Asphaltene precipitation modeling in dead crude oils using scaling equations and non-scaling models: comparative study

This research study aims to conduct a comparative performance analysis of different scaling equations and non-scaling models used for modeling asphaltene precipitation. The experimental data used to carry out this study are taken from the published literature. Five scaling equations which include Rassamadana et al., Rassamdana and Sahimi, Hu and Gou, Ashoori et al., and log–log scaling equations were used and applied in two ways, i.e., on full dataset and partial datasets. Partial datasets are developed by splitting the full dataset in terms of Dilution ratio (R) between oil and precipitant. It was found that all scaling equations predict asphaltene weight percentage with reasonable accuracy (except Ashoori et al. scaling equation for full dataset) and their performance is further enhanced when applied on partial datasets. For the prediction of Critical dilution ratio (Rc) for different precipitants to detect asphaltene precipitation onset point, all scaling equations (except Ashoori et scaling equation when applied on partial datasets) are either unable to predict or produce results with significant error. Finally, results of scaling equations are compared with non-scaling model predictions which include PC-Saft, Flory–Huggins, and solid models. It was found that all scaling equations (except Ashoori et al. scaling equation for full dataset) either yield almost the same or improved results for asphaltene weight percentage when compared to best case (PC-Saft). However, for the prediction of Rc, Ashoori et al. scaling equation predicts more accurate results as compared to other non-scaling models.

Effect of viscosity on oil recovery by spontaneous imbibition from partially water-covered matrix blocks

Spontaneous imbibition is an important mechanism of oil recovery from fractured reservoirs and unconventional reservoirs. Oil is produced by combining co- and counter-current imbibition when the matrix blocks was partially covered by water. In this paper, we focused on the effect of viscosity ratios on oil production by spontaneous imbibition and established the numerical model for one-dimensional linear imbibition with TEO-OW boundary conditions, which was validated by the experimental data. The effect of viscosity ratio on co- and counter-current imbibition is investigated and scaling result of the imbibition recovery curve for wide range of viscosity ratio using the conventional scaling equation was tested, which indicates that the close correlation was achieved only when oil-water viscosity ratios are higher. Then, a modified scaling equation was developed based on the piston-like assumption for one-dimensional co-current imbibition and close correlation of imbibition recovery curves was achieved when viscosity ratios are lower. Finally, correlation of imbibition recovery curves was improved for wide range of viscosity ratios by combining conventional and modified scaling equation. Results show that since the shape of imbibition recovery curves is not similar for different viscosity ratios, it is difficult to obtain the perfect correlation using the constant viscosity term.