Study On Ultra-low IFT System For Heavy Oil Chemical Flooding

Three kinds of betaine surfactants (carboxybetaine (CBET), sulphobetaine (SBET) and cocamidopropyl betaine (NBET)) were synthesized and the dynamic interfacial tension (DIFT) between the solutions of these surfactants and three kinds of crude oil from Shengli Oilfield were measured. The results indicated that, for Gudao and Gudong heavy oil, CBET-17, SBET-17 and NBET-18 were all efficient in lowering the IFT in the case of no alkalis, while for Shengtuo heavy oil, CBET-17 (0.005%-0.03%) was the best one. These results showed that for different oils, an oil displacement agent with high capacity to lower the oil/water interfacial tension may be obtained only by changing the molecular structure of betaine surfactant, which was a kind of potential surfactant for alkaline-free combination flooding. To investigate the mechanism of lowing IFT for betaine, the DIFT between SBET-17 and the distillate oils of three Shengli crude oil was measured. The results showed that, the interfacial properties between betaine and vacuum residue of these three crude oil were not well, but for other distillate oil, the IFT values decreased correspondingly with the increase of the acid number of distillate oil. Meanwhile, the gas chromatographic (GS) analysis of these three crude oil also showed that, interfacial properties between SBET-17 and the crude oil containing more isoalkanes were much better than those containing more n-alkanes. These study can be used to guide the design of surfactants for alkaline-free combination flooding.A RP HLPC-RID method used to measure the adsorption of betaine is established and optimized. The mobile phase consists of methanol and water (methanol / water = 90:10 or 85:15 by volume), the column temperature is set at 40℃, the flow rate is 1ml/min and the sample size is 20 ml. This method is simple, general, and of high accuracy. Based on this method, the adsorption quantities of betaine and sodium dodecyl benzene sulfonate (SDBS) on quartz sands under different conditions were measured and compared. The results indicate that the adsorptions quantities of CBET and SBET decrease first and then increase with the increase of the concentration of NaCl, and they reach relatively low points when the concentration of NaCl is 5wt% and 10wt% - 20wt%, respectively. While the adsorption quantity of SDBS increases with the increase of the concentration of NaCl monotonically, which is at least 50% higher than that of betaine surfactant when the concentration of NaCl is above 5 wt %. After adding Ca2+ into the solution, the adsorption quantity of betaine on the quartz sands is decreased, which is opposite to the case of SDBS. Moreover, the experiments found that the adsorption quantity of betaine on the surface of quartz correspondingly decreased with the increase of the pH value of the solution.