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Carbon dioxide flooding is a strategic replacement technology for greatly enhancing oil recovery in low-permeability oilfields, which includes social benefits resulting from carbon emission reduction and economic benefits owing to the improvement of oil recovery. Therefore, it is of great significance to develop and apply the technology of CO2 flooding and storage in the petroleum industry. In reservoir conditions, CO2 is usually under a supercritical state, presenting both low viscosity and high diffusivity of a gaseous state and high density of a liquid state. The special phase behavior of CO2 directly affects its extraction capacity, resulting in the change of miscible behavior between CO2 and crude oil. In this paper, the ultra-high-pressure–high-temperature pressure–volume–temperature (PVT) system was used to evaluate the phase characteristics of CO2 during the process of reservoir development. The phase behaviors of the CO2/CH4/N2 crude oil system were compared and analyzed. Moreover, the matching mechanism between supercritical CO2 characteristics and oil–gas system miscibility was investigated and defined. This work deepened the understanding of the phase characteristics of CO2 in the process of miscible flooding, providing both theoretical guidance for the application of CO2 injection on oilfields and the essential scientific basis for the implementation of CCUS-EOR technology. [ABSTRACT FROM AUTHOR]

Because of the growing demand for energy, oil extraction under complicated geological conditions is increasing. Herein, oil displacement by CO2 in wedge-shaped pores was investigated by molecular dynamics simulation. The results showed that, for both single and double wedge-shaped models, pore Ⅱ (pore size from 3 to 8 nm) exhibited a better CO2 flooding ability than pore Ⅰ (pore size from 8 to 3 nm). Compared with slit-shaped pores (3 and 8 nm), the overall oil displacement efficiency followed the sequence of 8 nm > double pore Ⅱ > single pore Ⅱ > 3 nm > double pore Ⅰ > single pore Ⅰ, which confirmed that the exits of the wedge-shaped pores had determinant effects on CO2 enhanced oil recovery over their entrances. "Oil/CO2 inter-pore migration" and "siphoning" phenomena occurred in wedge-shaped double pores by comparing the volumes of oil/CO2 and the center of mass. The results of the interaction and radial distribution function analyses indicate that the wide inlet and outlet had a larger CO2–oil contact surface, better phase miscibility, higher interaction, and faster displacement. These findings clarify the CO2 flooding mechanisms in wedge-shaped pores and provide a scientific basis for the practical applications of CO2 flooding. [ABSTRACT FROM AUTHOR]

The development of high-performance CO2 capture and separation adsorbents is critical to alleviate the deteriorating environmental issues. Herein, N atom-doped layered graphene (N-MGN) was introduced to form triazine and pyridine as potential CO2 capture and separation adsorbents via regulation of interlayer spacings. Structural analyses showed that accessible surface area of the N-MGN is 2521.72 m2 g−1, the porosity increased from 9.43% to 84.86%. At ultra-low pressure, N-MGN_6.8 have exhibited a high CO2 adsorption capacity of 10.59 mmol/g at 298 K and 0.4 bar. At high pressure, the absolute adsorption capacities of CO2 in N-MGN_17.0 (40.16 mmol g−1) at 7.0 MPa and 298 K are much larger than that of N-doping slit pore. At 298 K and 1.0 bar, the highest selectivity of CO2 over N2 reached up to ~133 in N-MGN_6.8. The research shows that N doping can effectively improve the adsorption and separation capacity of CO2 and N2 in layered graphene, and the interlayer spacing has an important influence on the adsorption capacity of CO2/N2. The adsorption heat and relative concentration curves further confirmed that the layered graphene with an interlayer spacing of 6.8 Å has the best adsorption and separation ability of CO2 and N2 under low pressure. Under high pressure, the layered graphene with the interlayer spacing of 17.0 Å has the best adsorption and separation ability of CO2 and N2. [ABSTRACT FROM AUTHOR]

The adsorption mechanism of the branched quaternary ammonium salt Gemini surfactant (Gemini C3) at the water-surfactant-quartz interfaces for both neutral and negatively charged quartz surfaces was studied by a molecular dynamics (MD) method. Initial and final configurations, distributions of the surfactant and its interaction with surfaces, the radial distribution function (RDF) of water molecules, and the mean square displacement (MSD) of the surfactant in bulk phase have been elucidated at the molecular level. The results showed that the adsorption of Gemini surfactants onto the hydrophilic quartz surface was driven by electrostatic interaction, which increased the hydrophobicity of the solid surface when the surfactant concentration was lower than critical micelle concentration (CMC). However, the contact angle only slightly increased since the surface tension decreased simultaneously with growing concentration. Monolayers were formed during the adsorption process of Gemini C3 molecules on the quartz surface rather than a double layer when the concentration reached the CMC, indicating a gradual transformation of an extended monolayer adsorption configuration into a more compact one. The solid-liquid interfacial tension increased with the surfactant concentration and led to a significant increase of the contact angle. The simulation results were consistent with the experiments, which further revealed the microscopic adsorption mechanism of the Gemini C3 surfactant onto the quartz surface, and provided theoretical guidance for controlling the wetting properties and surface modification of the rock. The adsorption mechanism of the branched quaternary ammonium salt Gemini surfactant (Gemini C3) at the water-surfactant-quartz interfaces for both neutral and negatively charged quartz surfaces was studied by Molecular Dynamics (MD) method. [ABSTRACT FROM AUTHOR]

Rapid 3D radiation field evaluation is the key point of occupational dose optimization for design and operation of nuclear power plant. Based on the requirement analysis from designers and operators of nuclear power plant, three key technical issues are identified and solved through the development of the RPOS system, which are rapid calculation of 3D radiation field, reconstruction of the calculated 3D radiation field based on measured data, and occupational dose optimization based on 3D radiation field. Operational measurements of dose rate from in-service nuclear power plants are used to test the RPOS system, which shows that accurate 3D radiation field can be rapidly generated by the RPOS system and effectively used on the occupational dose optimization for on-site workers. The applications of the established rapid 3D radiation field evaluation technique on HPR1000 unit design provide evidence on its feasibility in a large scale, the improvement of radiation protection design efficiency and the enhancement of ALARA assessment and justification for nuclear power plants. [ABSTRACT FROM AUTHOR]

CO2 flooding is a pivotal technique for significantly enhancing oil recovery in low-permeability reservoirs. The movement and sweeping rules at the front of CO2 flooding play a critical role in oil recovery; yet, a comprehensive quantitative analysis remains an area in need of refinement. In this study, we developed 1-D and 2-D numerical simulation models to explore the sweeping behavior of miscible, immiscible, and partly miscible CO2 flooding patterns. The front position and movement rules of the three CO2 flooding patterns were determined. A novel approach to the contour area calculation method was introduced to quantitatively characterize the sweep coefficients, and the sweeping rules are discussed regarding the geological parameters, oil viscosity, and injection–production parameters. Furthermore, the Random Forest (RF) algorithm was employed to identify the controlling factor of the sweep coefficient, as determined through the use of out-of-bag (OOB) data permutation analysis. The results showed that the miscible front was located at the point of maximum CO2 content in the oil phase. The immiscible front occurred at the point of maximum interfacial tension near the production well. Remarkably, the immiscible front moved at a faster rate compared with the miscible front. Geological parameters, including porosity, permeability, and reservoir thickness, significantly impacted the gravity segregation effect, thereby influencing the CO2 sweep coefficient. Immiscible flooding exhibited the highest degree of gravity segregation, with a maximum gravity segregation degree (GSD) reaching 78.1. The permeability ratio was a crucial factor, with a lower limit of approximately 5.0 for reservoirs suitable for CO2 flooding. Injection–production parameters also played a pivotal role in terms of the sweep coefficient. Decreased well spacing and increased gas injection rates were found to enhance sweep coefficients by suppressing gravity segregation. Additionally, higher gas injection rates could improve the miscibility degree of partly miscible flooding from 0.69 to 1.0. Oil viscosity proved to be a significant factor influencing the sweep coefficients, with high seepage resistance due to increasing oil viscosity dominating the miscible and partly miscible flooding patterns. Conversely, gravity segregation primarily governed the sweep coefficient in immiscible flooding. In terms of controlling factors, the permeability ratio emerged as a paramount influence, with a factor importance value (FI) reaching 1.04. The findings of this study can help for a better understanding of sweeping rules of CO2 flooding and providing valuable insights for optimizing oil recovery strategies in the field applications of CO2 flooding. [ABSTRACT FROM AUTHOR]

The carbon capture, utilization and storage (CCUS) technique is widely applied in order to solve energy shortages and global warming, in which CO2 storage plays an important part. Herein, the CO2 storage in reservoir pores with a dead-end is investigated using a molecular dynamics simulation. The results indicate that, when a CO2 molecule flows through a reservoir pore towards its dead-end, it is readily captured inside said dead-end. When the pressure difference of the CO2 injection increases, the transport speed of the CO2 becomes faster, and the storage efficiency increases. The rate constants for the absorption of the carbon dioxide at 5 MPa, 10 MPa, and 15 MPa are 0.47 m/s, 2.1 m/s, and 3.1 m/s. With the same main channel, a narrower dead-end with less oil molecules would cause a smaller spatial potential resistance, which would lead to a faster CO2 replacement and storage process. The 3 nm main channel with a 1.5 nm dead-end model had the highest absorption rate of 5.3 m/s out of the three sets of models with different dead-ends. When the dead-end's width was constant, the rate constants for the absorption of carbon dioxide in the 6 nm main channel with a 1.5 nm dead-end model was 1.8 m/s, which was higher than that of the 3 nm–1.5 nm model. This study investigates the mechanism of CO2 storage in reservoir pores with a dead-end at the molecular level and provides a scientific basis for the practical application of CO2 storage. [ABSTRACT FROM AUTHOR]

The occurrence state of oil, gas, and water plays a crucial role in exploring shale reservoirs. In this study, molecular dynamics simulations were used to investigate the occurrence states of these fluids in shale nanopores. The results showed that when the alkane is light oil, in narrow pores with a width less than 3 nm, oil molecules exist only in an adsorbed state, whereas both adsorbed and free states exist in larger pores. Due to the stronger interaction of water with the rock surface, the adsorption of oil molecules near the rock is severely prohibited. Oil/water/gas occurrence characteristics in the water-containing pore study indicate that CO2 gas can drive free oil molecules out of the pore, break water bridges, and change the occurrence state of water. During displacement, the gas type affects the oil/gas occurrence state. CO2 has strong adsorption capacity, forming a 1.45 g/cm3 adsorption layer on the rock surface, higher than oil's density peak of 1.29 g/cm3. Octane solubility in injected gases is CO2 (88.1%) > CH4 (76.8%) > N2 (75.4%), with N2 and CH4 having weak competitive adsorption on the rock. The investigation of different shale reservoir conditions suggests that at high temperature or low pressure, oil/gas molecules are more easily displaced, while at low temperature or high pressure, they are tightly adsorbed to the reservoir rock. These findings contribute to the understanding of fundamental mechanisms governing fluid behavior in shale reservoirs, which could help to develop proper hydrocarbon recovery methods from different oil reservoirs. [ABSTRACT FROM AUTHOR]

A ternary memristor full adder is designed based on the literal operation and module‐3 plus operation. Literal operation and module‐3 plus operation are the important operations in the tri‐valued algebra system. Multiple‐valued logic can increase the amount of information carried by the signals and reduce the number of devices and connections. The combination of multiple‐valued logic and memristor is an exploration of new devices and new structures. The novel ternary memristor full adder owns the advantage of simpler structure without decoding units to convert ternary signals to binary at the terminals, and all the signals operated by the circuit are ternary. Compared with the traditional ternary full adder, the number of devices and the power consumption are greatly reduced. Simulation results of different memristor models verified the correctness and applicability of the circuit design. It provides a new idea for the design method of memristor circuits, especially multiple‐valued memristors. [ABSTRACT FROM AUTHOR]

Recently, most multiple object tracking (MOT) algorithms adopt the idea of tracking-by-detection. Relevant research shows that the performance of the detector obviously affects the tracker, while the improvement of detector is gradually slowing down in recent years. Therefore, trackers using tracklet (short trajectory) are proposed to generate more complete trajectories. Although there are various tracklet generation algorithms, the fragmentation problem still often occurs in crowded scenes. In this paper, we introduce an iterative clustering method that generates more tracklets while maintaining high confidence. Our method shows robust performance on avoiding internal identity switch. Then we propose a deep association method for tracklet association. In terms of motion and appearance, we construct motion evaluation network (MEN) and appearance evaluation network (AEN) to learn long-term features of tracklets for association. In order to explore more robust features of tracklets, a tracklet-based training mechanism is also introduced. Tracklet groups are used as the input of the networks instead of discrete detections. Experimental results show that our training method enhances the performance of the networks. In addition, our tracking framework generates more complete trajectories while maintaining the unique identity of each target as the same time. On the latest MOT 2017 benchmark, we achieve state-of-the-art results. [ABSTRACT FROM AUTHOR]