We report new experimental data on concentration-dependent molecular diffusion coefficient of ethane in toluene at temperatures ranging from 21 to 125 C and pressures up to 4.14 MPa. An analytical model has also been developed for estimation of the diffusion coefficient utilizing the experimental data of the interface velocity as a result of swelling and the rate of gas dissolution in the liquid phase. It is shown that the diffusion coefficient of ethane in toluene is dependent on the initial mass fraction of the gaseous component in the liquid. In addition, the effect of concentration dependency of the molecular diffusion coefficient on diffusive mass flux is quantified.The results reveal that the assumption of a constant diffusion coefficient introduces 10-60% error in calculation of diffusional mass transfer flux. The developed methodology finds application in estimation of the concentration-dependent molecular diffusion coefficient of gases in liquids.
The IFT and contact angle are believed to have direct impact on wettability alteration of crude oil/water/rock systems. In this work, extensive laboratory work was conducted to investigate the effect of these two key parameters on wettability alteration at elevated temperature (90°C) and ambient conditions. Twenty-six brines representing various scenarios of dilution and sulphate spiking were prepared and tested to identify the smart water most effective in the alteration of wettability. Sea water (SW) was used a base brine. Diluted and sulphate-spiked versions of SW were synthetically prepared following the standard brine preparation procedures. Also standard procedures were followed for the measurement of IFT and contact angle measurements using Teclis tracker. Pendant drop method was implemented to measure the IFT at ambient and 90°C conditions using a special software package that adopts the axisymmetric drop shape analysis and fits the Laplace equation. The same software package was used to take snapshots of oil drops at 90°C, and contact angle was measured manually. The effects of dilution and/or sulphate spiking on the observed IFT and contact angle measurements were investigated using a proposed brine categories-based plotting technique. Natural SW and its sulphate-spiked versions have shown the least oil/brine IFT at ambient and 90°C conditions. The sulphate-spiked SW and its dilutions have resulted in the reduction in oil/brine IFT, whereas the diluted SW showed an increase in oil/brine IFT. Further reduction in IFT was observed at the elevated temperature. SW and SW/50 (50 times diluted sea water) were the only two brines that could yield a contact angle of 113°and 114°, respectively, indicating the change in wettability from oil-wet to the border line of intermediate-wettability conditions. The natural SW that contains 3944 mg/L of sulphate ion has been found to be the most effective in promoting wettability change and thus represents the selected smart water for EOR implementation in Asab oil field. The contact angle measurements were made from the drops formed by the natural drainage process. These measurements are believed to duplicate contact angles in the selected reservoir because of the continuous change in fluids saturation.
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