Heavy Oil Water Research Articles

Research on mechanism of controlling water and stabilizing production in heavy oil reservoirs with edge-bottom water

The development of edge-bottom water heavy oil reservoirs typically involves short water-free production period and a rapid increase in water cut, leading to generally low oil recovery factors. Combining the advantages of foam and viscosity reducers for composite development can effectively address the challenges in edge-bottom water reservoirs; however, the mechanism of action remains unclear. In this study, the concentrations of foaming agent and viscosity reducer were initially determined using a foam evaluator and an Anton Paar rheometer. Subsequently, a 2D large flat plate model was employed to conduct a composite group production experiment after water flooding, and then the change in oil saturation during flooding was analyzed by measuring electrical resistance. Finally, the dynamic curves of flooding were compared to analyze the mechanism of water control and oil stabilization (WCOS). The results indicate that the 2D large flat plate model and the method of inverting saturation field maps can effectively simulate the oil-water flow behavior during the composite flooding process after water flooding. The synergistic mechanism of N2 foam controlling bottom water coning and CO2 enhanced viscosity reducer to reduce viscosity in deep areas was revealed, increasing the overall recovery factor by 10.3% compared to water flooding. The mechanism of the combined oil recovery is clarified, which providing a reference for formulating WCOS plans following water flooding.

Study on the Effect of Nitrogen Bubble Foam Flooding in Deep Heavy Oil Reservoirs with Edge And Bottom Water

Abstract The oil recovery rate is low, the degree of recovery is low and the water content rises fast after water flooding in deep edge and bottom water heavy oil reservoir in Lukeqin oilfield. In order to explore the method to improve the production effect, the integrated foam system of high temperature and high pressure resistant viscosity reduction and oil displacement is optimized. On the basis of clarifying the mechanism of improving the production effect of nitrogen foam flooding for deep heavy oil, taking the west area of Lukeqin oilfield as the research object, the parameter optimization design of nitrogen foam flooding for deep edge and bottom water heavy oil is carried out, such as injection section plug, gas-liquid ratio and injection-recovery ratio. The optimization results are as follows: the injected nitrogen foam slug is 0.2pv, the gas-liquid ratio is 1-1.2, and the injection production ratio is 1:1. The pilot test of 4 well groups was carried out on the site. After foam flooding, the injection pressure was increased by 5.2mpa, the daily oil production of the oil well was increased by 43T / D, the water cut was decreased by 45%, the accumulated oil production was increased by 32000 tons, and the oil recovery was expected to be increased by more than 10%. The purpose of improving the development efficiency of this type of oil reservoir was achieved. Using this optimization technology for scheme design and field implementation, the oil enhancement effect is remarkable and improves the benefit of deep thick oil development, which can provide technical support for the development of similar domestic reservoirs.

Research for the Enhanced Oil Recovery Mechanism of Heavy Oil after Composite Huff and Puff Assisted by Edge-Bottom Water Displacement

Abstract In the late stage of exploiting heavy oil reservoirs with edge-bottom water, we are faced with problems such as high crude oil viscosity, channeling of bottom water, and rapid rise in water cut. To clarify the synergistic effect of N2, CO2, N2 foam, and viscosity reducer in water control and oil increase, and solve the problem of edge-bottom water rushing into production wells, one-dimensional sand-pack huff and puff experiments were carried out. First, the N2 foam huff and puff experiment evaluated the effect of N2 foam on controlling bottom water. Then the viscosity reducer assisted CO2 huff and puff experiment analyzed the synergistic viscosity reduction ability between the two to mobilize the remaining heavy oil. Next, the N2 foam-viscosity reducer-CO2 huff and puff experiment clarified the synergistic effect between the three. Finally, the N2 foam-viscosity reducer-CO2-N2 huff and puff experiment solved the problem of insufficient reservoir energy based on synergistic precipitation and oil increase. Experimental results show that N2 foam-viscosity reducer-CO2-N2 huff and puff is the optimal water control and oil increase solution. This solution can significantly reduce water production and increase oil production. In the one-dimensional sand-pack experiment, this technical solution reduced the water content by 68% and increased the recovery rate by 16.09%. The research results provide a reference for the development of exploitation technology schemes for similar edge-bottom water heavy oil reservoirs after entering high water cut.

Eco-friendly bionic superwetting Janus membranes prepared from paper-based laser-induced graphene for photothermal anti-icing and on-demand oil–water separation

Laser-induced graphene (LIG) from carbon precursors is used in the manufacture of semiconductors, energy and biomedical devices. To expand its field of applications, there is a strong need to explore LIG conversion of eco-friendly precursors. An approach combining bionic structures and surface modification on paper-based LIG was investigated for producing asymmetric superwetting Janus membranes. Molecular dynamic simulation illustrates the paper-based LIG conversion mechanism. The Octadecanethiol-modified bionic crescent-shaped LIG surface exhibited superhydrophobic performance, the water contact angle (WCA) is 157° and the water sliding angle (WSA) is 3.5°. The plasma-modified LIG surface was superhydrophilic with the WCA of 0°. The Janus membranes were demonstrated for high-efficient separation of light oil–water and heavy oil–water mixtures. Furthermore, the superhydrophobic surface of the Janus membranes with excellent photothermal properties exhibited superior anti-icing capability. The proposed approach for fabrication of bionic Janus membranes would provide an eco-friendly solution to LIG applications.

The Production Analysis and Exploitation Scheme Design of a Special Offshore Heavy Oil Reservoir—First Offshore Artificial Island with Thermal Recovery

More and more offshore heavy oil resources are discovered and exploited as the focus of the oil and gas industry shifts from land to sea. However, unlike onshore heavy oil reservoirs, offshore heavy oil reservoirs not only have active edge and bottom water but also have different exploitation methods. In this paper, a typical special heavy oil reservoir in China was analyzed in detail, based on geology–reservoir–engineering integration technology. Firstly, it is identified as a self-sealing bottom water heavy oil reservoir by analyzing its geological characteristics and hydrocarbon accumulation mechanism. Secondly, the water cut is initially controlled by oil viscosity, but subsequently, by reservoir thickness through the analysis of oil and water production data. Thirdly, the bottom oil–water contact of the reservoir was re-corrected to build an accurate 3D geological model, based on the production history matching of a single well and the whole reservoir. Lastly, a scheme of thermal production coupled with cold production was proposed to exploit this special reservoir, and the parameters of steam, N2, and CO2 injection and production were optimized to predict oil production. This work can provide a valuable development model for the efficient exploitation of similar offshore special heavy oil reservoirs.

Synergistic collaborations between surfactant and polymer for in-situ emulsification and mobility control to enhance heavy oil recovery

Surfactant-polymer (SP) combined systems is an effective nonthermal method to enhance the heavy oil recovery, through in-situ emulsification and mobility control mechanisms. In this study, a novel SP system was developed using 0.2 wt% anionic surfactant (alkyl naphthol polyoxyethylene ether sulfonate, ANES) and 0.1 wt% polymer (partially hydrolyzed polyacrylamide, HPAM). The SP system had viscosity reduction rate of ∼ 98 %, viscosity ratio of oil to displaced water (μo/μd) of ∼ 3.95 and IFT of ∼ 0.29 mN/m, beneficial for decreasing the mobility ratio of water to heavy oil. Then, the applied performances including emulsion morphologies and stability, wettability alteration ability were systematically characterized. The results showed that the freshly O/W emulsions formed by SP system displayed uniform droplet size distribution, as well as high stability with tight interfacial film. In addition, the SP system exhibited excellent wettability alteration property with low contact angle of 18.3°. The synergistic collaboration mechanisms of surfactant and polymer include heavy oil–water interfacial tension reduction, in-situ emulsification, oil-viscosity reduction and water-viscosity increase. Finally, the static oil washing and dynamic sand-pack flooding experiments showed that the SP system exhibited high oil washing efficiency (62.89 %) and enhanced oil recovery efficiency (56.9 %) with improving the mobility controllability after the primary water-flooding process. This study indicated that the synergistic collaborations between surfactant and polymer had great potential to enhance the heavy oil recovery.

Doping heteroatoms to form multiple hydrogen bond sites for enhanced interfacial reconstruction and separations

Interfacial challenges in unconventional oil extraction include heavy oil–water–solid multiphase separation and corrosion inhibition. Herein, a novel strategy based on interfacial hydrogen bonding reconstruction is proposed for constructing multifunctional interfacially active materials (MIAMs) to address multi-interfacial separation needs. A simple one-pot method is applied to successfully synthesize four different MIAM varieties, integrating site groups (–NH2, OSO, –COOH, and Si–O–Si) with multiple hydrogen bonds (HBs) into allyl polyether chains. The results indicate that all synthesized MIAMs excel in demulsification, detergency, and corrosion inhibition simultaneously, even at 25 °C. Their dehydration efficiency for different water-in-oil emulsions (even heavy oil emulsion) surpasses 99.9 % even at 16 °C, showing their excellent energy-saving potential for field applications. Furthermore, they demonstrate effective, nondestructive static cleaning (up to 86 %) of adhered oil from solid surfaces at 25 °C and provide corrosion inhibition effects (up to 92.09 %) on mild steel immersed in saturated brine. Mechanistic tests reveal that incorporating multiple HB sites in MIAMs dramatically enhances their effectiveness in interfacial separations. Based on these findings, an HB-dominated noncovalent interaction reconstruction strategy is tentatively proposed to develop advanced materials for low-carbon, efficient interfacial separations.

Electrospinning janus membranes for on‐demand oil/water collection and emulsion separation

AbstractOily water pollution has become one of the most serious water environment issue in worldwide. Membrane that can effectively and efficiently remove different oil pollutions from the complex water environment is still urgently needed. Herein, a Janus membrane with opposite wettability that can separate heavy oil–water and light oil–water mixtures on demand was prepared by using a simple sequential electrospinning and chemical crosslinking method. The membrane could remove oil or water under gravity with a high oil/water flux and excellent separation efficiency. Moreover, the membrane could separate different kinds of oil‐in‐water emulsions under gravity with a high flux of 1184 L m−2 h−1 and a tiny flux loss of 4.4% after a 10‐cycle separation. Owing to its excellent anti‐pollution properties the flux recovery rate of the membrane was still higher than 80% after 150 min of emulsion separation. Additionally, the membrane also displayed the ability to transport liquid unidirectionally, giving whom the capabilities to collect oil underwater or water underoil. This research provides a novel and simple method for producing membranes for a variety of separation applications.

Asymmetrically superwetting Janus membrane constructed by laser-induced graphene (LIG) for on-demand oil–water separation and electrothermal anti-/de-icing

Superwetting functional surfaces based on laser-induced graphene (LIG) have a wide range of applications in many fields. However, single wettability LIG films are difficult to respond to complex and changing environmental conditions. Despite the large number of experiments were carried out to demonstrate the formation of LIG, there is a lack of studies on the process and formation mechanisms of LIG. In this study, the conversion of PEI to graphene was systematically investigated by both experimental and molecular dynamics simulations. A new method for obtaining Janus membranes with both superhydrophobicity and superhydrophilicity by ethanol and plasma treatment of LIG is proposed. The asymmetrically superwetting Janus membrane are shown to realize the on-demand controllable separation of light oil–water and heavy oil–water. In addition, the superhydrophobic LIG is used as a coating material with excellent electrothermal properties, which provide the performance of anti-icing and electrothermal de-icing. The asymmetrically superwetting Janus membranes prepared by the proposed simple and environmentally friendly method are shown to have a variety of prospective applications.

Continuous high viscosity biphasic liquid separation

Enhancing the efficiency of separation in high-viscosity biphasic liquid purification processes can significantly reduce energy consumption and costs. This study has developed a co-axial biphasic liquid separator that can continuously and instantaneously separate two-phase mixtures with viscosities up to 2000 mPa∙s at room temperature, to meet real industrial needs. This co-axial biphasic liquid separator uses a special helix wire structure that separates the two-phase fluids based on the difference in surface tension, unaffected by the viscosity of the liquids. In experiments with PMMA-toluene-water mixtures, the flow rate can reach up to 4000 μl/min, with PMMA recovery rates consistently above 83.6 %, and as high as 91.5 %. In experiments with undiluted heavy oil–water, a purity of up to 87.58 % was achieved for heavy oil, and for diluted heavy oil, the purity even reached as high as 92.15 %. The separator demonstrated remarkable universality and durability, maintaining stable and high-purity biphasic separation across varying flow rates, through 15 cycles of repeated use, and during prolonged operations of up to one hour, without any system failures. The co-axial biphasic liquid separator developed in this study is currently the only few microseparator in continuous processes capable of separating liquids with viscosities over 2100 mPa∙s, and it could decrease the cost of relevant process development in industrial setups, realizing the vision of green manufacturing.

Measurement of high water-cut heavy oil flow based on differential pressure of swirling flow

Real-time measurement of heavy oil production is critical to ensure stable production. Due to the complex kinematic characteristics of heavy oil, existing methods cannot accurately measure its flow rate and water cut. In this paper, a novel method is proposed to measure the high water-cut heavy oil flow by using the differential pressure of the two-phase swirling flow in the pipe. For the swirling flow in the pipe, the radial differential pressure and the axial differential pressure exist simultaneously, which are very sensitive to the flow rate and water cut. The formation mechanism of the two kinds of differential pressure is analyzed theoretically, and their relationship with flow rate and water cut is studied by experiment and numerical simulation. The measurement model of heavy oil–water two-phase flow on the above relations is validated by field experiments. The radial differential pressure is only related to the two-phase flow rate, varying exponentially with the flow rate when the oil viscosity is greater than 10 000 mPa s. This characteristic is very useful for the heavy oil–water two-phase flow measurement. The axial differential pressure decreases with the increase in water cut in cases of water cut <85%, while it increases with the water cut in cases of water cut >85%. With the increase in water cut, the ratio of axial differential pressure to radial differential pressure first decreases and then increases. The relative errors of the established measurement model for flow rate and water cut are 0.19%–17.92% and 0.21%–15.5%, respectively, and more than 70% of the measurements with a relative error of less than 10%. The study of the heavy oil–water two-phase flow measurement method can optimize the measurement cost and accelerate the process of intelligent oilfield construction.

Two‐Phase Relative Permeability Curves of Bingham Heavy Oil Under Different Types of Wettability: A Theoretical Model

As an important and universal petrophysics of heavy oil reservoirs, the two‐phase flow ability inside porous medium is vital for heavy oil development. Utilizing the laminar flow theory and an ideal pore structure, especially cylinder model, the function of the relative permeability of heavy oil–water with water saturation is derived by incorporating the principles of momentum conservation and the characteristics of Bingham fluids, which was modified by validated experiment. Two‐phase relative permeability, considering heavy oil as non‐Newtonian fluid, is the function of water saturation, pore size, oil–water viscosity ratio, and yield stress. The results of the validated experiment show that the theoretical values calculated employing the modified equation exhibit better agreement with the experimental values, particularly when the viscosities of two‐phase fluid are great. The results of the modified two‐phase relative permeability show a decrease in water saturation interval corresponding to the two‐phase flow area and a smaller value of permeability at equal two‐phase relative permeability. The oil–water viscosity ratio in the hydrophobic pores affects the water‐phase relative permeability, although the magnitude of its influence diminishes as the viscosity ratio increases. The behavior of relative permeability in hydrophilic pores is the opposite of that in hydrophobic pores. This work can afford good application prospects for mobility control in multilayered reservoirs through the heterogeneous‐phase‐composite fluid. The saturations of the remaining oil and irreducible water also play a vital role in the prediction of permeability. The work can afford good application prospects for the flow behavior of Bingham heavy oil in pores with different types of wettability.

Simulation study on the coupled heat and mass transfer of CO2 in a heavy oil-water liquid system based on an improved lattice Boltzmann (LB) method

This study investigates the heat and mass transfer when low-temperature CO2 diffuses in a heavy oil–water liquid system based on an improved Lattice Boltzmann (LB) method. First, we determine the CO2 diffusion coefficients in heavy oil and water and the heat transfer coefficients of heavy oil and water using the pressure drop (DP) method and the laser flash (LF) method, respectively. Then, a numerical model that couples the heat and mass transfer in the system is established based on the improved LB method. The effect of low-temperature CO2 on the temperature field of the system and the effect of changes in the temperature field on CO2 diffusion are investigated. Finally, we develop a micro-model reproducing the heat and mass transfer of CO2 in water and heavy oil-saturated porous media to validate the accuracy of the numerical model. The results demonstrate that the CO2 diffusion coefficients in heavy oil and water linearly increase with the temperature increases. The heat transfer coefficients of heavy oil and water are insensitive to the changes in temperature. The heat transfer process has a great impact on the mass transfer of CO2 in the liquid system. The CO2 diffusion velocity slows down as the system temperature decreases because of the heat transfer (from 400 K to 300 K), leading to a reduction percentage of 300 % in the CO2 front movement velocity. Compared to the scenarios neglecting heat transfer, CO2 diffusion distance and amount decrease by 38 % and 50 %, respectively because of the changes in the temperature field of the system.

Robust and self-healing under-liquid superlyophobic coating fabricated by a universal strategy for polar-nonpolar liquid separation

Surfaces showing desirable under-liquid superlyophobicity have attracted great interests due to their high potential applications, especially in the liquid separation. Nevertheless, it still remains a challenge to put forward a universal strategy to fabricate robust under-liquid superlyophobic surfaces with self-healing function. Herein, a highly durable and self-healing under-liquid superlyophobic coating is developed that can be applied onto various substrates (e.g., cotton, polyester, filter paper, wool, hemp, sponge, lyocell, etc.) via a two-step coating process, through depositing silica nanoparticles partially grafted by octadecylamine followed by crosslinking of polyurethane macromolecules containing polysorbate20. The obtained substrates show superamphiphilic in air, under-water superoleophobic and under-oil superhydrophobic properties. High-efficiency separations of polar-nonpolar liquids, e.g., water-heavy oil, water-light oil, immiscible organic liquid mixtures, can be achieved when the coated fabric was used as the separation membrane. Moreover, such under-liquid superlyophobic coating demonstrates excellent durability against repeated washing, long time UV irradiation, organic solvent attack, high temperature and plasma treatment. Even the coating surface is damaged chemically or physically, its original superwetting property can be recovered by a short time of heating treatment. This work could provide a guidance for developing durable under-liquid superlyophobic materials with self-healing ability for diversified applications, such as liquid separation, micro-fluid manipulation, anti-adhesive surfaces.

Simulation of multiphase behavior in supercritical CO2–heavy oil–water sludge extraction systems using Cubic-Plus-Association Equation of State

A new methodology was proposed for predicting the multiphase behavior of a supercritical CO2–heavy oil–water–solvent system during supercritical CO2 extraction. The cubic-plus-association equation of state (CPA EoS) was used to model the hydrogen bond association between asphaltene and water and to develop a nine-step characterization method for asphaltene-containing oil. Results showed that the proposed method could represent phase behavior for three equilibrium phases: the vapor phase and high-density and low-density liquid phases. The absolute average relative deviation between the predicted and experimental phase boundary pressures was 3.6–11.8%, smaller than those (7.0–20.8%) calculated using Soave–Redlich–Kwong EoS with Huron–Vidal mixing rules. Moreover, case studies on appropriate extraction conditions showed that the extraction pressure increased with increasing molecular weight and critical pressure of each pseudocomponent. Increasing extraction pressure for H2O-containing systems was beneficial for improving extraction efficiency.

A Nano Needle-like Hydrophobic Co3O4@SSM for Heavy Oil Water Separation with High Efficiency

The needles-like Co3O4 with micro nano structure was synthesized by hydrothermal method and calcination. After being modified by octadecyl mercaptan, it shows an ultra-high separation efficiency of more than 99.9% for Dichloromethane, 1,2-Dichloroethane and Trichloromethane oil/water mixtures. We believe this metal- based separation membrane will provide significant reference for further practical research. The Co3O4 with the needles-like micro nano structures is generated on stainless steel mesh by hydrothermal method and calcination, and then modified by octadecylmercapta(ODT), which changed Co3O4 structure from hydrophilic wettability to nearly superhydrophobicity. The Co3O4@SSM shows excellent heavy oil-water separetion eefficiency to three different kinds (dichloromethane, 1,2-dichloroethane and trichloromethane) of heavy oil/water mixture for 10 cycles.

Study on the emulsification characteristics of heavy oil during chemical flooding

Chemical flooding is a very important method to the efficient development of a heavy oil reservoir. A clear understanding of the relationship between emulsification characteristics of heavy oil during chemical flooding and test methods that current used to evaluate the properties of chemical flooding agent can be useful for oilfields development of the heavy oil. In this study, the oil–water interfacial tension (IFT) and oil in water (O/W) emulsion properties (emulsification state, droplet size, viscoelasticity, and stability) formed by six chemical flooding agents at different concentration are tested. Then, combined with the heavy oil flooding dynamics, the emulsification characteristics of heavy oil during the chemical flooding process of are studied and the influence mechanisms of O/W emulsion on oil recovery are clarified. Finally, the emulsification effect of heavy oil on the injection profile turnover is studied by parallel sand-packed tube experiments. Studies show that all six chemical flooding agents can greatly reduce the IFT of heavy oil–water (more than 90%). However, the stronger the emulsification ability, the smaller the droplet size, the better the viscoelasticity, the stronger the stability of O/W emulsion, and the better the heavy oil recovery of the chemical flooding agent. This is mainly because the most effective action stage is the time that before the O/W emulsion front flow reaches the production outlet, chemical flooding agent is injected into the formation. During this period, the amount of emulsified heavy oil, the width of emulsification zone, and the properties of formed O/W emulsion affect the heavy oil flooding efficiency. Therefore, when screening chemical flooding agents, the emulsification speed, the droplet size, and the viscoelasticity of formed O/W emulsion are the primary evaluation factors. In addition, through the parallel sand-packed tube experiment, it is found that the stronger the emulsification ability of chemical flooding agent, the better the performance of formed O/W emulsion, the stronger the profile turnover ability. For reservoirs that the water flow channel has formed, using profile control agents to effectively block dominant flow channels can improve the emulsification ability of chemical flooding agents, thus achieving the purpose of improving the swept area. The research results can provide guidance for the screening of chemical flooding agent with emulsification characteristic and construction process optimizing in the heavy oil reservoirs' development.

Transfer-Printed Environmental-Friendly Anisotropic Filter with Laser-Controlled Micropores for Efficient Oil/Water Separation

Water is indispensable for sustaining life on Earth. Oil–water mixtures/or emulsions from industrial waste and other sources are a serious environmental concern for both human beings and aquatic life. Specially treated meshes and textiles with opposing wettability for oil–water separation have been widely reported as a solution to this challenge. Nonetheless, such membranes are hindered by certain drawbacks, including high manufacturing costs, usage of harmful chemicals, and lack of diverse applicability. Here, we report a facile method to fabricate Janus oil–water separation membrane with a controllable pore structure that has a unique directional flux rate. The superhydrophobic (SHB) layer of the membrane is formed by transfer-printing (TP) carbon soot particles onto a polydimethylsiloxane (PDMS)-coated paper surface. Meanwhile, a spin-coated thin layer of chitosan on the other side of the film served as a hydrophilic (SHL) and underwater oleophobic face. A pulsed laser beam is used to produce micropores with conical structures. The separation ability of the membrane for both light oil–water and heavy oil–water mixtures is thoroughly investigated. Moreover, the significance of the pore shape and the size is also elucidated. The flexible Janus membrane showed high thermal stability and ideal (i.e., 99.8%) separation efficiency. The membrane can be produced over a 151 cm2 size range. Besides having flexibility and superior performance, the fabricated membrane is environmentally friendly and economically viable. This work establishes a scalable basis for efficient and low-cost oil/water membranes from non-porous substrates.

Modification of sisal cellulose (Agave sisalana) with poly(vinyl alcohol) and its evaluation in a water-heavy oil system

Cellulose is a natural, non-toxic and biodegradable polymer that can have its structure modified to give it the desired properties. This study aimed to modify sisal cellulose (Agave sisalana) from its xanthate with poly (vinyl alcohol) (PVA) and to evaluate its viscosifying action on the flow behavior of a water-heavy oil system for petroleum production, on a laboratory bench. The modified process was carried out by graphitization and monitored by FTIR. The viscosifying potential was evaluated by measuring intrinsic degrees and the action of modified sisal cellulose (CSM) in the water-heavy oil system was gradually evaluated, at temperatures of 25°C and 60°C, using a brookfield viscometer. The FTIR spectra confirmed the modification by the appearance of the wavenumber band 880 cm-1, indicating the occurrence of the substitution reaction of [–OH] groups of the C-6 of the cellulose structure. The rate of the water-heavy oil system with the CSM was equal to the graduation of the heavy oil, with the same flow activation energy (Ea) in the amount of 66,509 kJ/mol, which gave potential use of the CSM in the correction of the profile of result of the system under study

A molecular dynamics simulation on dissolution of subcritical water in heavy oil: (I) Effect of polycyclic aromatic hydrocarbons

Molecular dynamics simulations were applied to characterize the dissolution of subcritical water (Sub-CW) in polycyclic aromatic hydrocarbons (PAHs). The phase equilibria of Sub-CW/PAHs are characterized by the dissolution of Sub-CW in PAHs.The solubility of Sub-CW increases with temperature but is relatively insensitive to pressure changes. Furthermore, an increase in PAH scale leads to a decrease in Sub-CW solubility. The PAH-rich phase can be divided into an interface region and a bulk region, and the water concentrations in the two regions differ greatly. The Hansen solubility parameters of PAHs and Sub-CW exhibit opposite distributions, hindering the mutual solubility between the two. The dissolution of Sub-CW is promoted by the destruction of intermolecular hydrogen bonds of water at increasing temperature, but is ultimately inhibited by the difference in dispersion properties between PAHs and Sub-CW. According to the Gibbs solvation free energy, the electrostatic interaction between PAHs and Sub-CW favors the dissolution of Sub-CW. Meanwhile, the van der Waals interaction shows different effects.