Modification of e-CPA for estimating phase equilibria and development of predictive models for electrical conductivity in aqueous electrolyte solutions

We modify the electrolyte cubic plus association equation of state (e-CPA EoS) and inetgrate it with two electrical conductivity models to estimate the electrical conductivity of 11 monovalent electrolytes solutions in water. The e-CPA EoS is modified by including the ion-ion and ion-solvent association interactions and tuned using experimental data of mean ionic activity coefficient and density of the electrolyte solutions. The modified e-CPA model shows a better performance in estimating the bubble pressure data. The hybridization of two electrical conductivity models with e-CPA results in two predictive models for estimating the electrical conduction of dilute and concentrated electrolyte solutions. Finally, we generalize these predictive models by correlating their model fitting parameters to the electrolyte physical parameters such as mean hard-sphere diameter or to association volume. The two predictive electrical conductivity models estimate electrical conductivity with AARD of 11.15 % and 13.87 % over wide ranges of temperature and electrolyte concentration.Publishers versio

Characterization of crude oils and asphaltenes using the PC-SAFT EoS: A systematic review

In this paper, we present a systematic review of the perturbed-chain statistical associating fluid theory equation of state (PC-SAFT) EoS for thermodynamic modeling with application in asphaltene phase behavior simulation. The SAFT EoS and its modified version known as the PC-SAFT EoS is briefly introduced. Then, uses of the PC- SAFT EoS as a tool for asphaltene phase behavior modeling is highlighted. Crude oil characterization methods and modeling procedures are described with a focus on SARA-based method of modeling. The effects of varia-tions in temperature and pressure on the PC-SAFT asphaltene precipitation models are discussed, as well. An erroneous behavior of PC-SAFT models at low temperatures was noted in the literature for a number of crudes. To address this issue, a summary of approaches developed to deal with such problems is presented. The effect of other modeling aspects on accuracy such as binary interaction parameters, inclusion of association term, and asphaltene polydispersity are discussed. The interaction parameters have a profound effect on modeling of precipitation envelope. Inclusion of association term seems to be especially promising in developing more ac-curate asphaltene phase behavior models. Modeling asphaltene fraction as polydisperse entities greatly improves the quality of models that aimed at calculation of the amount of precipitated asphaltenes. Finally, a summary of comparative studies between the PC-SAFT and some other thermodynamic models is provided.Post-print / Final draf

Estimating contact angle of pure and mixed liquids on smooth solid surfaces using dispersive-to-attractive surface energy ratio from PCP-SAFT model

This study introduces a novel methodology using the PCP-SAFT model and Young equation to estimate contact angles of pure and mixed liquids on solid surfaces. By considering the dispersion and non-dispersion contributions to the Helmholtz energy, our approach estimates the ratio of dispersion to total surface energy, that is crucial to predict contact angles. Comparing our results with literature data demonstrates high accuracy; the average absolute relative deviation (AARD) of 6.65% is achieved for estimating the ratio of dispersion surface tension to total surface tension of 13 liquids and 9.27% for estimating contact angle for 70 systems at room condition. Moreover, our model effectively captures the temperature and composition variations for binary mixtures on various surfaces, showing its applicability in understanding the wetting behavior. The PCP-SAFT model offers a promising tool for estimating the ratio of dispersion surface tension to total surface tension, required to estimate contact angle as an important measure of surface wetting.Publishers versio

Experimental investigations in improving the VAPEX performance for recovery of heavy oil and bitumen

The process of vapor extraction (VAPEX) is a recovery process which targets the heavy oil and bitumen resources. Owing to high viscosity values for these unconventional types of oil, the recovery processes in such reserves are still challenging. The unconventional oil recovery processes usually include a mechanism for reducing the oil viscosity by means of heat, solvent, or both. The process of VAPEX utilizes the injection of a light hydrocarbon solvent into a reservoir for recovering the viscous oil in place by diffusing into the oil and by providing sufficient mobility to the oil upon dilution. Although this process offers a variety of advantages over the alternative thermal recovery processes such as SAGD or CSS, it suffers from two major drawbacks. First, the oil production rates obtained in the VAPEX process are considerably lower than those obtained in the thermal processes. Second, the solvent cost is considerably high. We tried to tackle these two problems during this research and we searched for potentials for an improved VAPEX process. Three potentially improved occurrences of a VAPEX project were found when: 1) the injected solvent was superheated, 2) the wettability of media was altered to oil-wet, and 3) the vugs were distributed in the porous media. Warm VAPEX process is introduced in which the VAPEX process is thermally augmented through superheating the solvent vapor. An attractive feature of this process is the capability of the solvent in being able to condense at the bitumen-solvent interface, which provides the opportunity for the bitumen to be upgraded in-situ through asphaltene precipitation. The asphaltene precipitation was not observed during the conventional vapor extraction process and was only observed during the warm VAPEX process. Upon a moderate level of superheating, the production rate of bitumen was sufficiently improved while the solvent content of the produced oil was significantly decreased as a result of decreased solubility of solvent in the oil at elevated temperatures. Therefore, more oil was produced at lower costs. The warm VAPEX experiments were conducted at 4 temperature levels in high and low permeability media using Cold Lake bitumen and Lloydminster heavy oil blend, n-pentane was used as solvent. The warm VAPEX process was found to be more effective for Cold Lake bitumen and for less permeable media. The potential of in-situ upgrading decreased when the level of superheating increased. The second potential for an improved VAPEX process obtained when the wettability of porous medium was altered to oil-wet conditions. Although this wettability condition is harmful to steam-based recovery processes, such as SAGD, it becomes beneficial to VAPEX. For the application of VAPEX process in fractionally wet media the wettability of glass beads was altered to oil-wet conditions through silylation process, and the VAPEX experiments were conducted in a random packing of water-wet and oil-wet beads of similar size at 7 different compositions. A substantial increase in the oil production rate was observed in a completely oil-wet medium, compared to the water-wet medium. By increasing the fraction of oil-wet beads in the packing up to a critical composition, the production rate of live oil increased linearly with the increase in the fraction of oil-wet beads in the packing during the vapor extraction process. Beyond this critical composition, however, the production rate of live oil did not change significantly with further increase in the fraction of the oil-wet beads in the randomly packed medium. Vugs were also found to be beneficial to the production performance of the VAPEX process. The presence of vugs was investigated in synthesized vugular media at 4 different levels of vuggy-to-total pore volume ratios. The performance of vugular media was compared to that of the homogeneous sintered media. The vugs facilitated the production of oil during the VAPEX process by providing flow communication between the vugs and the surrounding matrix, and therefore, by providing a local high permeability pathways towards the production well. A peak in the oil production rate was observed whenever a series of vugs were simultaneously invaded by the solvent vapor. The overall production rate of oil was higher in vuggy media compared to a homogeneous media at the same overall porosity and permeability. Furthermore, the magnitude of residual oil saturation left behind was also slightly lower in vuggy medium because the vugs were perfectly drained. Finally, a constant rate air injection (CRAI) porosimetry method was developed for characterization of vugs in a vugular media. This method was successfully tested in different synthetic vugular media, and the results illustrated higher accuracy in CRAI porosimetry method compared to constant rate mercury porosimetry. CRAI porosimetry method was also employed for identification of higher permeability regions embedded in a matrix of lower permeability. The analysis of a typical porosimetry signal was also modified