No abstract

Anatase and amorphous TiO2 nanoparticles were used to improve recovery of heavy oil from sandstone cores. Before performing core floods, the stability of nanoparticles at different salinities was tested using ζ potential and ultraviolet–visible (UV–vis) methods. While water recovered only 49% of the oil in the core flood experiments, 0.01% anatase structure solution recovered 80% of the oil after injecting two pore volumes at optimum conditions. To understand the mechanism responsible for improved recovery, contact angle measurements were performed on the rock surface before and after treatment with the nanoparticle solution. Contact angle measurements showed that the rock wettability changed from oil-wet to water-wet conditions after treatment with nanoparticles. In 0.01% concentration, scanning electron microscopy (SEM) results showed homogeneous deposition of nanoparticles onto the core plug surface and a few nanorods with a diameter about 60 nm were observed. Energy-dispersive spectrometry (EDS) confirms diffusion of nanoparticles in porous media and uniform distribution. When the nanoparticle concentration was increased, more nanorods with the same diameter were composed, which resulted in plugging to occur. These results indicated the possibility of TiO2 application in enhanced oil recovery (EOR); however, more investigation is required to overcome multi-nanoparticle deposition onto pores.

No abstract

Interfacial tension (IFT) as one of the main properties for efficient CO2 flooding planning in oil reservoirs depends strongly on pressure, temperature, and composition of the reservoir fluids. Therefore, it is important to measure this property at real reservoir conditions for successful field development plan. In this study, an axisymmetric drop shape analysis (ADSA) has been utilized to measure the equilibrium IFTs between crude oil and CO2 at different temperatures and pressures. Moreover, minimum miscibility pressures (MMP) and first-contact miscibility pressures (P max) of crude oil/CO2 systems at different temperatures are determined by applying the vanishing interfacial tension (VIT) technique. Besides, the effects of paraffins content and resin to asphaltene ratio of the crude oil on the IFT behavior are investigated. The results show that while the IFT has a decreasing trend with temperature at low pressures region, it has an increasing trend with temperature at high pressures. Also, MMP and P max were found to increase linearly with temperature. The results indicate that paraffin has a critical effect on the crude oil/CO2 IFT behavior. It was also found that the lower the ratio of resin-to-asphaltene is, the more is the possibility of asphaltene precipitation as determined by examining the IFT behavior of the solution. Moreover, the results verified that the higher is the molecular weight of heavier components of the crude oil, the higher are the MMP values obtained.

No abstract

No abstract

Oil recovery from carbonate reservoirs can be enhanced by altering the wettability from oil-wet toward water-wet state. Recently, silica nanoparticle (SNP) suspensions are considered as an attractive wettability alteration agent in enhanced oil recovery applications. However, their performance along with the underlying mechanism for wettability alteration in carbonate rocks is not well discussed. In this work, the ability of SNP suspensions, in the presence/absence of salt, to alter the wettability of oil-wet calcite substrates to a water-wet condition was investigated. In the first step, to ensure that the properties of nanofluids have not been changed during the tests, stability analysis was performed. Then, low concentration nanofluids were utilized, and transient as well as equilibrium behavior of wettability alteration process were analyzed through contact angle measurement. Moreover, a mechanism for a wettability alteration process was proposed and verified with different tools. Results showed that the SNP suspensions could effectively change the wetness of strongly oil-wet calcite to water wet (e.g., from 156° to 41.7° at 2000 mg/L nanofluid). This ability was enhanced by increasing concentration, time, and salinity. Two equations were proposed to predict the equilibrium and transient contact angles with a good agreement. Analyzing the transient behavior of the wettability alteration indicated that the rate constant increased from 0.0019 to 0.0021 h–1 with the increase in nanofluid concentration from 500 to 1000 mg/L. It was further increased to 0.0026 h–1 for 1000 mg/L in 0.05 M electrolyte solution. The partial release of carboxylate groups from the oil-wet calcite surface and their replacement with SNP was suggested to be the responsible mechanism for wettability alteration. Surface equilibria and interaction studies, Fourier transform infrared spectroscopy, and scanning electron microscopy provided verification in support of the proposed mechanism. The enhanced wettability alteration in the electrolyte media was attributed to the role of Na+ ions facilitating the adsorption and release of SNP and stearates, respectively. In addition, the presence of electrolyte favorably affected the position of the system’s equilibria.

It is well known that the oil recovery is affected by wettability of porous medium; however, the role of nanoparticles on wettability alteration of medium surfaces has remained a topic of debate in the literature. Furthermore, there is a little information of the way dispersed silica nanoparticles affect the oil recovery efficiency during polymer flooding, especially, when heavy oil is used. In this study, a series of injection experiments were performed in a five-spot glass micromodel after saturation with the heavy oil. Polyacrylamide solution and dispersed silica nanoparticles in polyacrylamide (DSNP) solution were used as injected fluids. The oil recovery as well as fluid distribution in the pores and throats was measured with analysis of continuously provided pictures during the experiments. Sessile drop method was used for measuring the contact angles of the glass surface at different states of wettability after coating by heavy oil, distilled water, dispersed silica nanoparticles in water (DSNW), polyacrylamide solution, and DSNP solution. The results showed that the silica nanoparticles caused enhanced oil recovery during polymer flooding by a factor of 10%. The distribution of DSNP solution during flooding tests in pores and throats showed strong water-wetting of the medium after flooding with this solution. The results of sessile drop experiments showed that coating with heavy oil, could make an oil-wet surface. Coating with distilled water and polymer solution could partially alter the wettability of surface to water-wet and coating with DSNW and DSNP could make a strongly water-wet surface.