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Systematic investigation of the effects of zwitterionic surface active ionic liquids on the interfacial tension of a water/crude oil system and their application to enhance crude oil recovery Han Jia, Peng Lian, Yipu Liang, Yanguang Zhu, Pan Huang, Hongyan Wu, Xu Leng, and Hongtao Zhou Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b02746 • Publication Date (Web): 05 Dec 2017 Downloaded from http://pubs.acs.org on December 12, 2017
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Graphical Abstract
Two zwitterionic surface active ionic liquids were evaluated for their higher interfacial activity and exhibited a satisfactory displacement performance in core flooding tests.
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Systematic investigation of the effects of zwitterionic surface active ionic liquids on the interfacial tension of a water/crude oil system and their application to enhance crude oil recovery Han Jia*, Peng Lian, Yipu Liang, Yanguang Zhu, Pan Huang, Hongyan Wu, Xu Leng, Hongtao Zhou*
School of Petroleum Engineering, China University of Petroleum (East China), Qingdao, 266580, China
Abstract Two zwitterionic surface active ionic liquids (SAILs), 3-(1-hexadecyl-3-imidazolio) propanesulfonate
(C16IPS)
and
3-(1-hexadecyl-3-imidazolio)
propanesulfonate
β-naphthalene sulfonate (C16IPS-Nsa), were evaluated for their potential application in chemical enhanced oil recovery. It was found that the zwitterionic SAILs had a higher interfacial activity than the traditional SAILs. Interestingly, the C16IPS-Nsa molecule with the large hydrophobic group β-naphthalene sulfonate had a greater ability for reducing the interfacial tension (IFT) of water/crude oil. Moreover, the systematic investigations of the dynamic IFT and the salt and temperature effects further confirmed the proposed mechanism of two zwitterionic SAIL effects on the IFT. The C16IPS-Nsa system exhibited a satisfactory displacement performance (15.3% of initial oil in place), which may be attributed to the transient minimum value (~10-3 mN/m) in its dynamic IFT curve.
Corresponding author: Han
Jia, Tel.: +86-532-86981663.
E-mail address:
[email protected]; Hongtao Zhou, Tel.: +86-532-86981901. E-mail address:
[email protected]. 1
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1. Introduction Surfactant flooding is a powerful method to improve the recovery of residual oil trapped by capillary force.1 Surfactants can reduce the oil/water interfacial tension (IFT) or modify the formation wettability to effectively increase the microscopic oil displacement efficiency.2-4 During the past three or four decades, many kinds of surfactants have been introduced to various aspects of the petroleum industry, especially for IFT reduction in enhanced oil recovery (EOR).5-10 Due to the wide resource and low cost, anionic surfactants (petroleum sulfonate, petroleum carboxylate, and alkylbenzene sulfonate) have been used extensively in conventional reservoirs.11 However, the poor salt and temperature tolerance may restrict their further application in oil reservoirs. Zwitterionic surfactants contain a cationic hydrophilic group and an anionic hydrophilic group connected by the covalent bond in one molecule. The special molecular structure endows the zwitterionic surfactants with many excellent properties, such as low toxicity, good salt tolerance, good temperature tolerance, and so on.12 These unique advantages make the zwitterionic surfactants ideal candidates for EOR, which has attracted considerable attention.12-19 Zhang et al. systematically investigated the effects of fatty acids, crude oil fractions, and inorganic alkalis on the IFT of zwitterionic surfactant solutions/crude oil.17-19 The authors found that the zwitterionic surfactant decreased the IFT of brine solutions/crude oil to ultra-low values at low concentrations (0.1 wt%). Due to the specific physical and chemical properties, surface active ionic liquids (SAILs) have shown the desired ability to reduce the IFT, thus greatly improving crude oil recovery.20-26 Recently, our group demonstrated the high interfacial activities of the anionic SAIL and mixed SAIL systems.25,26 All of the above-mentioned publications have focused on the use of cationic or anionic ILs. However, there are few reports on zwitterionic ILs used in IFT reduction. Many groups have paid more attention to the investigations of the phase behavior of the zwitterionic IL.27-34 Sun et al. synthesized a zwitterionic SAIL (3-(1-hexadecyl-3-imidazolio) propanesulfonate β-naphthalene sulfonate (C16IPS-Nsa)) and explored its abundant phase behavior in aqueous solutions (micelle, wormlike micelle, and hexagonal liquid crystals).34 The hydrophobic β-naphthalene sulfonate in the zwitterionic SAIL molecule played the significant roles in complex phase behavior. 2
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According to the Winsor’s R-ratio theory,35 the optimal surfactant structure for the interfacial adsorption consists of a large hydrophobic group and a corresponding hydrophilic head group. In general, the increased hydrophobicity is beneficial to the enhanced ability of the surfactant in IFT reduction.13 The increase of alkyl chain length may cause the precipitation or crystallization of surfactant molecules in aqueous solutions. Cui’s group synthesized zwitterionic surfactants with double long alkyl chains to increase the surfactant hydrophobicity.13,36,37 Another feasible route is to introduce a large hydrophobic group to the surfactant structure, which may decrease the synthetic steps and cost.38-39 Herein, we attempt to introduce two zwitterionic SAILs, C16IPS and C16IPS-Nsa, for chemical EOR. The interfacial activities of the two zwitterionic SAILs were evaluated by reducing the IFT of water/crude oil. The dynamic IFT and the salt and temperature effects were further investigated to verify the action mechanism. In addition, the zwitterionic SAIL systems exhibited a satisfactory displacement performance in core flooding tests. 2. Experimental section 2.1. Chemicals Two zwitterionic SAILs, 3-(1-hexadecyl-3-imidazolio) propanesulfonate (C16IPS, Fig. 1a) and 3-(1-hexadecyl-3-imidazolio) propanesulfonate β-naphthalene sulfonate (C16IPS-Nsa, Fig. 1b) as well as 1-hexadecyl-3-methylimidazolium bromide (C16mimBr) and N-hexadecyl-N-methylpyrrolidinium bromide (C16MPB) were synthesized according to previous reports.29,34,40 The product purities were examined by
1
H nuclear magnetic resonance spectroscopy with a Bruker Avance 300
spectrometer. Toluene (>99 wt%), n-decane (>99 wt%), sodium chloride (>99 wt%), and other inorganic salts were purchased from Aladdin Chemical Reagent Company. All chemicals were analytical grade and used as received. The crude oil was obtained from the Jidong oilfield. The main composition and properties of the crude oil are shown in Table 1. The composition of the formation brine is given in Table 2. 2.2. Measurement of interfacial tension The interfacial tensions between the model oil (or crude oil) and the surfactant 3
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solutions were directly measured via the spinning drop method on a TX-500C spinning drop interfacial tension apparatus (American CNG Company) as in our previous report.39 Firstly, the surfactant aqueous solutions were sufficiently mixed via the stir and ultrasonic wave. The samples were kept unstirred for 24 h to dissolve adequately and then added to the glass tube. A droplet of model oil (or crude oil) was injected into the centre of the water phase. The interfacial tension was measured at a fixed rotating velocity (5000 rpm) at the given temperature. The final value was stable for at least 5 min and all of the values were measured at least three times. Finally, the average value was calculated to obtain the final value. 2.3. Core flooding tests The artificial core used for the flooding test was 5.0 cm in diameter, with a length of 60 cm, and was from a sandstone reservoir. The core was water wet. Its porosity was approximately 30–37% and its absolute permeability was ~500 mD. The core’s flooding test was performed at 30 °C, as follows. First, the core was saturated using brine, followed by the injection of crude oil until no more brine was produced (brine cut
