Asphaltenes have reputation for being the heaviest and most problematic fraction of crude oil, which can be appreciably existed in heavy oils. The asphaltene molecules are the most polarizable fractions since they comprise highest percentage of the heteroatoms (O, N, S) compared to the other crude oil constituents. Asphaltenes are large complex molecules containing polyaromatic core with circumferential aliphatic chains, which the heteroatoms could emerge in both polyaromatic core and aliphatic chains [[1], [2], [3]]. In practical, the asphaltenes show a board spectrum of various molecular structures and defined based on the solubility, which in normal alkanes such as pentane and heptane are insoluble, and in aromatic hydrocarbons such as toluene and benzene are soluble [[4], [5], [6]].

Molecular structure of asphaltene fractions is classified into two main architectures: in continental (Island) models the peripheral aliphatic chains are attached to the single polyaromatic core and in archipelago models the several small aromatic cores are joined by aliphatic chains [[7], [8], [9], [10]]. The effect of molecule size, aromatic character, and polarity on the size, shape, and cluster topologies of asphaltene nanoaggregates was demonstrated by the use of a realistic polydisperse molecular model [11]. By evaluating aggregation behavior, a comparison was made between a unistructural and a multistructural approach to representing asphaltene fractions. The findings revealed that the multistructural approach provides a more accurate reproduction of data obtained from elemental analysis compared to the unistructural approach [12,13].

Oil production confront multiple challenges which one of them is the deposition and precipitation of heavy components of the crude oil such as asphaltenes and wax. This may result in obstruction of pore throats, well-bores and pipelines, and reduction of permeability [14]. Deposition of Asphaltenes increments maintenance costs and decreases the oil recovery. The pressure drop owning to exploitation from oil reservoir, change in temperature or mole fraction of constituents of crude oil can lead to the destabilization of asphaltene molecules [15,16].

In petroleum industry, the operating methods in order to control the asphaltene deposition are mainly categorized into the removal of asphaltene deposition and prevention techniques. The mechanical approaches, chemical and thermal treatments are extensively utilized to eliminate the asphaltene depositions [17,18]. However, the treatment methods temporarily clean the production facility and asphaltene molecules persistently deposit. Hence, the prevention methods have gained tremendous attentions to prevent the formation of asphaltene nanoaggregates in the early stages [19,20]. The inhibitors are designed to mitigate the precipitation of asphaltenes in a wide range of thermodynamic conditions [[21], [22], [23]]. Variant materials such as ionic liquids [24], polymers [25], nanoparticles [26] and surfactants [27], with identical mechanism, connecting to the asphaltene molecules by means of polar section and constructing the steric repulsion via non polar section disperse asphaltene molecules in crude oil.

Nano particles due to their high surface to volume ratio and functional surface area, depict the high performance to adsorb asphaltene molecules. The small size of nanoparticles authorizes them to penetrate pores and easily distribute in the reservoir. Therefore, nanotechnology has attracted remarkable interest as inhibitor to reduce asphaltene aggregation [[28], [29], [30], [31], [32], [33]]. It has been reported that nanoparticles render a larger surface area exhibited more efficiency to adsorb asphaltene molecules. For example, the NiO NPs owning to their higher surface area than Co3O4 and Fe3O4 NPs showed highest tendency to asphaltene adsorption [34]. Similarly, greater affinity of SiO2 NPs to adsorb asphaltene is ascribed to their larger surface area in comparison with that of the Al2O3 and MgO NPs and results illustrated that MgO NPs act more efficient than Al2O3 NPs [35]. Another study demonstrated that the adsorbtion magnitude of n-C7 asphaltene with the nano scale slica NPs is higher than the micro scale slica NPs attributed to their considerable dispersibility and available surface area exposed to adsorption [36]. The coated NPs interact strongly with Asphaltene molecules presumably traced back to the high extent of interaction sites and improved strength of the interaction [37]. Polythiophene (PT) coated magnetic Fe3O4 NPs are adopted by Setoodeh et al. in order to examine the adsorption of asphaltene molecules in both synthetic asphaltene-toluene solution and crude oil. It is revealed that the PT coated NPs efficiently adsorb more asphaltenes compared to the uncoated NPs. Furthermore, the obtained results in asphaltene-toluene solution depict the maximum adsorption capacity (Qmax) values of 0.79 and 1.09 mg. m−2 for uncoated and PT coated Fe3O4 NPs, respectively [36]. In another study Setoodeh et al. investigated the potential of the synthesized Fe3O4 NPs coated with PT, Mil-101 (Cr) (MOF), graphene oxide (GO), SiO2, and chitosan for inhabitation of asphaltene precipitation in crude oil. The experiments were implemented with a constant concentration of 10 g/l for all NPs. PT-coated Fe3O4 NPs displayed the most superb performance and the adsorption capacity of NPs coated with PT, Mil-101 (Cr) (MOF), graphene oxide (GO), chitosan, and SiO2 decreased, respectively [38].

Molecular dynamics (MD) solves Newton's equation of motion to execute the virtual experiments; meanwhile, high-performance computers play a vital role. Many a MD simulations conducted before the experiments are implemented in the real world. Moreover, MD simulations are performed due to their capability of providing detailed properties and information of systems at the atom level. In the last decades, MD simulations have gained considerable interest in the field of enhanced oil recovery (EOR) [[39], [40], [41], [42]].

The behavior of asphaltene molecules in the presence of the Dodecyl benzene sulfonic acid (DBSA) as inhibitor were examined in the heptol (n-heptane/toluene) solutions. The DBSA displayed high efficiency in diminishing the amount and rate of aggregation. Consequently, incrementing the solvation of asphaltene molecules. Besides, the performance of the DBSA improved as much as the concentration of it increased [43].

Tazikeh et al. investigated the impression of TP-coated Fe3O4 NPs and Fe3O4 NPs on the aggregation process of asphaltene molecules by employing the MD simulations. The size and the number of asphaltene molecules of aggregates divulge the inhabitation effect of both TP-coated and uncoated NPs in comparison with the NPs-free-case. In addition, the number of adsorbed asphaltene molecules onto the TP-coated NP are higher than uncoated NP [44]. The influence of hydrophobicity of silica surface altered by adjusting the hydrophilic and hydrophobic ratios on adsorption of asphaltene molecules was examined. In both fully hydrophilic and hydrophobic silica surfaces exhibited a great tendency was seen to adsorb asphaltene molecules in form of tilted. However, the partially hydrophilic or hydrophobic silica surfaces tend to adsorb more asphaltene molecules in form of tiled [45]. Xiong et al. studied the aggregation of the C5PeC11 and C5Pe asphaltene molecules and adsorption of them onto the silica surface in the heptol solvents. The observations disclosed that the C5Pe molecules owing to the shorter aliphatic chains formed larger aggregation and represent lower solubility than C5PeC11 molecules. A greater number of C5PeC11 molecules tend to be adsorbed onto the silica surface than the C5Pe molecules [46].

Regardless of the numerous studies on asphaltene inhibitors, to date, Carbon Nano Tube (CNT) particles as asphaltene inhibitors have not been comprehensively investigated by MD simulation tool. In this work, our interest lies in rendering the microscopic insight into asphaltene molecules aggregation and the inhabitation effect of CNTs through the MD simulations medium. The aggregation size and how the bare and functionalized CNTs can increase the dispersibility and solvation of asphaltene molecules will be investigated by analyzing the interaction energy, hydrogen bond, solvent accessible surface area (SASA), radial distribution function (RDF), etc. Due to the large surface area of the CNTs, the impression of the CNTs’ surface area and carboxyl dosages will be simultaneously studied in detail. PMF calculations will be carried out to investigate the effect of carboxyl groups on the CNTs' properties.