Characterization and evaluation of a natural surfactant extracted from Soapwort plant for alkali-surfactant-polymer (ASP) slug injection into sandstone oil reservoirs
Graphical abstract
Introduction
Injecting chemical slug into oil reservoirs is known as an effective method of EOR. Injection of slugs containing surfactant, surfactant-alkaline and alkaline-surfactant-polymer are the most common types of this method [[1], [2], [3], [4]]. Each of the additives used in chemical slug improves the mechanisms of EOR, such as reducing IFT, wettability alteration and regulating the water-oil mobility ratio by changing the properties of the injection fluid [5,6]. The reduction of interfacial tension based on Eq. (1) affects capillary pressure. The water-oil mobility ratio is also controlled by increasing the injection phase viscosity by the polymer in ASP-slug based on Eq. (2) [7].where Pc is the capillary pressure, r represents the capillary radius, θ stands for the contact angle, M is the mobility ratio, k represents the relative permeability and μ stands for the viscosity.
Surfactant injection, especially as ASP-slug, has had successful field applications. For example, ASP injection in Sinopec Henan oilfield increased tertiary oil recovery by 14.6% [8]. ASP-flooding increased Daqing field oil production by 3.5 million tons [9]. The ASP injection program was conducted in Shengli oilfield, which increased oil recovery by about 16.8% [10]. Adjusting the concentration and selecting the right surfactant as the main component of a chemical slug are more important than other components. Surfactant is added to injectable water with the main purpose of reducing interfacial tension. The efficiency and stability of surfactants at reservoir conditions are not the same, so it is justifiable to perform EOR tests and measure the efficiency of surfactants before field operations. In recent years, research on the use of natural-based surfactants has increased. Features such as low cost, availability, and environmental friendliness could make researchers interested in studying and exploration of new resources to provide natural-based surfactants. For example, Babu et al. used Castor Oil to synthesize a surfactant and characterized it using FTIR. The surfactant synthesized from Castor Oil reduced interfacial traction to ultra-low values and altered quartz wettability to hydrophilicity [11]. Saxena et al. tested a surfactant synthesized from Mahua oil for optimization of the EOR parameters. They achieved an ultra-low IFT in the range of 10−2 mN/m, altering the wettability to hydrophilicity and a 20% increase in oil recovery in the surfactant-polymer slug injection process into sandstone reservoirs [12]. They also achieved an IFT of about 2.123 × 10−2 mN/m and increased oil recovery by 30% using a soap-nut based surfactant in combination with polymer and alkali [13]. Pal et al. reduced the amount of IFT to the range of 10−3 –10−2 by synthesizing a sunflower-based Gemini surfactant. The surfactant had suitable foaming behavior and emulsion stability [14]. They synthesized another surfactant from Coconut oil and achieved a similar result in IFT trends and increased oil recovery by about 20% using the surfactant flooding into a sand-pack [15]. Nowrouzi et al. synthesized an anionic surfactant from waste chicken fat and characterized it by FTIR and TGA. They examined the surfactant performance in reducing IFT, altering the wettability and foaming and emulsion behaviors of the surfactant at CMC. The IFT reduced to about 10−2, wettability of carbonate rock altered to water-wetting and the surfactant generated stable foam and emulsion. The oil recovery also increased by about 18% under ASP-slug injection into a carbonate plug [16]. Nowrouzi et al. also studied the effect of the saponin of Anabasis Setifera plant. The surfactant was characterized by FTIR, 1HNMR and TGA. The IFT and contact angle reduced to 1.066 mN/m and 56.5°, respectively and an increase of 15.4% in the tertiary oil recovery was achieved by surfactant flooding in carbonate reservoir [17]. Pordel Shahri et al. exanimated the aqueous extract of Zizyphus plant as a surfactant. The surfactant reduced kerosene-water IFT from 48 to 9 mN/m [18]. The powder extract of Zizyphus plant was used by Zendehboudi et al. in the kerosene-water IFT experiments. They showed a reduction of 22 mN/m in IFT [19]. The extract of some plants such as Mulberry Tree Leaves [20], Henna [21], Olive, Spistan and Prosopis [22], Matricaria chamomilla [23], Trigoonella Foenum-Graceum [24], Vitagnus [25] and Alfalfa [26] as surfactants were used by researchers, which had a similar result of Zizyphus plant extract in IFT reduction. Research on the natural base surfactants and the exploration of new sources for their extraction and production continues to address some of the challenges of using chemical surfactants such as high cost and sometimes environmental incompatibility. In this study, the natural surfactant extracted from the root of the Soapwort plant as a renewable source was studied. The study of the new surfactant and its application in EOR normally have a standard procedure including the preparation and synthesis, characterization, CMC measurement, water-oil IFT and wettability tests, determining the optimum salinity and finally the oil production test such as flooding test [17]. Fig. 1 shows the general sketch of the problem of this study. The natural surfactant was analyzed using Proton Nuclear Magnetic Resonance (1HNMR), Fourier-Transform Infrared Spectroscopy (FTIR) and Thermal Gravimetric Analysis (TGA) techniques and its application in EOR was tested by various experiments such as IFT test, contact angle test and ASP-slug injection into a sandstone plug. In previous studies, crude plant extracts were commonly used as surfactants. Crude extracts, in addition to saponin, contain impurities such as Tannins. Tannins fall into the category of coagulants and have no surface activity. This property increases the interfacial tension due to the inhibition of the surface activity of saponin molecules [17]. Lack of surface activity of Tannins and other impurities causes irregular adsorption at the liquid-liquid interface and breaks the interfacial tension trend against surfactant concentration. The novelty of this study, in addition to the introduction of Soapwort plant as a new and available source for extracting surfactant for use in ASP-slug injection in sandstone oil reservoirs, is the use of pure and modified saponin to improve EOR mechanisms compared to the use of crude plant extracts. The followings are the sections related to this experimental study. First, the experimental section is presented. This section includes the introduction of materials and a description of laboratory methods. The results are then displayed as tables and diagrams in separate sections, and the existing mechanisms are discussed. Finally, the most prominent results and suggestions based on the findings of this study are presented.
Section snippets
Materials
Sandstone sampled from the outcrop of Aghajari Formation in Iran was used as narrow sections and as plugs. The used sandstone contained 53% quartz, 15% feldspar and 29% iron oxide. Fig. 2 shows the XRD analysis of the sandstone. In the XRD curve, the peaks at 21.48°, 27.183°, 27.42°, 36.59°, 37.07°, 40.024°, 42.99°, 46.24°, 50.72°, 55.50°, 58.01°, 60.587°, 68.24°, 36.66°, 73.72°, 76.22° and 77.96° represent quartz, peaks at 15.47°, 27.183°, 30.032°, 35.35° and 37.07° represent feldspar and
Surfactant characterization
FTIR analysis was used to define the functional groups in the molecular structure of the surfactant extracted from Soapwort plant. Peaks at 3412 cm−1, 2936 cm−1, 1731 cm−1, 1610 cm−1 represent the –OH, CH, CO and CC bonds, respectively and peak at 1046 cm−1 indicates Oligosaccharide linkage absorptions to sapogenins. The links to the peaks shown in Fig. 3 indicate the functional groups in the saponin structure. The general molecular structure of saponins is shown in Fig. 4. The dual structure
Summary and conclusions
A non-ionic surfactant was extracted from Soapwort plant as a renewable resource. The use of the surfactant in EOR was investigated by performing various experiments after characterization. The main conclusions from this study are as follows:
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The CMC was obtained at 2250 ppm by surface tension experiments using the pendant drop method. Due to the low CMC of the surfactant, it can be considered economically viable.
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The water-oil IFT at CMC decreased by 0.832 mN/m. However, this value was reduced
CRediT authorship contribution statement
Iman Nowrouzi: Conceptualization, Methodology, Investigation, Validation, Writing - original draft. Amir H. Mohammadi: Supervision, Writing - review & editing. Abbas Khaksar Manshad: Supervision, Writing - review & editing.
Declaration of competing interest
The authors declare that they have no conflict of interest in this work.
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