The Wettability Alteration and the Effect of Initial Rock Wettability on Oil Recovery in Surfactant-based Enhanced Oil Recovery Processes

Wettablity alteration of rock surface is an important mechanism for surfactant-based enhanced oil recovery (EOR) processes. Two salt and temperature-tolerant surfactant formulations were developed based on the conditions of high temperature (97–120°C) and high salinity (20 × 10⁴ mg/L) reservoirs where a surfactant-based EOR process is attempted. Both the two sufactant formulations can achieve ultralow interfacial tension level (≤10^?3 mN/m) with crude oil after aging for 125 days at reservoir conditions. Wettability alteration of core slices induced by the two surfactant formulations was evalutated by measuring contact angles. Core flooding experiments were carried out to study the influence of initial rock wettabilities on oil recovery in the crude oil/surfactant/formation water/rock system. The results indicated that the two formulations could turn oil-wet core slices into water-wet at 90–120°C and 20 × 10⁴ mg/L salinity, while the water-wet core slices retained their hydrophilic nature. The core flooding experiments showed that the water-wet cores could yield higher oil recovery compared with the oil-wet cores in water flooding, surfactant, and subsequent water flooding process. The two surfactant formulations could successfully yield additional oil recovery in both oil-wet and water-wet cores.     

Dynamics of capillary imbibition when surfactant, polymer, and hot water are used as aqueous phase for oil recovery

Capillary imbibition is an oil recovery mechanism in naturally fractured reservoirs if rock matrix is water wet and there is enough water in fractures in contact with matrix. It, however, may not yield an effective recovery under certain circumstances even if these conditions are maintained. Heavy matrix oil, high interfacial tension (IFT), oil-wet matrix sample, and limited contact area of matrix with water in fractures require additional effort to enhance the oil recovery by capillary imbibition. Chemicals and heat can be injected into naturally fractured reservoirs to improve the capillary imbibition recovery performance. With the involvement of low IFT fluid, heat, and polymer solution in the process, capillary imbibition dynamics may change and this entails an identification of the dynamics of the process through laboratory experiments before injection of these expensive fluids into oil reservoirs. In this study, the dynamics of capillary imbibition was studied experimentally. Static imbibition experiments were conducted on oil- and water-wet rock samples under different boundary conditions and saturated with different types of oil. The analyses were conducted using three indicators, namely the capillary imbibition rate, ultimate oil recovery, and shape of the recovery profile. Based on these indicators, the dynamics of capillary imbibition of different aqueous phases were evaluated for different oil types and matrix properties. The conditions that cause weak or strong capillary imbibition were identified.     

Parametric analysis of surfactant-aided imbibition in fractured carbonates

Many carbonate oil reservoirs are oil-wet and fractured; waterflood recovery is very low. Dilute surfactant solution injection into the fractures can improve oil production from the matrix by altering the wettability of the rock to a water-wetting state. A 2D, two-phase, multicomponent, finite-volume, fully-implicit numerical simulator calibrated with our laboratory results is used to assess the sensitivity of the process to wettability alteration, IFT reduction, oil viscosity, surfactant diffusivity, matrix block dimensions, and permeability heterogeneity. Capillarity drives the oil production at the early stage, but gravity is the major driving force afterwards. Surfactants which alter the wettability to a water-wet regime give higher recovery rates for higher IFT systems. Surfactants which cannot alter wettability give higher recovery for lower IFT systems. As the wettability alteration increases the rate of oil recovery increases. Recovery rate decreases with permeability significantly for a low tension system, but only mildly for high tension systems. Increasing the block dimensions and increasing oil viscosity decreases the rate of oil recovery and is in accordance with the scaling group for a gravity driven process. Heterogeneous layers in a porous medium can increase or decrease the rate of oil recovery depending on the permeability and the aspect ratio of the matrix block.     

Comparison of residual oil cluster size distribution, morphology and saturation in oil-wet and water-wet sandstone

We imaged an oil-wet sandstone at residual oil saturation (S(or)) conditions using X-ray micro-tomography with a nominal voxel size of (9 μm)(3) and monochromatic light from a synchrotron source. The sandstone was rendered oil-wet by ageing with a North Sea crude oil to represent a typical wettability encountered in hydrocarbon reservoirs. We measured a significantly lower S(or) for the oil-wet core (18.8%) than for an analogue water-wet core (35%). We analysed the residual oil cluster size distribution and find consistency with percolation theory that predicts a power-law cluster size distribution. We measure a power-law exponent τ=2.12 for the oil-wet core which is higher than τ for the water-wet system (τ=2.05), indicating fewer large clusters in the oil-wet case. The clusters are rough and sheet-like consistent with connectivity established through layers in the pore space and occupancy of the smaller pores; in contrast the clusters for water-wet media occupy the centres of the larger pores. These results imply less trapping of oil, but with a greater surface area for dissolution. In carbon storage applications, this suggests that in CO(2)-wet systems, capillary trapping is less significant, but that there is a large surface area for dissolution and reaction.     

Mechanisms of Enhanced Oil Recovery by Surfactant-Induced Wettability Alteration

Different measurements were conducted to study the mechanisms of enhanced oil recovery (EOR) by surfactant-induced wettability alteration. The adhesion work could be reduced by the surfactant-induced wettability alteration from oil-wet conditions to water-wet conditions. Surfactant-induced wettability alteration has a great effect on the relative permeabilities of oil and water. The relative permeability of the oil phase increases with the increase of the water-wetness of the solid surface. Seepage laws of oil and water are greatly affected by surfactant-induced wettability alteration. Water flows forward along the pore wall in the water-wet rocks and moves forward along the center of the pores in the oil-wet rocks during the surfactant flooding. For the intermediate-wet system, water uniformly moves forward and the contact angle between the oil–water interface and the pore surface is close to 90°. The direction of capillary force is consistent with the direction of water flooding for the water-wet surface. While for the oil-wet surface, the capillary force direction is opposite to the water-flooding direction. The highest oil recovery by water flooding is obtained at close to neutral wetting conditions and the minimal oil recovery occurs under oil-wet conditions.     

Study of Spontaneous Imbibition of Water by Oil-Wet Sandstone Cores Using Different Surfactants

The mechanism of spontaneous imbibition of water by sandstone cores and the relationship between reservoir wettability and imbibition recovery were studied by investigating factors influencing the spontaneous imbibition of different surfactants by oil-wet sandstone cores. Ultimate oil recovery of cores using the cationic surfactant CTAB was higher than that of the cores using the nonionic surfactant TX-100 and the anionic surfactant POE (1) at the same concentration. For CTAB and TX-100, the ultimate oil recovery by spontaneous imbibition increased with increase in surfactant concentration. In regard to imbibition recovery, TX-100 and POE(1) at high temperatures were superior to those at low temperatures. Ultimate oil recovery of the high-permeability core was higher than that of the low-permeability core at room temperature. According to changes in the driving force during the imbibition process, the imbibition curve could be divided into three regions: (1) mainly capillary force, (2) both capillary and gravity forces, and (3) mainly gravity force. The stronger the hydrophilicity of the rock surface, the higher the spontaneous imbibition recovery.     

Ionic liquids enhanced oil recovery from oily sludge-experiment and mechanism

The oily sludge would cause environment pollution, and would cause the heavy oil waste. Therefore, it was vital for us to find novel methods to obtain heavy oil from the oily sludges. In this study, the [C₁₂mim][PF₆] and [C₁₂mim][Br] ionic liquids(ILs) were used to enhance the oil recovery. The toluene could obtain the highest oil recovery, and both the two ILs could increase the oil recovery. Toluene could obtain the highest oil recovery (89.4 wt%), and n-octane could obtain the lowest oil recovery (76.8 wt%). [C₁₂mim] [PF₆] could efficiently increase the heavy oil recovery to 91.2 wt%(by toluene). The [C₁₂mim][Br] could increase the heavy oil recovery further. Both the [C₁₂mim] [PF₆] and the [C₁₂mim][Br] ionic liquids could increase the heavy ois C/H ratio, decrease heavy oil viscosity and increase the sands hydrophilicity. The [C₁₂mim][Br] ionic liquids showed better effect. In addition, the ionic liquids could increase the solvents recovery, and the ionic liquids recovery were high. Therefore, the ionic liquids enhanced oil recovery could be recycled to ten times. The two ionic liquids could effectively decrease the heavy oil interaction force, and when the ionic liquids increased to 200 ppm, the force remained stable. In the end, the ionic liquids enhancing solvent extraction mechanism was put forward.     

Spontaneous imbibition of surfactant solution into an oil-wet capillary: wettability restoration by surfactant-contaminant complexation

For a given type of rock, the effectiveness of oil recovery through wettability alteration is highly dependent upon the nature of the water-soluble surfactant used. Different mechanisms have been proposed by others to explain wettability alteration by surfactants, and understanding the process is crucial to improve recovery performance. Known mechanisms include (1) surfactant adsorption onto the oil-wet solid surface (coating mechanism) and (2) surfactant molecules complexing with contaminant molecules from the crude oil which are adsorbed on the rock surface so as to strip them off (cleaning mechanism). With the second mechanism, the wettability is restored by lifting the contaminant layer away, exposing the rock surface which was originally water-wet. We previously focused on the numerical modeling of the surfactant coating mechanism (Hammond and Unsal Langmuir2009, 25, 12591; 2010, 26, 6206), and we now present a numerical study for the cleaning process. Our new model shows that when a wettability altering surfactant solution is allowed to imbibe spontaneously and acts by the cleaning process, the meniscus advances more rapidly than when there was wettability alteration by coating alone. In our previous model there was a concentration threshold below which imbibition was not possible. That threshold arose because a finite amount of surfactant needs to be adsorbed onto the oil-wet surface to change the contact angle to a water-wet value, but the maximum amount that can be absorbed is limited by the requirement that it be in equilibrium with the surfactant concentration near the meniscus. In the new model, with the cleaning mechanism there is no such threshold, since the cleaning process is driven by the surfactant flux into the vicinity of the advancing meniscus rather than the surfactant concentration there. As long as there are surfactant molecules present in the aqueous solution, the flux is nonzero and molecule pairs can form and alter the wettability by removing the contaminant from the oil-wet surface. However, under very low surfactant concentrations, the process is extremely slow compared to at higher concentrations.     

Structural,thermal, optical and conductivity studies of Co/ZnO nanoparticles doped CMC polymer for solid state battery applications

In this study, a simple chemical precipitation method was used to synthesize ZnO: Co²⁺ as nanoparticles. The solution casting technique was used for the preparation of polymer films of Carboxymethyl cellulose (CMC) doped with different contents (0.5, 1.5, 3, and 5 wt%) of ZnO/Co NPs. As shown by the X-ray diffraction, the average size of ZnO/Co crystallite of the NPs is 25.6 nm. Meanwhile, the addition of ZnO/Co reduced the semi-crystallinity of CMC. The Fourier transform infrared (FTIR) confirmed the interaction between the ZnO/Co NPs and the polymer CMC. The direct and indirect band gap (Eg) was reduced from (5.32–5.01 eV and 5.20 to 4.99 eV respectively) with the increase in ZnO/Co NPs content up to 3 wt% after this content the Eg is increased as shown by the UV–Vis spectra. In addition, the results of TGA displayed the decomposition of the nanocomposite to be little compared to that of the pure CMC indicating the success of fabrication of products. The improvement of the ionic conductivity was noticed upon the addition of ZnO/Co NPs into the polymer CMC system which can be explained in terms of an increase in amorphicity as shown by the impedance spectroscopic study. It was found that the optimum ionic conductivity (3.209 × 10⁻⁶ Scm⁻¹) at ambient temperature was higher for the sample containing 1.5 wt% ZnO/Co NPs with highest of amorphicity and the lowest total loss of weight. Therefore, the improvements in optical properties, thermal stability, and AC conductivity which were observed represent a strong support for the use of the nanocomposite films in the solid state battery applications.     

Application of response surface methodology for optimization of the stability of asphaltene particles in crude oil by TiO2/SiO2 nanofluids under static and dynamic conditions

In this work, the onset of asphaltene flocculation for an Iranian crude oil by titration of samples with heptane in the presence and absence of the TiO₂/SiO₂ nanofluids was obtained by Near-IR spectroscopy. Nanoparticles and nanocomposites were characterized by BET, FESEM, EDX, XRD, and XRF analysis. Modeling and optimization of inhibition of asphaltene flocculation process by TiO₂/SiO₂ nanofluids were conducted by response surface methodology (RSM). Under optimum conditions (nanocomposite composition = 0.04 wt% (80%TiO₂:20%SiO₂), salinity = 4.01 wt%, and pH = 3.42), the onset point increased. For nanofluids stability analysis, the optimum nanofluid was compared with the two other nanofluids (SiO₂ and TiO₂) by visual observation method. The results indicated that high stability and surface area of the 80%TiO₂ nanocomposites increase asphaltene adsorption on the particles surface that subsequently increases the onset point. In addition, the optimum nanofluid performance on the carbonate rocks was evaluated by contact angle and core flooding experiments. The 80% TiO₂ nanofluid changed the wettability of carbonate rocks from strongly oil-wet to strongly water-wet condition and also decreased the residual oil saturation and enhanced the oil recovery with an increase in the recovery factor of about 15%.     

Selection of natural fibers based brake friction composites using hybrid ELECTRE-entropy optimization technique

Selecting the best brake friction composite composition amongst a set of natural fibres reinforced composites using hybrid optimization method - ELECTRE (elimination and choice translating priority) II - entropy is discussed in this article. Three sets of natural fibres containing different amounts of banana, hemp, and pineapple reinforced brake friction composites were tested according to IS 2742 (part-4) regulations on a chase friction testing machine. The experimental results have been discussed in terms of seven performance defining attributes such as coefficient of friction, fade, wear, friction stability coefficient, friction recovery, friction fluctuations, and friction variability coefficient. The composite containing 5 wt% pineapple fiber exhibit the highest coefficient of friction, whereas wear performance and friction stability remain highest for 5 wt% hemp fiber based composites. The recovery performance remains highest for the composite containing 15 wt% banana fiber, while fade, friction variability, and fluctuations remain lowest for 10 wt% banana fiber reinforced composites. The tribological results indicate that the inclusion of disparate natural fibers in varying amounts may differently affect the tribological performances and therefore to choose the best brake friction composite satisfying the maximum beneficial criteria hybrid ELECTRE II- entropy optimization technique is used. Brake friction composite containing ~10 wt% banana fibers was ranked first, in meeting the desired performance tribological properties. A comparison of this optimization approach with other multi-criteria decision-making techniques is also made for validating the performance ranking of these composites.     

Significantly enhanced electromagnetic interference shielding effectiveness of montmorillonite nanoclay and copper oxide nanoparticles based polyvinylchloride nanocomposites

In the present study, montmorillonite (MMT) nanoclay and copper oxide (CuO) nanoparticles (NPs) reinforced polyvinylchloride (PVC) based flexible nanocomposite films were prepared via solvent casting technique. Using Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Scanning electron microscopy (SEM) and thermo-gravimetric analysis (TGA), the structural, morphological and thermal properties of PVC/MMT/CuO nanocomposite films with various loadings of CuO NPs and MMT were investigated. These studies suggested that by the addition of dual nanofillers in the polymer matrix some structural modifications occurred owing to the homogenous dispersion of MMT and CuO NPs within the PVC matrix. The TGA results reveal that the addition of CuO NPs and MMT considerably improved the thermal stability of the nanocomposites. The EMI shielding effectiveness (SE) of nanocomposites was examined in the X-band (8–12 GHz) and Ku-band (12–18 GHz) frequency regions. The EMI SE values were found to be −30 dB (X-band) and −35 dB (Ku-band) for nanocomposites containing 0.3 wt% of CuO NPs and 4.7 wt% of MMT respectively while the shielding was found to be absorption dominant. These results emphasize that PVC/MMT/CuO nanocomposite films can be used as a potential EMI shielding material.     

Optimization of Algerian rosemary essential oil extraction yield by supercritical CO2 using response surface methodology

The present study deals with the determination of optimal values of operating parameters such as temperature and pressure leading to the best yield of a supercritical CO₂ extraction of essential oil from local rosemary plants, using the response surface methodology (RSM). The maximum of essential oil recovery percentage relative to the initial mass of leaf powder was 3.52 wt%, and was obtained at 313 K and 22 MPa.A second-order polynomial was used to express the oil recovery and the calculated mass of recovered oil using the RSM was very close to the experimental value, confirming the reliability of this technique.The chemical composition of the Algerian rosemary oil under the obtained optimal conditions (313 K and 22 MPa), determined by GC–MS analysis, revealed the presence of camphor (major compound) (52.12%), 1,8-cineole (9.65%), camphene (7.55%), α-pinene (6.05%), borneol (3.52%), aroma dendrene (2.11%), verbenone (1.97%), α-caryophyllene (1.71%), and others.     

Multi-parameter screening study on the static properties of nanoparticle-stabilized CO2 foam near the CO2 critical point

The important role of nanoparticles (NPs) on foam stabilization under harsh geological conditions has been well recognized. In this paper, the Orthogonal Experimental Design (OED) method is adopted to investigate the synergy effects of six parameters, including NP concentration, surfactant concentration, oil concentration, salinity, temperature, and pressure, under five levels in the range of 0–0.2 wt%, 0.1–0.5 wt%, 0–4 wt%, 0–8 wt%, 20–60 °C, and 5.5–9.5 MPa respectively. K values and B values obtained in the OED experiments are employed to show the single parameter effect and the importance of each influential factor on foam static properties. It is concluded that system temperature and pressure, which has the highest B values of 22 mm and 18 mm on foam height results, are the dominant parameters on foamability, whereas temperature with B values of 80% on foam decay rate is the dominant factor on foam stability. It is observed when the system condition is close to the CO₂ critical point, the foamability and stability of the NP-stabilized foam are much worse than under conditions far from the critical point. At last, optimal formulation of surfactant and NP concentration is proposed and validated for two geological cases of 45 °C and 55 °C with salinity and oil presence. It is expected the experimental technique, as well as the research results, reported in this paper could help the laboratory screening and formulation optimization of the complex NP-stabilized ScCO₂ foam system.     

Ultrasonic treatment as recent and environmentally friendly route for the synthesis and characterization of polymer nanocomposite having PVA and biosafe BSA‐modified ZnO nanoparticles

The present study deals with the immobilization of ZnO nanoparticles (NPs) as nanofiller inside poly(vinyl alcohol) (PVA) by solution casting method which is a low‐cost, environmental‐friendly, and rapid method of sonochemistry. Firstly, the surface of ZnO NPs was treated by bovine serum albumin (BSA) in the phosphate‐buffered solution under ultrasonic cavitation. Three diverse polymeric nanocomposites (NCs) are formed by changing the percentage of ZnO@BSA NPs (3, 6, and 9 wt%) with same amount of PVA. The structure properties, morphology, and thermal stability of prepared NCs were determined through Fourier transform‐infrared spectroscopy, X‐ray diffraction, energy‐dispersive X‐ray spectroscopy (EDX) and optical UV‐Visible spectrum, transmission electron microscopy (TEM), and field emission scanning electron microscopy. The presence and the dispersal of the ZnO@BSA NPs in the PVA matrix were recognized by TEM. In the X‐ray diffraction analysis, the values of mean particle size using Debye‐Scherrer equation were estimated in the range 4 to 6 nm that is almost in agreement with TEM analysis. Increase of 14% in thermal stability and also increase of more than 2‐fold of the tensile strength of PVA/ZnO@BSA NC 9 wt% in respect to the pure PVA showed that the modified NPs well dispersed within PVA and attached to it.     

Preparation and Characterization of Fe3O4/Ethiodized‐oil Magnetic Fluids Used in Arterial Embolization Hyperthermia

Fe₃O₄ nanoparticles (NPs) were prepared by the co‐precipitation of Fe³⁺ and Fe²⁺ with ammonium hydroxide, and were modified by four different surfactants. The modified Fe₃O₄ NPs were characterized by Fourier transform infrared spectroscopy, X‐ray powder diffraction, transmission electron microscopy and vibrating sample magnetometer. Then, the modified Fe₃O₄ NPs were dispersed in ethiodized‐oil by mechanical agitation and ultrasonic vibration to obtain stable Fe₃O₄/ethiodized‐oil magnetic fluids (MFs). The magnetic properties and rheological properties of the MFs were measured using a Gouy magnetic balance and a rotational rheometer, respectively. The saturation magnetization of the Fe₃O₄ modified by oleic acid was 52.1 emu/g. Furthermore, the result showed that the inductive heating effect of oleic acid stabilized Fe₃O₄/ethiodized‐oil MF was remarkable and it only took 650 s for the temperature rising from 25°C to 65°C. The specific absorption rate of the MF was 50.16 W/(g of Fe). It had a potential application in arterial embolization hyperthermia.     

In situ sol–gel preparation of high transparent fluorinated polyimide/nano-MgO hybrid films

Hybrid nanocomposite films of magnesium oxide (MgO) in fluorinated polyimide (PI) from 4, 4′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) and 4, 4′-Diaminodiphenyl ether (ODA) have been successfully fabricated via an in situ sol–gel polymerization technique. The MgO content in hybrid films was varied from 0 to 5 wt%. The hybrid films were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), ultraviolet–visible (UV–Vis) spectroscopy and thermal gravimetric analyses (TGA). The results of FTIR, XRD and FESEM showed that the MgO nanoparticles were well dispersed in the polymer matrix due to the coordination between the carbonyl group of polymers and Mg atom, and the as-prepared hybrid films exhibited excellent optical transparency in the visible region and good UV-shielding properties in the UV region. Although the thermal stability of the hybrid films is slight inferior to pure PI, it is still good for the practical application below the temperature of 300 °C.     

Physico-chemical control over the single- or double-wall structure of aluminogermanate imogolite-like nanotubes

It is known that silicon can be successfully replaced by germanium atoms in the synthesis of imogolite nanotubes, leading to shorter and larger AlGe nanotubes. Beside the change in morphology, two characteristics of the AlGe nanotube synthesis were recently discovered. AlGe imogolite nanotubes can be synthesized at much higher concentrations than AlSi imogolite. AlGe imogolite exists in the form of both single-walled (SW) and double-walled (DW) nanotubes, whereas DW AlSi imogolites have never been observed. In this article, we give details on the physicochemical control over the SW or DW AlGe imogolite structure. For some conditions, an almost 100% yield of SW or DW nanotubes is demonstrated. We propose a model for the formation of SW or DW AlGe imogolite, which also explains why DW AlSi imogolites or higher wall numbers for AlGe imogolite are not likely to be formed.     

Synthesis method-dependent photothermal effects of colloidal solutions of platinum nanoparticles used in photothermal anticancer therapy

One of the most common anticancer therapies is photothermal therapy (PTT). The effectiveness of PTT depends on the photosensitizer being a molecule which is toxic for the cancer cells after electromagnetic wave irradiation. Therefore, a simulation of PTT was performed in this work on two colon cancer cells (SW480 and SW620) using platinum nanoparticles (Pt NPs). Interestingly, in the literature the dependence between the synthesis method and the photothermal properties of Pt NPs was not discussed. Consequently, in this paper, we evaluated the photothermal properties of Pt NPs synthesized by two different methods: polyol (PtI NPs) and green chemistry (PtII NPs). Scanning transmission electron microscopy revealed that the size of both Pt NPs obtained was 2 nm, the NPs were not agglomerated, and that the PtII NPs were distributed on green tea supports. The selected area electron diffraction and X-ray diffraction analysis confirmed the crystallinity of both types of Pt NPs. Fourier-transform infrared (FTIR) spectrum of the PtII NPs showed interactions between the NPs and stretching modes for C=O groups from flavonoids and polyphenols. Therefore, these chemical compounds could be responsible for reducing Pt⁴⁺ ions to Pt⁰. Moreover, the 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assay showed that the PtII NPs exhibited 10% and 20% better cytotoxicity effect on SW480 and SW620 cells, than PtI NPs. The viability of cancer cells decreased when Pt NPs were used in PTT. The highest percentage of dead cells (82%) was observed for PtII NPs and 650-nm laser irradiation. FTIR and Raman spectroscopy showed structural changes induced by both Pt NPs and laser irradiation of cells in the range corresponding to levels of DNA, phospholipids, proteins, and lipids. Moreover, the calculated photothermal conversion efficiency showed that the value of this parameter is around 35%, regardless of the synthesis method and used wavelengths.