Abstract
Alkaline-Surfactant-Polymer (ASP) flooding is an efficient chemical enhanced oil recovery (EOR) method gaining popularity in the industry. In this paper, the characteristics of three flooding systems with alkyl aryl sulfonate surfactants and a weak alkali concentration, strong alkali concentration and no alkali concentration were investigated. The emulsification, interfacial tension, viscosity, stability, adsorption resistance as well as the oil displacement effect for the flooding systems and simulated oil of the fourth plant of the Daqing Oilfield were measured. The results show that the three alkyl aryl sulphonates surfactants have different emulsification indexes with the weak and strong alkali concentrations possessing the best and worst indexes at 67.00% and 55.17% respectively, and the combination of surfactant and no alkali concentration with an emulsification index of 63.03%. The interfacial tension between the three flooding systems and the simulated oil of the fourth plant of Daqing Oilfield gets as low as 10−3 mN/m, and reduces as far as 10-4mN/m in certain points detected, all with good anti-dilution performance. In terms of interfacial tension stability, the three flooding systems are seen to reach ultra-low interfacial tension within 90 days. For viscosity stability, the addition of a strong alkali and a weak alkali further hydrolyzes the polymer, leading to an initial rise in viscosity and viscosity retention rates above 80%. In terms of adsorption resistance, ultra-low interfacial tension occurs adsorption is reduced by five times for the strong and weak alkali systems, and reduced by four times for the alkali-free system. These results show that all three combination flooding systems have good adsorption resistance. In the evaluation of oil displacement effect, the average chemical flooding recovery rate (33.83%) of the weak alkali-surfactant-polymer (ASP) system is nearly three percent higher (31.34%) than that of the surfactant-polymer (SP) system, and over seven percent higher (26.71%) than that of the strong ASP system.
Highlights
Alkali-Surfactant-Polymer (ASP) flooding is a new high-efficiency oil recovery technology, which was introduced in the 1980s
The enhanced oil recovery (EOR) of ASP flooding mainly depends on two aspects: one is to improve the viscosity of the system and increase the swept volume; the other is to reduce the interfacial tension of oil and water and produce emulsification to improve oil displacement efficiency[4,5]
The capillary number theory predicts that the oil recovery can be significantly enhanced only when the oil-water interfacial tension reaches ultra-low levels of 10−3 mN/m
Summary
Alkali-Surfactant-Polymer (ASP) flooding is a new high-efficiency oil recovery technology, which was introduced in the 1980s. Performance evaluation of ASP flooding systems consists of alkali, surfactant, and polymer, and fully exerts the synergistic effect of the three components[2]. ASP flooding can increase the swept volume of the displacement phase but can change the wettability of the rock through the adsorption of alkali and surfactant on the rock surface while forming an ultra-low interfacial tension of the oil-water twophase flow to wash out the oil. The EOR of ASP flooding mainly depends on two aspects: one is to improve the viscosity of the system and increase the swept volume; the other is to reduce the interfacial tension of oil and water and produce emulsification to improve oil displacement efficiency[4,5]. The decisive standard for screening surfactants for oil displacement is dependent on whether surfactants can reduce the interfacial tension between oil and water to below 10−2 mN/m under a certain amount of use[8,9,10]
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