| Currently, water injection is used as second development in many oilfields at home and abroad, but the injection isn’t enough for oil recovery, beccuase there is still a certain amount of oil remaining in the formation. As an eco-friendly and efficient production methods, foam flooding plays a good role in enhanced oil recovery (EOR), which has been studied for more than three decades. Foam flooding has been applied in EOR for the oilfields and made very good achievements. With increasing in exploration and demanding for petroleum resources, low-permeability reservoirs have become an important target of exploration and development in the future in China. However the domestic researches and applications about foam flooding systems are rarely reported in high-salinity and low-permeability reservoirs. Therefore, it is of great significance to study a good foam flooding system for the reservoirs.On the basis of reducing the production cost of raw materials, the synthesis route is designed by avoiding the use of expensive propane sultone and sodium hydride. In this paper, a series of sulfonate Gemini surfactants are synthesized by etherification (Connecting hydrophobic group), ring-opening reaction, sulfonation reaction (Connecting hydrophilic group) and etherification (Connecting connection group), with fatty alcohol, epichlorohydrin,1,2-dichloroethane, sodium sulfite, sodium hydrogen sulfite, tetrabutylammonium bromide and so on, their hydrophobic groups containing C8H17, C10H21and C12H25(Ⅲa,Ⅲb and Ⅲc) respectively. The surface tension, critical micelle concentration, melting point and Krafft point of the products are measured. With the increase of the hydrophobic chain, cmc and γcmc are decreased. Compared with conventional surfactants, cmc of the products decline1-3orders of magnitude. Their melting points are above100℃and their krafft points are below zero. The structures of products are characterized by infrared spectroscopy. The results show that the molecular structure of the products is consistent with the product which expected to get. The products have excellent salt resistance, which mainly depends on four ether bonds and the two adjacent sulfonic acid groups.Researches indicated that the product Ⅲc has the highest surface activity and the best salt resistance, which is selected to foaming agent for later and compared with six other kinds of surfactants about the foaming ability. Effect of foaming agent concentration, temperature and salinity on foaming ability of these surfactants are researched. According to Foam Composite Index (FCI), the preferred concentration of foaming agent is0.40wt%at the reservoir temperature and salinity. The three surfactants Ⅲc, AOS and SDS are identified to have good foam properties. Ⅲc/AOS complex system is selected for the high-salinity and low-permeability reservoir such as Yianchang oilfields.The effect of the temperature, salinity, rock wettability and crude oil on the foaming volume and half-life of the complex system are studied. Experimental results show that the complex system has good temperature resistance and salt resistance. Experiments find that the foaming ability of the complex system is enhanced slightly in the presence of salt solution. The foam disappears slowly on water-wet surface, while the foam disappears quickly on oil-wet surface. The micro-morphology of the foam is observed, and it is a regular hexagon. When the amount of crude oil is less than10%, the complex system presents good oil resistance. The core displacement experimentations show that foam flooding can enhance recovery by17.1%and improve water injection profile very good. |
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