Kinetic hydrate inhibitors (KHIs) have shown significant potential in preventing hydrate blockages and ensuring flow assurance by delaying hydrate nucleation and aggregation. However, the molecular mechanisms by which KHIs influence the early-stage growth and stability of hydrate fluids under oil and gas flow conditions remain insufficiently understood, limiting the optimization and development of more efficient formulations. In this paper, molecular dynamics (MD) simulations were employed to systematically investigate the regulatory effects of two representative KHIspolyvinylpyrrolidone (PVP) and polyvinylcaprolactam (PVCap)on gas hydrate prevention; and the interaction mechanism between the molecules was elucidated by combining molecular dynamics simulations with Density Functional Theory (DFT). Key parameters, including the number of cage structures, the water molecule ordering parameters, and the potential energy, were also analyzed to assess the inhibitors' impacts on gas hydrate growth and fluid stability. The results reveal a triple synergistic mechanism involving site-blocking, mass transfer interference, and hydrogen-bond disruption, which provides a theoretical basis for the design and optimization of high-efficiency KHIs in the traditional fossil fuel transportation, particularly in oil and gas flowlines.

Oil-based drilling cuttings (OBDCs) are typical hazardous solid wastes due to their strong mutagenic, carcinogenic, and teratogenic properties. Herein, a pH-switchable hydrophobic deep eutectic solvent (HDES) based on branched-chain fatty acids was developed, using 2-ethylhexanoic acid (EHA) as the hydrogen bond donor (HBD) and valproic acid (PPA) as the hydrogen bond acceptor (HBA), along with a feasible approach to the efficient treatment of OBDC. It was found that NaOH/HCl solutions triggered the deprotonation and protonation of the -COOH groups in HDES, enabling a reversible transformation of HDES from hydrophobicity to hydrophilicity. Interestingly, HDES featured a remarkable antiemulsifying property attributed to its short-branched-chain structure, which intensified the separation capacity of simulated oils (heptane, kerosene, and white oil). The pH-induced separation efficiency of the simulated oils reached 99%. Due to these unique properties, the usage of HDES for cleaning OBDC was demonstrated. The first and fourth oil removal rates of HDES respectively reached 98.41 and 87.04% by tailoring the PPA to EHA molar ratio of HDES to 1:2. Correspondingly, after being alternately triggered by NaOH/HCl solutions, 88.89 and 72.13% of HDES were recovered in the first and fourth cleaning processes. HDES is expected to be a promising alternative for the resource utilization of OBDC due to its lower volatility and toxicity compared with traditional solvents. We postulate that the proposed HDES has great promise for the reduction, resource utilization, and harmless treatment of oily solid waste.

To manage the interactions between wax and hydrate formation, a comprehensive understanding of the system's thermodynamics and flow characteristics is essential. Wax and hydrates coexist under low-temperature and high-pressure conditions, mutually influencing each other both thermodynamically and kinetically. This study focused on two main aspects: how wax affects the rate of hydrate formation in the oil-water system and how hydrate formation influences the thermodynamics of wax crystal precipitation. The presence of wax decreased the rate of hydrate formation, especially at higher wax contents. In systems with high wax content, over 70% of wax precipitated before hydrate formation, leading to less precipitation within the hydrate formation temperature range. With low water content, there were more nucleation sites for wax crystals in the oil phase, resulting in a greater difference in precipitation rates among different wax contents. For water content greater than 10%, the differences in precipitation rates were less significant, indicating a diminished effect of water content on wax crystal precipitation rates. Hydrates' hydrophilic nature had a limited impact on wax crystal nucleation and growth. Generally, wax crystals precipitate before hydrate formation, necessitating control measures for wax deposition during production processes.

To facilitate the recovery of natural gas hydrate（NGH） deposits in the South China Sea, we have designed and developed the world's largest publicly reported experimental simulator for NGH recovery. This system can also be used to perform CO 2 capture and sequestration experiments and to simulate NGH recovery using CH 4 /CO 2 replacement. This system was used to prepare a shallow gas and hydrate reservoir, to simulate NGH recovery via depressurization with a horizontal well. A set of experimental procedures and data analysis methods were prepared for this system. By analyzing the measurements taken by each probe, we determined the temperature, pressure, and acoustic parameter trends that accompany NGH recovery. The results demonstrate that the temperature fields, pressure fields, acoustic characteristics, and electrical impedances of an NGH recovery experiment can be precisely monitored in real time using the aforementioned experimental system. Furthermore, fluid production rates can be calculated at a high level of precision. It was concluded that（1） the optimal production pressure differential ranges from 0.8 to 1.0 MPa, and the wellbore will clog if the pressure differential reaches1.2 MPa; and（2） during NGH decomposition, strong heterogeneities will arise in the surrounding temperature and pressure fields, which will affect the shallow gas stratum.

Permeability is a key parameter to characterize fluid flow in hydrate-bearing sediments. Figuring out dynamic permeability evolution is of great importance for the effective development of hydrate-bearing deposits. In this paper, a grain-coating hydrate-bearing regular pore network model with complex pore throat cross-sections is first constructed. Afterward, the dynamic permeability evolution regularity is calculated. After the validation, the effects of initial aspect ratio, coordination number, and pore throat cross-sections on dynamic permeability evolution are investigated. The results show that hydrate narrows the effective flow space, which results in the exponential decrease of dynamic permeability with the increased hydrate saturation. The larger initial aspect ratio aggravates the heterogeneity of the pore network, resulting in a faster permeability decline rate. However, hydrate weakens the effect of initial aspect ratio on dynamic permeability evolution since the physical hydrate thickness in large pore bodies and throats is larger. The high initial coordination number reduces the dynamic permeability decline rate with the increased hydrate saturation since the higher coordination number increases the topology of the network, while hydrate compresses or blocks the effective pore throat space. Pore throat cross-sections have nothing to do with dynamic permeability evolution, but they dramatically influence the absolute permeability values. This study provides a novel insight into dynamic permeability evolution in hydrate-bearing sediments.

Paraffin wax has caused obvious detrimental consequences to the extraction for fossil fuels, and posed envi-ronmental challenge due to the absence of cleaner methods for paraffin wax removal. A cleaner and sustainable approach for paraffin wax removal was developed using the switchable polarity solvents (SPS). Three SPS with low polarity, including dipropylamine (DPA), ethylbutylamine (EBA), and dibutylamine (DNBA) were selected for paraffin wax removal. Compared with bubbling CO2 into SPS straightway, the transformation of the polarity quantified by normalized polarity energy confirms the addition of water is benefit to enlarge the polarity scope. Paraffin wax is removed at the initial state and separated at the final state by CO2-induced polarity trans-formation of SPS. The dissolution rates for paraffin wax of DPA and EBA reached 0.071 g/min and 0.062 g/min, which surpassed that of traditional solvents, such as o-xylene (0.045 g/min) and Petroleum ether (0.017 g/min), indicating that these selected SPS is suitable for paraffin wax removal. The paraffin wax dissolution behaviors of SPS can be accurately matched using modified Apelblat models with root-mean-square deviation of 1.085%. With the addition of water, more than 99% of paraffin wax is separated from DPA and EBA by introducing CO2 within 10mins, which is a better alternative method for energy-intensive distillation process. The introduction of water is indispensable for improving the separation efficiency, since it enlarged the polarity difference between sol-vents and paraffin wax. The thermal behavior of separated paraffin wax detected by Differential Scanning Calorimetry remained steady, and there were negligible residual solvents detected indicate the feasible sepa-ration of paraffin wax. Both SPS and water are recovered upon N2/80 degrees C, which retain good recyclability for paraffin wax removal. These findings confirms the applicability of SPS in the sustainable and cleaner removal of paraffin wax. The use of SPS provides an alternative and promising approach for paraffin wax removal for ensuring the demands of low-energy consumption and environment.

Hydrate spatial distribution plays an important rolein dynamicpermeability evolution in the development of hydrate-bearing sediments.In this work, an irregular pore network model with complex pore throatcross sections and anisotropy is first generated. Afterward, the hydratespatial distribution is classified into four patterns and assignedto the established network in the grain-coating mode from large poresto small ones gradually. After the validation, impacts of the hydratespatial distribution on the effective pore throat radii distributionare investigated in terms of the hydrate-bearing pore network. Furthermore,dynamic permeability evolution in different hydrate spatial distributionmodes is studied in detail. Results show that the hydrate spatialdistribution has a significant effect on dynamic permeability evolutionby influencing the effective size distribution of pore bodies andthroats. This study provides a novel insight into dynamic permeabilityevolution at different hydrate spatial distributions, laying a solidfoundation for the efficient development of hydrate-bearing deposits.

Wax precipitation leads to destructive harms in the exploitation and transportation of petroleum. Solvent treatments can remove paraffin wax easily but the separation of solvent relying on distillation is admitted inefficient. Aiming at enhancing the separation and recovery performance of paraffin wax, CO2-responsive emulsion (SHS/W emulsion) based on switchable hydrophilicity solvents (SHS) is adopted. Since the paraffin wax is dissolved, emulsified, and dispersed by SHS/W emulsion, SHS/W emulsion exhibits better removal performance than SHS. The paraffin wax is recovered effectively upon introducing CO2, which attributes to the transformation of SHS from hydrophobic to hydrophilic state. Compared with the SHS system, the recovery of paraffin wax is improved obviously by introducing surfactant Span80. Owing to the deprotonation of SHS by bubbling N2 and heating, 77.6% SHS is recycled after recovering paraffin wax. Here, the recycled SHS can be used to realize the removal of paraffin wax again. Thus, it is a promising and alternative strategy for realizing the sustainable and rapid removal of paraffin wax in the petroleum industry.

The insufficient heat supply during gas production from hydrate reservoir significantly hinders the efficiency of hydrate exploitation. The effective thermal conductivity (ETC) of hydrate bearing sediment has been recognized as an effective indicator of the heat transfer process. Yet its evaluation could be coupled with the phase transition and components migration; the relevant knowledge on its dependence on the phase transition of gas hydrate in clay sediments still remains limited. Here in this work, a point-heat-source based instrument was used to investigate the change of ETC in fine-grained sediment during ice melting, hydrate formation and decomposition. The result shows that the ETC declined during ice melting and hydrate decomposition; hydrate formation could result in an increase of ETC. The decomposition water in pores could partly facilitate the heat transfer in porous media. Samples with the initial water saturation higher than 18% were more easily affected by hydrate formation and decomposition; this indicates that hydrate reservoir with a high water saturation could face a more varying capacity of heat transfer. The hydrate samples of deionized water and brine water system with similar saturation of nongaseous phase shows a similar behavior of ETC during phase transition. Moreover, typical effective me-dium model was evaluated with our measured data. A thermal resistance model based on the real distribution of phases in hydrate bearing sediment was proposed; its feasibility was verified by our measured data and those of in-house and field tests in the literature. This study could provide some insight into the energy supply during hydrate exploitation and the enhancement of the gas production process.

The Qiongdongnan Basin is an important gas hydrate exploration area in the South China Sea, but the gas hydrate accumulation process is poorly understood. By selecting an Lingshui (LS) target area and using first-hand geochemical data, three-dimensional seismic data, and an independent thermal insulation and pressure maintaining shipborne core analysis system, in this study, comprehensive geological evaluation was carefully conducted around the gas source and reservoir of the gas chimney hydrates, and the accumulation process was investigated. Geochemical data for a total of 47 sets of gas samples revealed that the gas source of the hydrates in the study area was mainly thermogenic gas supplemented by mixed gas. It was predicted that the contribution of the thermogenic gas to the hydrate accumulation was up to 70%. Using the independent shipborne core analysis system, the characteristics of the low-temperature combustible gas hydrates were determined, and the reservoir in the study area was characterized as non-diagenetic to weakly diagenetic, rich in clay and silt (D50 = 15.1–34.1 μm), weakly self-sustaining, and strongly heterogeneous. Based on the differentiated seismic response of the hydrate layer-gas bearing hydrate layer-shallow gas layer at the top of the gas chimney, the accumulation process in the target area was determined to be as follows: remote thermogenic gas transportation, local microbial genetic gas accumulation, episodic dynamic gas chimney reservoir formation, and source-reservoir control. In addition, the exploration ideas of an effective supply from a gas source and a shallow large-scale sand body are emphasized. The results of this study provide an important reference for the trial production of natural gas hydrates in the South China Sea.

Tertiary amines (TA) are widely treated as the responsive additions of stimuli-responsive emulsion. The effect of alkane carbon number (ACN) of TA (N,N-Dimethyldecylamine (DMA), N,N-Dimethyldodecylamine (DMDA), N,N-Dimethyltetradecylamine (DMTA) and N,N-Dimethylhexadecylamine (DMHA)) on redox and pH- responsive behavior of emulsion was explored, obtaining a reference to regulate the redox and pH- responsiveness of emulsion precisely. Here, the emulsions are stabilized by the surfactant prepared simply with electrostatic interaction TA and ferrocenecarboxylic acid (FA). The stability of emulsion can be enhanced because of the enhanced surface activity of surfactant with increasing ACN of TA, which was demonstrated by the measurement of water separation ratio (WSR), micrographs and Zeta potential value of emulsion. In addition, by the analysis of micrographs, surfactant tension and interfacial tension, it is demonstrated that the more complete oil-water separation is regulated reversibly because of the larger change value of interfacial tension with increasing ACN upon the alternate addition of Na2SO3 and H2O2. Besides, the emulsions stabilized by surfactant prepared with TA containing ACN = 10 and 12 exhibit doubly pH-responsive behavior, which is ascribe to the inactivation of surface activity of surfactant at lower and higher pH. However, the emulsions stabilized by surfactant prepared with TA containing ACN = 14 and 16 exhibit single pH-responsive behavior because of the inactivatd surface activity of surfactant at higher pH and activatd surface activity of protonated DMTA and DMHA at lower pH.

The methodology of using CO2 to replace CH4 to recover the natural gas hydrates (NGHs) is supposed to avoid geological disasters. However, the reaction path of the CH4–CO2 replacement method is too complex to give satisfactory replacement efficiency. Therefore, this study proposed a thermochemical reaction system that used the heat and the nitrogen released by the thermochemical reactions to recover NGHs. The performance of the thermochemical reaction system (NaNO2 and NH4Cl) regarding heat generation and gas production under low temperature (4°C) conditions was evaluated, and the feasibility of exploiting NGHs with an optimized formula of the thermochemical reaction system was also evaluated in this study. First, the effects of three catalysts (HCl, H₃PO₄, and NH2SO3H) were investigated at the same reactant concentration and catalyst concentration. It was confirmed that HCl as a catalyst can obtain better heat generation and gas production. Second, the effect of HCl concentration on the reaction was investigated under the same reactant concentration. The results showed that the higher the HCl concentration, the faster is the reaction rate. When the concentration of HCl was greater than 14 wt%, side reactions would occur to produce toxic gas; hence, 14 wt% was the optimal catalyst concentration for the reaction of NaNO2 and NH4Cl at low temperatures. Third, the heat generation and gas production of the thermochemical reaction systems were evaluated at different reactant concentrations (1, 2, 3, 4, 5, and 6 mol/L) at 14 wt% HCl concentration. It was found that the best reactant concentration was 5 mol/L. Finally, the feasibility of exploiting NGHs with the optimal system was analyzed from the perspectives of thermal decomposition and nitrogen replacement. The thermochemical reaction system provided by this study is possible to be applied to explore NGHs’ offshore.

双碳战略目标下煤炭行业高质量发展迎来新的机遇与挑战,充分释放废弃矿井负碳增能潜力,创新风、光、水、热等新能源开发利用耦合新型物化储能协同发展模式,推进绿色循环低碳能源体系稳定发展.应对清洁能源稳定供给与煤炭工业净零发展挑战,提出废弃矿井绿色低碳多能互补体系,集成全息地质结构重构、多种能源融合、物化联合储能、碳固结利用、多网智慧调控、智能应急救援的产-储-固智慧新型负碳绿色能源供储体系,以地表地下联合空间为载体,多源数据融合数字孪生技术为支撑,风险智能判识预警与灾害应急救援为保障,实现废弃矿区多维度分级分类分区域联动清洁能源生产、储备、供给与碳捕集、封存、利用.凝练了废弃矿井绿色低碳多能互补体系发展面临的数字工程地质、多场时空耦合演化、功能地层空间维稳、风险超前精准预警和智能应急抢修救援等5个关键科学问题,提出了数字孪生工程原态场景、工程扰动多场耦合灾变演化、创新多能互补技术体系、CO2工程封存与生态碳汇、分布式智能电网建设、数字风险预警系统和应急救援技术装备等7个主要研究方向,将为实现清洁能源稳续供给、碳永久封存、能-碳平衡循环发展,保障国家能源安全与经济社会高质量发展提供新途径.

琼东南盆地深水区具备形成天然气水合物藏的地质条件,是我国海洋天然气水合物两个勘探开发先导示范区之一.本文选取深水区浅表层水合物为研究对象,基于天然气地球化学、稀有气体地球化学分析,开展了其与深部常规天然气藏的对比研究.结果表明:本次研究的浅表层气体碳同位素与深部常规天然气碳同位素的特征类似,气源主要为深部热成因气,生物气的贡献不明显,气体的成因类型为煤型气,推测气源岩为崖城组煤系烃源岩.轻稀有气体Ar同位素组成显示,气源岩和第三系相关;样品中3He/4 He值偏高,指示了部分幔源气的贡献.因此,在富生烃凹陷背景下,讨论深部热成因气对水合物成藏具有重要意义,深部热成因气藏与浅层水合物藏在垂向上可以形成立体的天然气藏,为未来的"多气可采"提供理论支持,也有助于提高深水区天然气水合物矿藏开发的经济性.

In order to improve the comprehensive performance of asphalt-based materials with ballasted track closure layer, this paper uses waste rubber powder and recycled PE to compound modification of asphalt, and through three major index tests, bending beam rheometer tests and dynamic shear rheological tests.the results show that the composite modified asphalt-based materials developed have good high and low temperature properties,and it is recommended to use two combinations of 6% recycled PE-11% recycled rubber powder and 7% recycled PE-15% recycled rubber powder to compound the asphalt.

Abstract In order to solve the problems of slow replacement rate and low degree of substitution in the process of CO2 displacement by natural gas hydrate, a method of chemical reagent-CO2 displacement combined mining experiment was proposed. Taking the thermodynamic methanol inhibitor as an example, three groups of experiments were carried out: critical temperature pressure condition for CH4 decomposition at different methanol concentrations, CH4 hydrate decomposition under the condition of methanol reagent at 30% concentration, and methanol reagent-CO2 combined mining. Experiments show that: (1) The concentration of methanol plays a decisive role in hydrate recovery. Methanol reagent has the property of highly reducing the formation temperature of hydrate. Methanol solution concentration is positively correlated with the critical temperature drop of hydrate decomposition and formation pressure. (2) The methanol solution decomposition of hydrate can be roughly divided into three stages: the initial stage of rapid decomposition, the competitive stage of hydrate decomposition and stable transformation, and the stable stage of decomposition. Through experimental simulation, it is concluded that formation pressure is a direct factor affecting the decomposition ability of methanol reagent to hydrate. By changing formation pressure, the rate of CH4 hydrate recovery can be improved. (3) A higher hydrate decomposition rate can be obtained based on the methanol reagent-CO2 displacement mining method. In the action of the methanol reagent, the subsequent injection of CO2 still promotes the decomposition of CH4, that is, the displacement of CO2 hydrate after the decomposition of the hydrate based on the methanol reagent is feasible. The research results are of great significance especially for large-scale mine test mining of permafrost natural gas hydrate chemical reagent method.

In this work, the approach for separating paraffin wax is proposed by using Span 80 combined with switchable water N,N,N',N'-tetramethyl-1,6-hexanediamine (TMHDA), where the emulsification of paraffin wax can be promoted and paraffin wax is also separated sustainably. Here, the Span 80-containing mixture system exhibits an enhanced emulsification ability and CO2-switchable behavior upon the addition of TMHDA. Then, the paraffin wax is effectively emulsified by this switchable system containing Span 80 and TMHDA. Based on the detection of water separation rate, rheological behavior, and micrographs of emulsified paraffin wax, it is found that the emulsification of paraffin wax can be improved by increasing the paraffin wax content and Span 80 content, and the viscosity of the paraffin wax is reduced after emulsification by this switchable system, which ascribes to the dispersion of wax crystals. In addition, the paraffin wax is separated upon introducing CO2, and the TMHDA solution is recovered upon treating with N-2 at 65 degrees C after separating the paraffin wax. The sustainable separation of paraffin wax results from the aggregation of wax crystals because of the reduced obstruction of oil droplets for wax crystals caused by the high ionic strength and the reduced surface activity of this system upon introducing CO2. Herein, it is expected that this sustainable separation can be applied in deposited wax removal in pipelines of crude oil transport.