Article pubs.acs.org/EF
Experimental Study on Ethanolamine/Surfactant Flooding for Enhanced Oil Recovery Yingrui Bai,*,† Chunming Xiong,† Xiaosen Shang,† and Yanyong Xin‡ †
Research Institute of Petroleum Exploration & Development, PetroChina, Beijing, 100083, China International Exploration and Development Corporation, SINOPEC, Beijng, 100083, China
‡
ABSTRACT: Ethanolamine (ETA) was used together with surfactant to form the ETA/surfactant flooding system. The interfacial tension (IFT) and emulsification of Gudong oil and chemical aqueous solutions were studied. The results indicate that the oil/water IFT can be reduced by 2 orders of magnitude, the oil can be emulsified and dispersed more easily, and the emulsion stability is strengthened due to the synergistic effect of ETA, surfactant, and the in situ soap at the oil/water contact. Seventeen sandpack flooding tests were conducted to investigate the effects of ETA concentration, chemical slug size, chemical slug type, and experimental temperature on the incremental oil recovery. The results show that the highest incremental oil recovery is obtained when 0.065 wt % surfactant and 0.300 wt % ETA are simultaneously injected. In addition, the increase of oil recovery is always accompanied by a sudden pressure drop in the injection process of the ETA/surfactant slug. Larger ETA/surfactant slug size contributes to a higher incremental oil recovery, but there is an optimal slug size (0.8−1.0 PV in the test) when the economic factor is taken into consideration. Moreover, a high experimental temperature has an adverse effect on the synergistic effect of ETA and surfactant because of the volatility of ETA molecules.
1. INTRODUCTION
previous scholars indicate that different kinds of alkaline agents have different adaptabilities to oils. Johnson7 and James8 have summarized four proposed mechanisms of alkaline flooding for enhanced oil recovery: emulsification−entrainment, emulsification−entrapment, wettability reversal, and emulsification−coalescence. James also thought that emulsification may be the most important mechanism in the alkaline flooding. When residual oil contacts the alkaline flooding fluid, different types of emulsions are formed under different kinds of conditions. The viscosity of the emulsion is low when the oil-in-water emulsion is formed. It can be easily flooded out through pore throats, and the displacement efficiency is enhanced consequently.9 When the water-in-oil emulsion is formed, because of the high viscosity, the water channels and pore throats can be blocked by the formed emulsion in the process of its migration. Therefore, more flooding fluid can be diverted to the unswept zone and the sweep efficiency increases correspondingly.10 That is to say, the formation of emulsion contributes to the increase of residual oil recovery. Pei et al.11 and Dong et al.12 also investigated the flooding mechanisms of alkaline agents by using the micromodel and considered that the penetration of alkaline solution into the oil phase and the subsequent formation of emulsion played a crucial role for enhanced oil recovery. Castor et al.13 and Ashrafizadeh et al.14 studied the emulsification and IFT behaviors in alkaline flooding; the result showed that emulsification might be the main mechanism in alkaline flooding and the low IFT effect had a favorable effect on the occurrence of emulsification.
With the deepening of the water flooding development in China, many oilfields have stepped into the development stage of the high or even ultrahigh water cut. With the depletion of the conventional oil reservoirs, a large quantity of residual oil, which cannot be produced via the water flooding, is retained in the pores of the oil reservoirs.1 Tertiary recovery technologies, such as chemical flooding, gas flooding, and thermal recovery, were adopted to extract the residual oil. Among these technologies, chemical flooding, which includes polymer flooding, surfactant flooding, alkaline flooding, and etc., is an effective technology that is applicable to many reservoirs and has been widely used in the oilfields of China.2 Alkaline/surfactant (AS) flooding was once thought to be one of the most promising flooding methods for enhanced oil recovery. The low-cost alkaline agents, such as sodium hydroxide and sodium carbonate, were used together with many kinds of surfactants to enhance the oil recovery efficiency.3 In the AS flooding process, the alkaline agent can react with the organic acids (saponifiable components), which are contained in oil, to generate a surface-active agent (so-called in situ soap) that can lower the oil/water interfacial tension (IFT) and emulsify the oil. Sun et al.4 performed the performance comparison of NaOH and Na2CO3. They found that, although the reaction rate of Na2CO3 and oil was slower than that of NaOH/oil, the ability of Na2CO3 to reduce the oil/ water IFT and emulsify the oil was better due to the buffer effect, and a higher oil recovery was obtained by using the Na2CO3 flooding under the same conditions. Conversely, Ge et al.5 reported that, compared with Na2CO3, NaOH performed better in alkaline flooding for Zhuangxi heavy oils. In addition, Thibodeau6 reported that NaOH and Na2CO3 played the similar role in the flooding of heavy paraffin oil. The studies of © 2014 American Chemical Society
Received: November 25, 2013 Revised: March 4, 2014 Published: March 4, 2014 1829
dx.doi.org/10.1021/ef402313n | Energy Fuels 2014, 28, 1829−1837
Energy & Fuels
Article
Table 1. Compositional Analysis of the Formation Brine Sample ions concentration (mg/L) total salinity (mg/L)
K+ + Na+
Ca2+
Mg2+
CO32−
HCO3−
SO42−
Cl−
3023.5
131.3
21.5
39.8 7508.8
379.6
34.1
3879.0
to evaluate the performance of the ethanolamine/surfactant flooding system for enhanced oil recovery by investigating the IFT and emulsification behaviors and conducting the sandpack flooding tests.
However, the low or even ultralow IFT cannot be obtained easily with the individual application of alkaline agents. To reduce the oil/water IFT significantly, surfactant is added and the surfactant-enhanced-alkaline (AS) flooding technology appears subsequently. The functions of the alkaline agent in the AS flooding have been summarized as follows:8,15 (a) reduce the adsorption of surfactant because of the high pH; (b) form the in situ soap and play the synergetic effect together with the added surfactant; and (c) work as a sacrificial agent to protect the added surfactant by reacting with the divalent and trivalent metal ions. Li et al.16 reported that the residual oil recovery was improved obviously by using the surfactantenhanced-alkaline flooding. Touhami et al.17 also found that the combination of alkaline and surfactant could reduce the IFT more rapidly than alkaline alone. Although the effectiveness of AS flooding is obvious, some shortcomings, such as scale buildup, clay swelling, etc., come out in the flooding process because of the application of inorganic alkaline agents (NaOH, Na2CO3, etc.).18 In Shengli oilfield of China, the alkaline-based flooding is rarely used nowadays due to the serious scale buildup.19 ASP flooding has been widely implemented in Daqing oilfield of China in the 1990s; however, alkali-free SP flooding has been developed in recent years owing to the same reason.20,21 In addition, the alkaline-based flooding cannot be used in many reservoirs of Zhongyuan oilfield because of the high concentration of Ca2+ (>3000 ppm) in formation brine.22 That is to say, the AS flooding technology was applied cautiously and even restrictedly in recent years in China. To minimize the disadvantages caused by inorganic alkaline agents, Berger et al.23 proposed an organic alkali to displace the conventional alkaline agents. He found the following two benefits by using the organic alkali in the laboratory: (a) organic alkali performed equally well in softened and hard brines, and it did not form precipitates with divalent and trivalent metal ions; and (b) organic alkali was as effective as inorganic alkali for reducing the oil/water IFT. Li et al.24 measured the oil/water IFT of triethylamine/sulfonate surfactant solution and Zhuangxi oil. The result showed that the IFT could be reduced to the ultralow magnitude (
