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Miscible gas injection in tight/shale oil reservoirs presents a complex problem due to various factors, including the presence of a large number of nanopores in the rock structure and asphaltene and heavy components in crude oil. This method performs best when the gas injection pressure exceeds the minimum miscibility pressure (MMP). Accordingly, accurate calculation of the MMP is of special importance. A critical issue that needs to be considered is that the phase behavior of the fluid in confined nanopores is substantially different from that of conventional reservoirs. The confinement effect may significantly affect fluid properties, flow, and transport phenomena characteristics in pore space, e.g., considerably changing the critical properties and enhancing fluid adsorption on the pore wall. In this study, we have investigated the MMP between an asphaltenic crude oil and enriched natural gas using Peng-Robinson (PR) and cubic-plus-association (CPA) equations of state (EoSs) by considering the effect of confinement, adsorption, the shift of critical properties, and the presence of asphaltene. According to the best of our knowledge, this is the first time a model has been developed considering all these factors for use in porous media. We used the vanishing interfacial tension (VIT) method and slim tube test data to calculate the MMP and examined the effects of pore radius, type/composition of injected gas, and asphaltene type on the computed MMP. The results showed that the MMP increased with an increasing radius of up to 100 nm and then remained almost constant. This is while the gas enrichment reduced the MMP. Asphaltene presence changed the trend of IFT reduction and delayed the miscibility achievement so that it was about 61% different from the model without the asphaltene precipitation effect. However, the type of asphaltene had little impact on the MMP, and the controlling factor was the amount of asphaltene in the oil. Moreover, although cubic EoSs are particularly popular for their simplicity and accuracy in predicting the behavior of hydrocarbon fluids, the CPA EoS is more accurate for asphaltenic oils, especially when the operating pressure is within the asphaltene precipitation range. [ABSTRACT FROM AUTHOR]

• The joint effects of ultrasound and solvation on oil viscosity were investigated. • The analysis of asphaltene structure by using FTIR and microscopy techniques. • The lowest viscosity was found for irradiation-then-dilution-treated crude oil. • Ultrasonic solvation reduced the ratio of aromatic rings to aliphatic chains. Production from heavy oil reservoirs faces challenges, such as accumulating heavy hydrocarbon materials like asphaltenes near the wellbore, resulting in low recovery rates. To enhance recovery and prevent formation damage, methods often focus on reducing oil viscosity. Solvents and ultrasonic waves have proven effective in this regard, though challenges related to asphaltene aggregation and structural changes persist. This study explores the impact of simultaneously applying ultrasonic radiation and solvents on crude oil's viscosity and asphaltene structure. Toluene and n-heptane, representing aromatic and paraffinic solvents, were employed. Viscosity measurements and Fourier transform infrared spectroscopy tests were conducted on sonicated crude oil diluted with solvents and solvent-diluted crude oil subjected to sonication. Results were compared to untreated and separately treated crude oil samples. The study found that the most effective viscosity reduction method involved blending sonicated oil with toluene under optimal radiation time and concentration conditions. Two primary mechanisms for viscosity reduction were identified. Firstly, there was the dissolution and aggregation of asphaltene clusters. Secondly, chemical changes in asphaltene molecular structure were observed, altering the ratio of aromatic rings to aliphatic chains. This research offers potential insights into how ultrasonication and solvation interact to modify crude oil structure. [Display omitted] [ABSTRACT FROM AUTHOR]

Production from heavy asphaltenic oil reservoirs poses several challenges that require new and innovative techniques for improved production and recovery. The main objective of this study is to experimentally investigate the influences of ultrasonic waves and solvent on oil viscosity, asphaltene precipitation behavior, and recovery of a heavy asphaltenic crude oil. This study is divided into two main parts. In the first part, crude oil samples were subjected to ultrasonic radiation with a frequency of 20 kHz and varying output powers (30, 60, and 100 W) for various durations. The viscosity of each oil sample was measured immediately after stopping ultrasonic radiation and also after 24 h of irradiation. An optimum time for ultrasound radiation was determined when the cooled-down radiated oil reached a minimum viscosity. We then measured the viscosity of the ultrasonically treated oil samples blended with a solvent (i.e., n-heptane) to assess the synergetic effect of ultrasonic radiation and solvation on the oil viscosity. In the second part, the application of ultrasonic radiation on the asphaltene aggregates and oil recovery was examined using solvent flooding in a transparent porous medium. Four sets of experiments were undertaken where the solvent was injected into the micromodel saturated with the untreated and ultrasonically treated oil free from or blended with the solvent. The results showed that ultrasonic treatment decreased the size of asphaltene aggregates and consequently reduced the viscosity of the crude oil. As a result, the suspension of asphaltene in the ultrasonically treated oil increased and reduced its tendency to precipitate at the optimum radiation time. Furthermore, the results indicated that the combined use of ultrasound and solvent had the greatest reduction in the oil viscosity compared to the untreated crude oil with ultrasonic waves or solvent. • The joint effect of ultrasonic radiation and solvent on viscosity and asphaltene aggregation of crude oil was investigated. • A synergy in viscosity reduction was found when the solvated crude oil was subjected to ultrasonic radiation. • The flooding tests showed that ultrasonic radiation locally decreased the size and precipitation of asphaltene aggregates. • The ultrasonicated oil was displaced more efficiently on the local pore space. • Considerably lower asphaltene precipitation was found when the radiated oil was displaced by the solvent. [ABSTRACT FROM AUTHOR]

• Simultaneous Effects of ultrasonic irradiation and α-Fe 2 O 3 nanoparticles (NPs) on crude oil properties were investigated. • The viscosity of irradiated oil with NPs was found to be less than that of irradiated oil without NPs. • The post-pyrolysis mass loss of the irradiated NP-added oil was greater than that of non-irradiated oil with/without NPs. • Regarding the thermogravimetric tests, the addition of NPs and the ultrasonic irradiation work in the opposite direction. In this work, the effects of ultrasonic irradiation assisted by α-Fe 2 O 3 nanoparticles (NPs) on the evolution of viscosity and thermal properties of crude oil are evaluated. A viscous crude oil with a high amount of asphaltene (∼20% by mass) was used for ultrasonication over different exposure times and nanoparticle concentrations. The viscosity of the oil before and after ultrasonic irradiation was measured with and without nanoparticles. Experimental results indicated that the viscosity of irradiated oil containing nanoparticles at optimum conditions was lower than the viscosity of nanoparticle-free irradiated oil. The thermal behavior of the irradiated crude oil mixed with nanoparticles at optimum conditions was examined using the TGA/DTA methods. The results showed a non-complementary effect of ultrasonic irradiation and nanoparticles on the weight loss and the amount of residual oil at both the end of the pyrolysis and oxidation stages, representing that addition of the α-Fe 2 O 3 NPs to the crude oil and the ultrasonication of the crude oil work in the opposite direction. Based on the TG/DTA data, the kinetic parameters of the pyrolysis and oxidation reactions were estimated. It was found that the simultaneous use of ultrasonic irradiation and nanoparticles sharply decreased the activation energy of the oxidation reactions, but had almost no effect on the activation energy of the pyrolysis reactions. The results of this paper provide an insight into the effectiveness of in-situ combustion enhanced oil recovery, which depends on viscosity reduction and the rate at which heat is generated. [ABSTRACT FROM AUTHOR]

Highlights In this study, the influence of ultrasonic waves on the viscosity and thermal behaviour of a crude oil with high asphaltene content at different irradiation times and powers/frequencies was investigated. It was found that the ultrasonic radiation significantly reduced the oil viscosity before the oil cooled down. The viscosity was then remeasured after the irradiated oil cooled down to the ambient temperature to evaluate the reversibility in viscosity at various time intervals. For each ultrasonic frequency, an optimum irradiation time was found at which the cooled-down irradiated oil reached a minimum viscosity. For the ultrasonic radiation with a frequency of 46 kHz and an output power of 50 W, it was found that the permanent viscosity loss of the cooled-down oil irradiated for an optimum time of 8 min was 10 %. The effects of ultrasonic irradiation on thermal behaviour of the oil were analysed using thermogravimetric and differential thermal (TGA/DTA) methods to evaluate the relation between changes in viscosity and thermal properties of the oil. It was found that the weight loss of the irradiated-oil was more than that of the non-irradiated oil at the end of both the pyrolysis and oxidation stages. [ABSTRACT FROM AUTHOR]