and C16GA(PO/EO)25+10SO4Na (III) were prepared and investigated, in which APES (I) and APES (II) were designed to have same PO and EO numbers but block and randomly copolymerized respectively with linear C18-16 fatty alcohols as starting agent, whereas the APES (III) was derived from double chain C16 Guerbet alcohol (C16GA) with PO and EO randomly copolymerized. The results show that the block copolymerized APES (I) gives much better brine solubility and counterion tolerance than the randomly copolymerized APES (II) and (III). Although all APES synthesized are highly surface-active and can reduce Daqing crude oil/simulated brine interfacial tension (IFT) to ultralow by mixing with more hydrophobic surfactants in presence or absence of alkali, the APES (III) gives the lowest IFT due to with double hydrocarbon chains. In addition, it is found that for APES (I) gelation occurs in neutralization process and the corresponding nonionic intermediate is highly viscous, whereas the randomly copolymerized two intermediates are liquid-like with low viscosity, which may be feasible to apply SO3/air falling film sulfation. This study provided useful information for arrangement of embedded nonionic moiety and hydrocarbon structure in designing extended surfactants for EOR.