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1. An Experimental Investigation of Asphaltene Aggregation Under Carbon Dioxide Injection Flow in Ultra-Low-Permeability Pore Structure

   https://doi.org/10.2118/208950-MS  

   Elturki, Mukhtar; Imqam, Abdulmohsin (March 2022, SPE Canadian Energy Technology Conference, Calgary, Alberta)

   Abstract One of the major problems during gas injection in unconventional reservoirs is asphaltene precipitation and deposition. Asphaltenes can reduce the pore throat in the reservoir and plug the surface and subsurface equipment during the production process, thus, result in oil production reduction with significant financial consequences. The impact of carbon dioxide (CO2) gas injection on asphaltene deposition in unconventional reservoirs still poorly investigated. This research investigates the impact of CO2 gas injection on asphaltene aggregation in ultra-low-permeability pore structures, mainly present in unconventional shale resources. First, the minimum miscibility pressure (MMP) of crude oil with CO2 was determined using the slim tube technique. Then, several CO2 injection pressures were selected to conduct the filtration experiments using a specially designed filtration apparatus. All pressures selected were below the MMP. Various sizes of filter paper membranes were used to study the effect of pore structure on asphaltene deposition. The results showed that asphaltene weight percent was increased by increasing the pressure and a significant asphaltene weight percentage was observed on smaller pore size structures of the filter membranes. The visualization tests revealed the process of asphaltene precipitation and deposition and showed that asphaltene particles and clusters were precipitated after one hour and fully deposited in the bottom of the test tube after 12 hours. High-resolution photos of filter paper membranes were presented using microscopy imaging and scanning electron microscopy (SEM) analysis; these photos highlighted the asphaltene particles inside the filter paper membranes and pore plugging was observed. The study's findings will contribute to a better understanding of the main factors influencing the stability of asphaltene particles in crude oil under immiscible CO2 injection pressure, particularly in nano pores, which are predominant in shale unconventional resources. 

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2. Characterization of nanoparticles used as precipitant agents for in situ upgrading of heavy crude oils via single particle inductively coupled plasma mass spectrometry (spICP-MS)

   https://doi.org/10.1016/j.fuel.2024.133452  

   Hebert, Deja; Salas-Ortiz, Yanila; Nelson, Jenny; Ovalles, Cesar; Lopez-Linares, Francisco; Rogel, Estrella; Poirier, Laura; Zito, Phoebe (February 2025, Fuel)

   The characterization of nanoparticles (NPs) in hydrocarbon matrices using single particle inductively coupled plasma mass spectrometry (spICP-MS) is underdeveloped. There are less than ten publications using spICP-MS in hydrocarbon matrices, and none have applied the technique to determine NP concentration and size distribution in asphaltenes after in-situ upgrading of heavy oils via solvent deasphalting. To our knowledge, no studies have used spICP-MS to track the nature of NP additives in the asphaltene fraction in hydrocarbons without adulteration of the sample. Particle number concentrations (PNC) derived from spICP-MS in hydrocarbon matrices are reported for the first time. Fe2O3 PNC increased by an order of magnitude, and NiO PNC increased 28 % compared to samples without additives, indicating that NPs were reasonably well-dispersed in the asphaltenes. Ionic concentrations were higher for Ni than Fe, which showed negligible changes in all samples. Here, we report the lowest size detection limits recorded for Fe2O3 NPs (32 nm ± 1 nm) using spICP-MS in hydrocarbon matrices. Further, NiO and Fe2O3 NP sizes matched the initial sizes added to the oil before precipitation, providing evidence that the nature of the NPs does not change after deasphaltation and subsequent mixing with asphaltenes. This study expands our understanding of the interactions between metal NPs and asphaltenes when used as co-precipitants during in situ upgrading of heavy crude oil. 

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3. Kinetic Experimental and Modeling Evaluations of Asphaltene Morphology and Growth Rate under Varying Temperature and Brine Conditions

   https://doi.org/10.2118/213811-MS  

   Quainoo, Kwamena Ato; Abdulmohsin, Imqam; Borecho Bavoh, Cornelius (June 2023, SPE)

   ABSTRACT The utilization of predictive mechanisms to resolve asphaltene precipitation during oil production is a cleaner and less expensive means than the mechanical/chemical remediation techniques currently employed. Existing models lack predictive success due to opposing views on temperature-asphaltene precipitation interactions. In this study, the effect of varying temperatures (40, 50, 60, 70 80 and 90 °C) and brine concentrations (0 – 5 wt.%) on the long-time kinetics of asphaltene precipitations was evaluated. A series of experiments were conducted using the filtration technique and the confocal microscopy to study asphaltene precipitation on a model oil system consisting of asphaltenes, a precipitant, and a solvent. Furthermore, the Avrami modeling technique was employed to predict the morphology, and growth rate of the precipitating asphaltenes. The experimental results suggested that temperature significantly affects asphaltene precipitation including imparting its precipitation mechanism with a cross-behavioral pattern. Asphaltene precipitation in the system displayed an initial fast kinetics upon increasing temperature. The fast kinetics observed in the early times is due to the increasing dipole-dipole interactions between asphaltene sub-micron particles stimulated by increased temperature. However, the pattern changes into slower precipitations as the time progresses upon continuous heating of the reservoir fluid. The reason is the increased solubility of the asphaltenes imparted into the model oil system upon further increments in temperature. The presence of brine in the model-oil system also enhanced the rate and precipitation of asphaltenes. The experimental data were further analyzed with the Avrami crystallization fitting model to predict the formation, growth, morphology, and growth geometry of the precipitating asphaltenes. The Avrami model successfully predicted the asphaltene morphologies, growth rates and the crystal growth geometries. The growth geometries (rods, discs, or spheres) of the asphaltenes in the model oil systems upon temperature increments, ranged from 1.4 – 3.5. These values are indicative that temperature impacts the growth process of asphaltenes in the model system causing variations from a rod-like sporadic process (1.0 ≤ n ≤ 1.9) to a spherical sporadic growth process (3.0 ≤ n ≤ 3.9). This work precisely emphasizes the impact of temperature on asphaltene precipitations under long kinetic time, thus, providing a clear pathway for developing successful kinetic and thermodynamic models capable of predicting asphaltene precipitation reliably. The accurate prediction of asphaltene precipitation will eliminate the need for the use of harmful remediation solvents like benzene/toluene/ethylbenzene/xylene (BTEX). This study is therefore a critical step in the right direction to achieving accurate predictive model evaluations of asphaltene precipitations. 

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4. Precipitant Effects on Aggregates Structure of Asphaltene and Their Implications for Groundwater Remediation

   https://doi.org/10.3390/w12082116  

   Hammond, Christian B.; Wang, Dengjun; Wu, Lei (August 2020, Water)

   Asphaltenes generally aggregate, then precipitate and deposit on the surfaces of environmental media (soil, sediment, aquifer, and aquitard). Previous studies have recognized the importance of asphaltene aggregates on the wettability of aquifer systems, which has long been regarded as a limiting factor that determines the feasibility and remediation efficiency of sites contaminated by heavy oils. However, the mechanisms/factors associated with precipitant effects on asphaltene aggregates structure, and how the precipitant effects influence the wettability of surfaces remain largely unknown. Here, we observe the particle-by-particle growth of asphaltene aggregates formed at different precipitant concentrations. Our results show that aggregates for all precipitant concentrations are highly polydisperse with self-similar structures. A higher precipitant concentration leads to a more compacted aggregates structure, while precipitant concentration near to onset point results in a less compact structure. The well-known Smoluchowski model is inadequate to describe the structural evolutions of asphaltene aggregates, even for aggregation scenarios induced by a precipitant concentration at the onset point where the Smoluchowski model is expected to explain the aggregate size distribution. It is suggested that aggregates with relative high fractal dimensions observed at high precipitant concentrations can be used to explain the relatively low Stokes settling velocities observed for large asphaltene aggregates. In addition, asphaltene aggregates with high fractal dimensions are likely to have high density of nanoscale roughness which could enhance the hydrophobicity of interfaces when they deposit on the sand surface. Findings obtained from this study advance our current understandings on the fate and transport of heavy oil contaminants in the subsurface environment, which will have important implications for designing and implementing more effective and efficient remediation technologies for contaminated sites. 

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5. Asphaltene Precipitation and Deposition under Miscible and Immiscible Carbon Dioxide Gas Injection in Nanoshale Pore Structure

   https://doi.org/10.2118/210592-PA  

   Elturki, Mukhtar; Imqam, Abdulmohsin (June 2022, SPE Journal)

   Summary Asphaltene precipitation and deposition is considered one of the prevailing issues during carbon dioxide (CO2) gas injection in gas enhanced oil recovery techniques, which leads to pore plugging, oil recovery reduction, and damaged surface and subsurface equipment. This research provides a comprehensive investigation of the effect of immiscible and miscible CO2 gas injection in nanopore shale structures on asphaltene instability in crude oil. A slimtube was used to determine the minimum miscibility pressure (MMP) of the CO2. This step is important to ensure that the immiscible and miscible conditions will be achieved during the filtration experiments. For the filtration experiments, nanocomposite filter paper membranes were used to mimic the unconventional shale pore structure, and a specially designed filtration apparatus was used to accommodate the filter paper membranes. The uniform distribution (i.e., same pore size filters) was used to illustrate the influence of the ideal shale reservoir structure and to provide an idea on how asphaltene will deposit when utilizing the heterogeneous distribution (i.e., various pore size filters) that depicts the real shale structure. The factors investigated include immiscible and miscible CO2 injection pressures, temperature, CO2 soaking time, and pore size structure heterogeneity. Visualization tests were undertaken after the filtration experiments to provide a clear picture of the asphaltene precipitation and deposition process over time. The results showed an increase in asphaltene weight precent in all experiments of the filtration tests. The severity of asphaltene aggregations was observed at a higher rate under miscible CO2 injection. It was observed that the miscible conditions have a higher impact on asphaltene instability compared to immiscible conditions. The results revealed that the asphaltene deposition was almost equal across all the paper membranes for each pressure used when using a uniform distribution. Higher asphaltene weight percent were determined on smaller pore structures of the membranes when using heterogeneous distribution. Soaking time results revealed that increasing the soaking time resulted in an increase in asphaltene weight precent, especially for 60 and 120 minutes. Visualization tests showed that after 1 hour, the asphaltene clusters started to precipitate and could be seen in the uppermost section of the test tubes and were fully deposited after 12 hours with less clusters found in the supernatant. Also, smaller pore size of filter membranes showed higher asphaltene weight percent after the visualization test. Chromatography analysis provided further evaluation on how asphaltene was reduced though the filtration experiments. Microscopy and scanning electron microscopy (SEM) imaging of the filter paper membranes showed the severity of pore plugging in the structure of the membranes. This research highlights the impact of CO2 injection on asphaltene instability in crude oil in nanopore structures under immiscible and miscible conditions. The findings in this research can be used for further research of asphaltene deposition under gas injection and to scale up the results for better understanding of the main factors that may influence asphaltene aggregation in real shale unconventional reservoirs. 

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