Experimental investigation of enhancement of carbon dioxide foam stability, pore plugging, and oil recovery in the presence of silica nanoparticles
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The influence of surface-modified silica (SiO2) nanoparticles on the stability and pore plugging properties of foams in porous media was investigated in this study. The pore plugging ability of foams was estimated from the pressure drop induced during foam propagation in porous media. The results clearly showed that the modified SiO2 nanoparticle-stabilized foam exhibited high stability, and the differential pressure increased in porous media by as much as three times. The addition of SiO2 nanoparticles to the foaming dispersions further mitigated the adverse effect of oil toward the foam pore plugging ability. Consequently, the oil recovery increased in the presence of nanoparticles by approximately 15% during the enhanced oil recovery experiment. The study suggested that the addition of surface-modified silica nanoparticles to the surfactant solution could considerably improve the conventional foam stability and pore plugging performance in porous media.
KeywordsFoam Pore plugging Surface-modified nanoparticle Enhanced oil recovery
Gas injection involves the injection of carbon dioxide, methane, and nitrogen and other agents to dissolve and mobilize hydrocarbon components of crude oil (Orr 2005; Rossen and Bruining 2007; van Batenburg et al. 2010). Unfortunately, injection of steam or gas (carbon dioxide, nitrogen, and natural gas) into a reservoir results in a poor sweep efficiency (Rossen and van Duijn 2004; Farajzadeh et al. 2012). Gas injection also suffers from channeling, viscous fingering, and gravity overrides due to the reservoir heterogeneity and its low viscosity and density compared with the resident oil in the reservoir. The less viscous gases have a greater tendency to finger through the existing high-permeability channel pathways or to rise to the top of the reservoir as a result of gravity override, resulting in premature gas breakthrough (Apaydin and Kovscek 2001; Pal et al. 2017). Hence, the concept of mobility control was proposed in order to mitigate gas fingering and gravity override (Yang and Reed 1989; Kharrat and Mahdavi 2012).
Foam flooding was introduced as an effective method to reduce the injected gas mobility (Bond and Holbrook 1958), especially carbon dioxide foam, due to the achievable miscibility and greenhouse gas control (Li et al. 2016). Improvement in oil recovery due to high apparent viscosity and favorable flow behavior of foams in porous media has been reported in the results of previous studies (Rossen and Bruining 2007; Andrianov et al. 2012; Pal et al. 2017). Due to a significant reduction in gas and injected water mobility, the fluids were diverted from high-permeability zones to low-permeability upswept zones during the conventional foam (surfactant-stabilized foam) flow in porous media (Wang 1984; Alkan et al. 1991; Kim et al. 2005; Ashoori et al. 2012; Farzaneh and Sohrabi 2013). However, surfactant-stabilized foams are kinetically unstable and coalesce easily in porous media, especially in the presence of oil and in high-salinity and high-temperature environments (Bernard and Holm 1964; Kornev et al. 1999; Alargova et al. 2004; Rodriguez et al. 2007; Hunter et al. 2008). Consequently, a surfactant–silica nanoparticle combination has been recently introduced in order to generate durable foams and to address the limitations of the conventional surfactant-stabilized foams (Binks and Fletcher 2001; Binks 2002; Fujii et al. 2006; Hunter et al. 2009; Yekeen, et al. 2017a).
Theoretically, foam stabilization by nanoparticle–surfactant mixtures strongly depends on the properties of the nanoparticles, nanoparticle aggregation at the foam lamella, surfactant types, and the presence of the oil phase in the system. Particle hydrophobicity has been acknowledged as one of the critical factors influencing the stability of nanoparticle-stabilized foams. Results of previous studies show that super-stable foams were produced by partially hydrophobic nanoparticles of contact angles within the range of 60° to 100° (Marinova et al. 2002; Alargova et al. 2004; Binks and Horozov 2005; Kruglyakov et al. 2011; Yekeen et al. 2017b).
Dickinson et al. (2004) found that large yield stress of gel-like layer was formed by the adsorption and aggregation of partially hydrophobized silica nanoparticles at the foam lamellae which stabilized the generated foam. The nanoparticles further reduced the antifoam influence of oil by impeding the oil spreading at the gas–liquid interface of the foam. Binks and Horozov (2005) used fumed silica nanoparticles which have been hydrophobized to different extents using dichlorodimethylsilane. They found that the surface pressure of the foam reached a maximum value for silica nanoparticles with contact angles of 80°–90°. The improved stability of the foam in the presence of nanoparticles was attributed to the effective attachment of nanoparticles at the foam interface. Yekeen et al. (2017b) provided a comparison between the foam stabilized by hydrophilic silica and 50% methylsilyl-capped silica nanoparticles. They found that the moderately hydrophobic silica nanoparticle-stabilized foam was the most stable foam due to their thicker lamellae. The adsorption and accumulation of nanoparticles at the gas–liquid interface of the foam improved the static and dynamic stability of foam in porous media.
ShamsiJazeyi et al. (2014) studied the effect of polymer-modified silica nanoparticles on foam flow in the Boise sandstone and found that the presence of partially hydrophobic polymer-modified silica nanoparticles increased the flow pressure drop. The flow of nanoparticle-stabilized foam was modeled accounting for the nanoparticle/surfactant concentration ratio as part of the parameters (Worthen et al. 2015). The model predictions demonstrated the effectiveness of the pore plugging and fluid diversion by nanoparticle-stabilized foam. Some practical challenges of the nanoparticle-stabilized foam in field applications are the requirement of the high threshold shear rate for foam generation and nanoparticle agglomeration on pore spaces.
Partially hydrophobic silica nanoparticles are scarce because silica nanoparticles exist mainly as hydrophilic. Normally, to achieve the condition where silica nanoparticles can be termed as partially hydrophobic, the particles need to undergo surface wettability alteration. This can be done through surfactant adsorption where the particles are dispersed in a surfactant solution (Tiberg et al. 1999; Zhang and Somasundaran 2006; Zhang et al. 2008; Hunter et al. 2009; Carn et al. 2009; Cui et al. 2010; Fischer et al. 2012) or chemical modification (ligand exchange) on particle surfaces (Binks 2002; Dickinson et al. 2004; Kostakis et al. 2006; Rahman and Padavettan 2012; Wang et al. 2014). Despite some reported studies of the stability of nanoparticle-stabilized foams, the effects of surface-modified silica nanoparticles on dynamic foam stability and pore blocking performance in porous media are not yet understood. Most of the recent studies have been limited to bulk foam stability. Therefore, the objective of this research is to experimentally determine the effects of surface-modified silica nanoparticles on static and dynamic stabilities of conventional foams, and their pore blocking properties for EOR applications.
Sodium dodecyl sulfate (SDS) is widely used as anionic surfactant. It was purchased from Scharlau Chemie (analytical grade, purity > 99%). In this study, a 0.4 wt% SDS solution was used [above the critical micelle concentration (CMC)].
Non-treated bare silica dioxide (SiO2) nanoparticles (surface hydrolyzed to 100% Si-OH, purity > 99.5%) and two surface-modified SiO2 nanoparticles, Silica A (surface hydrolyzed to 60% Si-OH, purity > 96.3%) and Silica B (surface hydrolyzed to 40%, purity > 95.9%), were all purchased from US Research Nanomaterials Inc. Silica A and Silica B were modified with different degrees of γ-aminopropyltriethoxysilane (APTES), resulting in different wettability depending on the hydrolyzed surface.
Phytagel, polysaccharide gellant (used as a gelling agent), and polydimethylsiloxane (PDMS) were purchased from Sigma-Aldrich. Paraffin oil was supplied by QReC Asia with a viscosity of 24 cP and a density of 0.85 g/cm3 at 25 °C. n-decane (analytical grade) was provided by MERCK Group with a density of 0.73 g/cm3 and a viscosity of less than 3 cP at 25 °C. Carbon dioxide (CO2, purity > 96%) was supplied by Mega Mount Industrial Gases Sdn Bhd. All reagents were used without further purification.
Deionized water was used to prepare all solutions. The density, viscosity, and pH of deionized water were 1.0 g/cm3, 1.0 cP, and 7, respectively.
2.2 Experimental methods
2.2.1 Silica nanoparticle hydrophobicity
The SDS/silica nanoparticle solution was prepared by mixing silica with deionized water and later stirring at 2000 rpm to ensure homogeneous dispersion before the addition of SDS. The 0.4 wt% SDS solution was then added to the homogeneous silica dispersion, and the dispersion was shaken at a low rate of 10–20 rpm for 12 h to ensure homogeneity of the solution without producing foam.
The contact angle of SiO2 nanoparticles at the air–water interface was measured through the combination of gel trapping technique (GTT) and atomic force microscopy (AFM) proposed by Arnaudov et al. (2010). The detailed experimental procedures are as follows:
Static sessile drop shape analysis was also conducted by dropping a drop of the SDS solution on the prepared SiO2 nanoparticle sheet using a microsyringe. The drop shape was captured using a high-resolution camera Nikon D90 and Nikkor Micro Lens 60 mm.
2.2.2 Bulk stability of SDS/silica foams
Static bulk foam stability was measured by using a 50-cm-long graduated foam column. Fifty milliliters of sample solution was poured slowly into the cylinder. CO2 gas was injected at a flow rate of 0.05 mL/s through the pores (10–16 mm) in the sintered disk which was attached to the bottom of the cylinder. Foam was generated for 5 min, and the initial foam height was recorded after generation. Foam height was recorded for the duration of 20 min after generation. The 0.4 wt% SDS solution, above the CMC value (0.23 wt%), was used to aid the attachment of SiO2 nanoparticles at the foam interface by lowering the surface tension to its minimum value.
2.2.3 Pore plugging ability of SDS/silica foams
2.2.4 Application of SDS/silica foams in enhanced oil recovery
A glass-bead pack of porosity 0.34 and permeability 1.9 D (pore volume, 77 mL) was used, replacing the earlier glass-bead pack and assembled with the other apparatus as shown in Fig. 1. Initially, the glass-bead pack was preconditioned with 1.5 PV brine (salinity 30,000 ppm) injection. The brine was injected at a flow rate of 0.5 mL/min with a constant back pressure of 10 psi. Following the brine saturation, paraffin oil was injected at a flow rate of 0.5 mL/min until the oil cut reached 98%. Irreducible water saturation and initial oil saturation were estimated. Later, the fully oil-saturated glass-bead pack was reduced to residual oil through waterflooding. 1.2 PV of brine was injected at a flow rate of 0.5 mL/min under a pressure drop of 2 psi. The residual oil saturation was calculated.
Gas flooding was started with an injection of carbon dioxide gas at a flow rate of 3.0 mL/min under a pressure drop of 2 psi. The oil produced was carefully collected and measured and the gas injection was halted when significant oil production had ceased. The detailed experimental procedures are as follows: Foam flooding for residual oil was started after the glass-bead pack was waterflooded and oil saturation was reduced to residual oil saturation. 0.2 PV of SDS solution was injected at a flow rate of 0.5 mL/min. The purpose of the SDS solution injection was to mitigate the escaped carbon dioxide gas during pre-generated foam injection. 0.2 PV of pre-generated SDS foam was later injected at a flow rate of 0.05 mL/s. Subsequently, 0.6 PV of carbon dioxide gas was injected at a flow rate of 3.0 mL/min under 2 psi pressure drop. The SDS solution and pre-generated SDS foam were resupplied after 0.6 PV of carbon dioxide gas had been injected. The foam flooding was halted when no further significant oil production was observed. The exact procedure was repeated for SDS/Silica A and SDS/Silica B. The produced oil was collected, and recovery result was calculated and compared to determine foam flooding effectiveness.
3 Results and discussion
3.1 Contact angle of silica nanoparticles at foam interface
Properties of silica nanoparticles
Appearance and purity
Contact angle, degree
Range of detachment energy, kT
Static sessile drop
Static sessile drop
White powder, spherical, 99.5% purity, hydrophilic
White powder, spherical, 96.3% purity, weak hydrophilic
White powder, spherical, 95.9% purity, hydrophobic
3.2 Effect of surface-modified silica nanoparticles on static stability of SDS/silica foam
Foam stabilized by bare silica (SDS/bare silica) was less stable compared with foam stabilized by Silica A (SDS/Silica A) and Silica B (SDS/Silica B). Bare silica nanoparticles remained in the liquid phase due to their hydrophilicity, while weakly hydrophilic Silica A and hydrophobic Silica B nanoparticles resided firmly at the foam interface owing to their partial wettability. Better stability displayed by SiO2 nanoparticle-stabilized foam was attributed to the formation of a monolayer of bare SiO2 nanoparticles inside the liquid film and effective attachment of surface-modified SiO2 nanoparticles at the foam interface which had slowed down the liquid drainage (Lee et al. 2005; Horozov 2008; Yekeen et al. 2017a). In addition, the formation of a SiO2 nanoparticle monolayer provides electrostatic repulsion between two adjacent bubbles preventing them from coalescing (Hotze et al. 2010). However, continuous gravity-induced drainage eventually caused the destabilization of the formed monolayer, especially for SDS/bare silica foam. Due to their inability to withstand the hydrodynamic flow, the bare silica monolayer disintegrated and dragged away leaving blotches of uncovered foam film. The uncovered film is prone to rupture due to the increasing disjoining pressure previously hindered by the presence of electrostatic repulsion between silica particles. Conversely, the effective attachment of surface-modified SiO2 nanoparticles at the foam interface prevented the SiO2 nanoparticles from being dragged away by the liquid drainage. It further provided a prolonged steric barrier against coalescence and increasing surface elasticity, which is important in preventing foam coarsening (Yekeen et al. 2017a).
3.3 Influence of surface-modified silica nanoparticles on pore plugging ability of SDS/silica foam
3.4 Effect of oil viscosity on SDS/silica foam performance
3.5 SDS/silica foam flooding enhancement
From Fig. 12, the oil recovered by SDS/Silica A foam was higher than any other foam investigated. After waterflooding, 18% more of the residual oil was recovered by SDS/Silica A foam, with the ultimate oil recovery reaching 73%. Figure 13a further shows the effectiveness of SDS/Silica A foam where the higher oil production was maintained until 5 PV of gas injection. This was not achievable by gas flooding where the oil production was almost zero after 3.5 PV of gas was injected into the glass-bead pack. Utilization of surface-modified silica nanoparticles has produced high foam stability which can be observed in the increasing oil recovery. The more stable foam has a capability to last longer and to improve the sweep efficiency without collapsing while in contact with the residual oil. This is due to the presence of irreversibly attached surface-modified silica nanoparticles that prevent oil from spreading and providing steric hindrance from the oil anti-foaming properties (Marinova et al. 2002; Binks and Horozov 2005; Yekeen et al. 2017b). Consequently, effective foam flooding was achieved, increasing the ultimate oil recovery.
From the results of this study, it can be concluded that the addition of surface-modified silica nanoparticles has substantially boosted the conventional foam stability. Owing to the high detachment energy, the insoluble silica nanoparticles were irreversibly placed at the foam interface, thus providing enhanced foam stability. Improved foam stability was also indicated from the higher plugging pressure and more effective pore plugging performance compared with the conventional SDS foam. In addition, the presence of effectively attached surface-modified silica nanoparticles is capable of mitigating the adverse effect of oil making foam flooding a favorable choice for residual oil recovery. From the residual oil recovery results, it was conclusively found that the surface-modified silica nanoparticle-stabilized foam has a better performance, recovering up to 18% of the residual oil. Evidently, the addition of surface-modified silica nanoparticles boosted the static and dynamic foam stabilities.
The authors would like to thank the Ministry of Higher Education (Vot No. Q.J130000.2542.08H61) and Universiti Teknologi (UTM) Malaysia for supporting this research.
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