Chemical flooding is a promising technique for enhanced heavy-oil recovery, especially for reservoirs where thermal methods are not feasible. This paper discusses results of a laboratory investigation, including sandpack flooding experiments and micromodel flooding studies, for assessing the suitability and effectiveness of alkaline flooding and alkaline−surfactant (AS) flooding for heavy-oil recovery. The sandpack flood results show that the tertiary oil recovery of AS flooding is lower than those of alkaline-only flooding, although the interfacial tension between the heavy oil and AS system can be reduced to be ultralow. The micromodel tests indicate that the mechanisms for enhanced oil recovery by alkaline flooding are the penetration of the alkaline solution into the crude oil and the subsequent formation of water-in-oil (W/O) droplet flow that tend to reduce the mobility of the water phase and damp viscous fingering, leading to the improvement of sweep efficiency. However, the formation of W/O droplet flow is inhibited with the addition of surfactant, and the viscous oil is easily emulsified into the water phase to form oil-in-water emulsions and then entrains along with the flowing aqueous phase. As a result, viscous fingering phenomena occur during the AS flooding, resulting in a relatively lower sweep efficiency.
The betaine-type amphoteric surfactant exhibits excellent ability in reducing oilÀwater interfacial tension for many kinds of crude oil, but less attention is paid to its adsorption behavior on oil reservoir rock. In this paper, a high-performance liquid chromatography (HPLC) method is established to measure the adsorption of betaine on quartz sand. The mobile phase consists of methanol and water (methanol/water = 90:10 or 85:15 by volume). The column temperature is 40 °C; the flow rate is 1 mL/min; and the sample volume is 20 mL. On the basis of this method, the adsorption of the betaine-type surfactant and sodium dodecyl benzene sulfonate (SDBS) in different conditions was measured and compared. The results indicate that the adsorption of the carboxybetaine-type surfactant and sulfobetaine-type surfactant decreases first and then increases with the increase of the NaCl concentration and reaches relatively low points when the concentration of NaCl is 5 and 10À20 wt %, respectively. The adsorption of SDBS increases with the NaCl concentration monotonically, which is at least 50% higher than that of the betaine surfactant when the concentration of NaCl is over 5 wt %. After Ca 2+ was added to the solution, the adsorption of the betaine-type surfactant on the quartz sand surface, as the opposite case of SDBS, decreases. Moreover, it is found that the adsorption of betaine on the surface of quartz correspondingly decreases with the increase of pH. These behaviors can be explained by the charges of the betaine-type surfactant molecule and the quartz surface. The investigation is instructive for surfactant selection for enhanced oil recovery (EOR).
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