Interfacial tension (IFT) critically governs multiphase flow, mass transfer, and wettability within natural and engineered water systems. Understanding its behavior is essential for assessing fluid interactions and CO2 migration during geological carbon sequestration. However, accurate quantification of CO2-brine IFT under insitu reservoir conditions remains challenging due to the coupled effects of pressure, temperature, salinity, and ionic composition. In this study, a data-driven predictive framework integrating pendant-drop experiments with an extensive literature database was developed to characterize CO2-brine IFT under realistic subsurface conditions. Experiments were conducted at 313.15-363.15 K and 7.5-17 MPa using formation water from the South China Sea, complemented by 3,409 data points compiled from previous studies for model training and validation. A Bayesian-optimized XGBoost model achieved excellent agreement with measured data (R2 = 0.985), capturing nonlinear dependencies beyond conventional empirical correlations. SHAP analysis identified pressure as the primary factor influencing IFT, followed by temperature and ionic composition, and revealed distinct temperature-dependent variations even at constant pressure. These results provide advance insights into the water-phase interfacial processes governing CO2 transport and trapping, while the proposed framework offers a scalable, transferable approach for rapid IFT estimation across diverse subsurface and water-energy systems.

To reduce coupled motion responses and mooring-load fluctuations of a deepwater semi-submersible production platform with polyester moorings, this study proposes a damping-enhanced polyester mooring system, in which viscous damper units are arranged at the serial interfaces between upper and lower polyester rope segments. A two-way AQWA-Fortran coupled time-domain framework is developed to simulate nonlinear interactions among platform hydrodynamics, composite mooring-line dynamics, and damper-induced restoring and dissipative forces. The framework is verified through numerical convergence analysis, a zero-damper degenerate baseline case, and a physical scaled-model basin test. Parametric analysis identifies a representative parameter set of kd = 120 kN m−1 and cd = 35 kN s/m, corresponding to an average dissipated power of 2.8–3.0 MW. Free-decay results show that the heave and surge damping ratios increase from 2.2% to 9.3% and from 4.0% to 7.46%, respectively, with little influence on pitch. Under regular and irregular waves, heave, surge, and mooring-line tension fluctuations are reduced by approximately 10%–26%, 5%–9.5%, and 16%–28%, respectively. Annual assessment confirms consistent reductions in platform motions and mooring-load fluctuations. Although mean mooring tension slightly increases, the cyclic tension component and a preliminary, relative fatigue-related damage indicator are significantly reduced.

Vortex-induced vibration (VIV) energy harvesting represents a promising technology for marine renewable energy exploitation. However, practical application of this technology is constrained by critical hydrodynamic challenges. Specifically, the inherent shear of ocean currents results in a decrease in current velocity with increasing depth, necessitating the placement of energy harvesters near the water surface to maximize energy capture efficiency. Nevertheless, wave action exerts a significant influence on the VIV response of such harvesters. Currently, research regarding the effects of wave modulation on the VIV evolution of near-surface horizontal circular cylinders remains limited, and the influences of key wave parameters on vibration amplitude and frequency characteristics remain largely unexplored. Accordingly, a flume experiment was completed. The vibration responses of a near-surface horizontal circular cylinder were investigated under coupled wave-current interactions. Through spectral analysis, the nonlinear modulation effects of wave period and wave height on the VIV of the cylinder are elucidated, particularly across its three distinct response branches (initial, upper, and lower). The results demonstrate that the relationship between the wave period and the natural period of the cylinder governs the wave-induced influence. A consistent wave period induces a synergistic effect with larger vibration amplitudes than current-only conditions at the same reduced velocity. A divergent wave period triggers a competitive mechanism. Wave height modulates the intensity of the synergy or competition between VIV and wave-induced vibration (WIV).

Decarbonizing industrialized coastal regions is essential to achieving global climate targets. This study conducts a comprehensive, multi-level spatial and structural assessment of the energy mix and carbon emission patterns in Guangdong Province, China-one of the most industrialized and energy-intensive regions nationwide. By integrating provincial, municipal, and enterprise-level datasets, we identify the dominant role of the secondary sector in energy consumption and reveal significant spatial disparities in sectoral emissions across cities. Detailed analysis highlights the clustering of major carbon-emitting enterprises, particularly coal-fired power plants, along coastal zones and within the Pearl River Delta (PRD). Despite the deceleration in thermal power growth, coal-fired electricity generation remains the primary emission source, while renewable energy, though rapidly expanding, contributes a relatively modest share. Emission projections for the power sector indicate a gradual decline through the mid-century, contingent on the accelerated deployment of Carbon Capture, Utilization, and Storage (CCUS) technologies, the expansion of renewable energy, and the strategic phaseout of outdated coal capacity. The findings provide critical insights for optimizing source-sink matching in CCUS deployment and inform the design of differentiated, region-specific decarbonization strategies. This study offers valuable empirical evidence to support Guangdong's low-carbon transition and contributes to broader discussions on sustainable energy transformations in rapidly industrializing coastal regions.

CO2 is a major greenhouse gas, and its large-scale emission reduction is crucial for achieving climate goals. CO2 sequestration in marine sediments via the hydrate method is a promising technology. This study employs a sandclay composite porous medium to investigate the coupled effects of water saturation, salinity, and montmorillonite (MMT) content on CO2 hydrate formation kinetics. The results confirm the inhibitory effect of salinity, which notably reduces total CO2 consumption and shifting the kinetic mode to a "delayed-peak" pattern. A low MMT concentration of 0.3 wt% exhibited the best comprehensive performance with a TOPSIS Ci value of 0.84, whereas concentrations of >= 3.0 wt% MMT caused the kinetic rate to drop below 0.15 mmol/min and reduced the final hydrate saturation to its lowest value of 11.17%. Water saturation embodied a trade-off between capacity and efficiency. 100% saturation resulted in higher total consumption, but 50% saturation showed superior kinetics due to its larger gas-liquid interfacial area, with both t90 and t50 being substantially shortened, and a higher water conversion rate, reaching 40.71%. Traditional growth models have limitations in capturing complex twostage behavior, whereas the proposed piecewise Gompertz model achieves higher accuracy (average R2 = 0.9935; RMSE = 2.7380), reducing prediction error by approximately 67% compared with traditional models. The synergistic laws and kinetic model framework established in this study provide a theoretical basis for evaluating and optimizing CO2 sequestration efficiency in clay-bearing reservoirs.

Although particle damping has proven to be an effective passive vibration control technique widely applied across a variety of industries, research on its effectiveness and mechanism for suppressing vortex-induced vibrations (VIV) in marine structures remains unclear. This paper investigates the effects of particle dampers on VIV in different branches of a cylinder, determining rules and mechanisms of vibration suppression through a combination of experimental and theoretical analysis methods. Key conclusions drawn from our study include: 1. Optimal filling ratios vary for different VIV branches, with the highest overall VIV suppression effect at a filling rate of approximately 85 %, resulting in amplitude suppression ratios of 30 %-40 %. 2. Particle dampers exhibit an amplitude modulation effect on VIV, with the ability to excite a vibration mode that has the same frequency as the vortex shedding frequency of stationary cylinders. Furthermore, a parameterized study of particle damping systems is conducted in this paper, based on experimental results and theoretical models. Our findings demonstrate the feasibility of applying particle damping to suppress VIV in marine engineering structures, providing valuable reference for selecting optimal parameters of particle dampers.

The deepwater subsea wellhead(SW)system is the foundation for the construction of oil and gas wells and the crucial channel for operation.During riser connection operation,the SW system is subjected to cyclic dynamic loads which cause fatigue damage to the SW system,and continuously accumulated fatigue damage leads to fatigue failure of the SW system,rupture,and even blowout accidents.This paper proposes a hybrid Bayesian network(HBN)-based dynamic reliability assessment approach for deepwater SW systems during their service life.In the proposed approach,the relationship between the accumulation of fatigue damage and the fatigue failure probability of the SW system is predicted,only considering normal conditions.The HBN model,which includes the accumulation of fatigue damage under normal conditions and the other factors affecting the fatigue of the SW system,is subsequently developed.When predictive and diagnostic analysis techniques are adopted,the dynamic reliability of the SW system is achieved,and the most influential factors are determined.Finally,corresponding safety control measures are proposed to improve the reliability of the SW system effectively.The results illustrate that the fatigue failure speed increases rapidly when the accumulation fatigue damage is larger than 0.45 under normal conditions and that the reliability of the SW system is larger than 94%within the design life.

CO2 hydrate offers a promising strategy for long-term carbon storage in marine sediments. To better understand and ultimately improve hydrate formation efficiency, this study introduces a novel piecewise Gompertz model. Originating from mathematical biology to describe constrained growth, the Gompertz function is a sigmoidal model adept at characterizing the multi-stage growth behavior in hydrate formation. Composite suspensions of montmorillonite (MMT) and L-tryptophan (L-Trp) were used in experiments. The optimal synergistic effect was achieved with 0.3 wt% MMT + 0.3 wt% L-Trp, reducing the induction time to 33.54 +/- 1.77 and increasing gas consumption to 9.05 +/- 0.43 mmol-representing a 75 % improvement over pure water. Although 3.5 wt% NaCl significantly inhibited hydrate formation, the presence of L-Trp mitigated this effect, increasing the TOPSIS closeness index from 0.08 to 0.66, where higher values denote conditions closer to the ideal state. Interfacial and spectroscopic analyses clarified the physicochemical synergy: the strong-to-weak hydrogen-bond area ratio slightly decreased (0.94 +/- 0.01), CO2 solubility peaked at 1.17 +/- 0.05 mol/kg, interfacial tension dropped to 49.14 +/- 1.08 mN/m, and negatively charged tactoids (-24.9 to -31.6 mV) provided abundant nucleation sites. The proposed piecewise Gompertz model outperformed traditional Logistic (R2 = 0.8659, RMSE = 0.3304), Gompertz (R2 = 0.8793, RMSE = 0.3463), and piecewise Logistic (R2 = 0.9610, RMSE = 0.1700) models, achieving R2 = 0.9942 and RMSE = 0.0700. The model captures the transition from nucleation to diffusionlimited growth, offering a robust framework for simulating CO2 hydrate formation. These findings clarify the coupled roles of MMT, L-Trp, and salinity, advancing hydrate-based carbon storage in marine environments.

Multi-degree-of-freedom (multi-DOF) wave energy converters (WECs) may capture more wave energy compared to traditional single-DOF WECs. This study proposes a strongly coupled, parallel-driven multi-DOF WEC, named the 6-UPU WEC, which efficiently harnesses omnidirectional wave energy through a multidimensional moving body driven by six parallel hydraulic cylinder. The focus of this work is on deriving the forces from the hydraulic cylinder PTO system acting on the converter using the Newton-Euler method, and developing a nonlinear, strongly coupled dynamic model of the 6-UPU WEC based on WEC-Sim. Model tests were conducted in a wave tank to verify the validity of the numerical model. Using this numerical model, the motion response, power absorption, and array layout workspace of the 6-UPU WEC were investigated. Results show that at a significant wave height of 0.6 m and a wave period of 3.3 s, the energy capture efficiency of the 6-UPU WEC is improved by 11.5 % compared to a two-DOF WEC. Furthermore, the stability of workspace positions and their potential correlation with power capture were evaluated, indicating that a larger position ratio coefficient corresponds to better energy capture performance. The proposed 6-UPU WEC and the developed numerical model, which accounts for the coupled dynamic behavior of the six hydraulic cylinder. Systems, can provide effective references for the design of other complex multi-DOF WECs.

The deepwater drilling riser system is the most vulnerable part of the offshore drilling operation. Understanding its dynamic response under complex marine environment is crucial for ensuring drilling safety. However, the coupling mechanism between the riser and LMRP/BOPs is not well understood in existing analysis models of riser system dynamic response. In this paper, a theoretical model for the rigid-flexible coupling dynamics of multi-scale riser-LMRP/BOPs-wellhead system is proposed to reveal the coupling mechanism between the riser and LMRP/BOPs. Considering the characteristics of flexible riser and rigid LMRP/BOPs as well as the nonlinear coupling effect between conductors and soil, a rigid-flexible coupling dynamics model of the riser-LMRP/BOPs-wellhead system is established based on the theory of rigid-flexible coupling dynamics and Lagrange equation, which is numerically solved by the Newmark method. To verify the correctness of the proposed model, a simulation model of the riser-LMRP/BOPs-wellhead system is applied, which is modelled by the combination of pipe and mass elements. The research results demonstrate that the numerical results of the proposed theoretical model agree with the simulation results of the coupling system, thus verifying the correctness of the proposed model and revealing the rigid-flexible coupling mechanism between the riser and LMRP/BOPs.

Subsea wellhead system (SWS) is the foundation of oil and gas well construction and the crucial channel of intervene operation. As the safety barrier of well control, the inappropriate management and control of SWS fatigue life would lead to catastrophic safety accidents. This paper puts forward a data-driven LSTM-based fatigue life management and control methodology for SWS, integrating data monitoring, a data-driven LSTM model, probability density function (PDF) and reliability assessment. In detail, monitored parameters are mapped into the load spectrum assisted by a data-driven LSTM model to assess the SWS fatigue damage. Considering fatigue uncertainty, the PDF of fatigue damage is constructed to analyze possible accumulation damage evolution paths of SWS. Further, the relationship among reliability, the accumulated fatigue and the main load amplitude is predicted to determine the health index characterizing the fatigue magnitude and the operation risks of SWS. The analysis results illustrate that the main bending stress amplitude can be deemed as SWS health index, as it can reflect the fatigue status and the reliability of SWS. Thus, the real-time health index provides a vital reference for operators to take timely and effective measures, achieving the management and control of SWS fatigue life.

The traditional check valves mainly include lift check valves and swing check valves, but the lift check valve has a larger fluid resistance, and the swing check valve has a longer opening/closing time and slow dynamic response. In this paper, a new type of flap check valve is proposed based on the inspiration of the heart valve. To study the dynamic response of the valve and the flow characteristics of the flow field in the valve, a three-dimensional analysis model of the valve is established based on the dynamic mesh theory using the computational fluid dynamics (CFD) method, and the CFD simulation of the flow characteristics of the valve is carried out by setting the boundary conditions and working parameters. The transient flow field characteristics and the force state of the valve disc are discussed and analyzed. The simulation results show that: the dynamic response of the flap check valve in the process of opening and closing is faster than that of the swing check valve, and the flow line of the valve is close to laminar flow, so it is not easy to have turbulent flow phenomenon similar to that in the lift check valve.

Vortex-induced vibration (VIV) is a prevalent phenomenon observed in marine submersible buoys subjected to ocean currents, significantly compromising the structural fatigue life and sensor stability. Meanwhile, the provision of in-situ energy supply and long-term sustainability pose significant challenges for marine submersible buoys. To tackle these issues, this paper presents a novel approach that entails the simultaneous utilization of VIV energy and suppression of VIV through the implementation of a rolling-structured, freestanding triboelectriclayer-based nano-generator (RF-TENG). An experimental investigation has been conducted to explore the power generation mechanism of RF-TENG when subjected to VIV excitation, as well as the vibration suppression effect of RF-TENG on VIV. The following conclusions have been drawn: (1) The maximum power generation is observed within the filling rate range of 50%-60%, where the conversion of kinetic energy to electrical energy resulting from particle friction prevails. Correspondingly, the maximum vibration suppression rate is achieved within the filling rate range of 60%-90%, primarily attributed to energy dissipation due to particle collisions. Notably, at approximately 60%-70% filling rate, RF-TENG exhibits a relatively efficient and balanced performance in terms of both energy utilization and vibration suppression. (2) Particle motion irregularity is a prominent factor that greatly influences the power conversion efficiency, which is manifested as the presence of the third harmonic component in the output voltage and current. The power conversion efficiency of RF-TENG attains its peak value at a filling rate of 50%. (3) Within a certain range, an increase in particle diameter contributes to enhancing the robustness and VIV suppression efficiency of RF-TENG. However, it comes at the cost of reduced power generation capacity. In this study, under the excitation of VIV experienced by a cylinder with an effective amplitude of approximately 1.56 cm and a frequency of approximately 1.62 Hz, RF-TENG achieves a power generation density of 80 mW/m3 and a VIV amplitude suppression rate of 24%. These results suggest that RF-TENG is an effective method for synchronously collecting energy and suppressing VIV in marine structures.

The fatigue reliability assessment of deepwater risers plays an important role in the safety of oil and gas development. Physical-based models are widely used in riser fatigue reliability analyses. However, these models present some disadvantages in riser fatigue reliability analyses, such as low computational efficiency and the inability to introduce inspection data. An improved fatigue reliability analysis method was proposed to conduct the fatigue reliability assessment of deepwater risers. The data-driven models were established based on response surface methods to replace the original physical-based models. They are more efficient than the physics-based model, because a large number of complex numerical and iterative solutions are avoided in fatigue reliability analysis. The annual crack growth model of the riser based on fracture mechanics was established by considering the crack inspection data as a factor, and the crack growth dynamic Bayesian network was established to evaluate and update the fatigue reliability of the riser. The performance of the proposed method was demonstrated by applying the method to a case. Results showed that the data-driven models could be used to analyze riser fatigue accurately, and the crack growth model could be performed to analyze riser fatigue reliability efficiently. The crack inspection results update the random parameters distribution and the fatigue reliability of deepwater risers by Bayesian inference. The accuracy and efficiency of fatigue analysis of deepwater risers can be improved using the proposed method.

The classical wake oscillator model is capable of predicting the vortex-induced vibration response of a cylinder at high mass-damping ratios, but it fails to perform satisfactorily at low mass-damping ratios. A modified wake oscillator model is presented in this paper. The modification method involves analyzing the variation law of the add mass coefficient of the cylinder versus reduced velocity and expressing the reference lift coefficient CL0 as a function of the add mass coefficient. The modified wake oscillator model has been demonstrated to have better accuracy in capturing maximum amplitudes and flow velocity at low mass-damping ratios. However, the modified model at present form is unable to accurately predict the vortex-induced vibration response at high damping ratios. The purpose of this paper is to propose a new modification idea. In order to achieve better results when applying this modification idea to particular objects, it may be necessary to first understand the response law of these kinds of objects.

This paper discusses the effects of marine riser connectors (MRCs) on fatigue failure risk using multi-coupling models. When MRCs are subjected to vortex-induced fatigue, a risk early warning strategy is used for effective risk monitoring as a preventive measure for the operation of MRCs. To ensure safe marine oil and gas production and to improve fatigue failure prevention and control, research on offshore structural fatigue risk failure theory criteria and evaluation and the vibration fatigue characteristics of MRCs over time and frequency is characterized. By coupling data-driven technological means, including rain-flow counting (RFC), Hilbert–Huang transform (HHT), power spectral density (PSD), artificial neural network (ANN), risk-based inspection (RBI), and risk management measures (RMM) to assess the fatigue risk characteristics of in-service members in special offshore environments. The fluid-structure interaction characteristics of MRCs and a load spectrum are analysed by empirical mode decomposition (EMD) to determine the changes in the components of an intrinsic mode function (IMF) and investigate the degree of fatigue damage. The fatigue damage of MRCs is predicted using the PSD of the IMF and the RFC of the IMF-coupled ANN time series prediction model. The results show that using any IMF component or combined component data as input to the ANN and training set facilitates cross-validation of the analysis. When the input layer and a hidden layer of the ANN are optimized and properly trained, the predicted performance is suitable. Through early warnings and coordination, the spread of fatigue failure risk trends can be predicted, and warning information is issued accordingly.

深水高温高压气井钻井过程中,井筒大温差、大压差效应会使钻井液性能发生较大改变,进而影响井筒流动参数和钻井施工安全,因此准确模拟井筒温压场对确保深水高温高压井安全钻进至关重要.根据深水钻井工艺和高温高压地层的特点,充分考虑了井筒温压场和钻井液性能相互影响,结合增压管线流体进入隔水管环空引起的传热和传质,建立了适用于深水高温高压气井钻井的井筒瞬态温度压力耦合计算模型,提出了相应的迭代求解算法,并通过实例计算,进行了参数敏感性分析.研究结果表明:本文模型计算值与现场实测数据基本吻合,验证了模型的正确性;隔水管增压管线排量会使环空温度显著降低,进而影响整个井筒温度,因此不可忽略增压排量的影响;钻井液性能受井筒温度和压力影响较明显,在计算过程中忽略温度,压力和钻井液性能之间的耦合作用会产生较大误差.本文研究成果可为深水高温高压气井钻井过程中井筒温压场预测及水力参数设计提供理论指导.

Low-cost midsize workover operation based on deepwater workover riser system is attractive. However, a comprehensive theoretical mechanical model for the complex workover riser system has not been found in present studies. In this paper, a coupled mechanical model of the workover riser system is established based on Euler-Bernoulli beam theory, hydraulic-pneumatic principles and the coupling relationship among workover risers, split tensioner system and workover platform. An analysis method for the coupled mechanical model is proposed based on the finite element method, Newmark-β method and Newton-Raphson method. A mechanical analysis program is finally developed in MATLAB and applied in mechanical property analysis of a deepwater workover riser system. It turns out that the bending moment of the workover riser system near the top part, tension ring and bottom part reaches extremes. Dynamic response envelopes of the workover riser system are obviously larger than static responses due to the dynamic excitation of wave loads and platform motions. It is also found that tension distribution ratio has obvious influence on mechanical properties of workover riser system. Mechanical response of the workover riser system decreases with TDR, whether in static or dynamic analyses.

Multibranched horizontal well is an important means to develop low permeability reservoirs. Fishbone multibranched horizontal well has the advantages of increasing drainage area, reducing drilling number, utilizing existing wells, and saving oilfield development cost, especially for marginal oilfield exploitation. The morphological structure of fishbone multibranched horizontal well is very complex, so the numerical simulation study is of great significance to guide the production of fishbone multibranched horizontal well. In this paper, the numerical model is established for fishbone multibranched horizontal well in the oil reservoir. The finite element method is used to numerically solve the mathematic model. The oil well production can be achieved by using the material balance method. Sensitivity analysis is made on the important reservoir and well-type factors that affect the production behavior and transient pressure distribution of fishbone multibranched horizontal well. It is concluded that the effective reservoir thickness and flowing bottomhole pressure have great influence on the productivity, but the influence of heterogeneity is not obvious. The length of main wellbore has great effect on the productivity in the early stage. Fishbone multibranched horizontal wells should be placed in the middle of the reservoir to increase productivity. Branch length, branch angle, branch number, and branch spacing are important parameters affecting the productivity of fishbone multibranched horizontal well. The variation of these parameters has obvious influence on the stimulation effect in the early stage of production, but the influence degree is different. Under the premise of drilling technology and drilling safety, the comprehensive impact of these four factors on productivity should be considered simultaneously. The presented model and obtained results not only enrich production behavior analysis of fishbone multibranched horizontal well but also have significance on formulation of stimulation measures and efficient low permeability reservoir development.

由于初始过盈量和介质压力的作用,井下流量控制阀径向金属密封唇部的应力和应变梯度变化很大,很容易发生塑性变形.为研究径向金属密封唇部接触力学行为,提出径向金属密封唇部的圆弧结构,基于接触力学建立径向金属密封唇部轴对称结构的圆弧-平面接触模型,得出径向金属密封唇部结构接触力学参数的理论关系式,并基于有限元方法进行验证.径向金属密封唇部接触力学参数的理论解与数值解相符,接触宽度、最大接触应力、初始过盈量和平均接触应力的平均相对误差分别为8.86％、6.96％、8.88％和4.33％,满足工程设计要求.研究表明:径向金属密封唇部的最大接触应力与初始过盈量、径向金属密封唇部径向厚度和轴向厚度成正比,与径向金属密封唇部圆弧半径成反比,因此可通过增加初始过盈量、径向金属密封唇部径向厚度和轴向厚度来增加径向金属密封唇部的最大接触应力.研究结果为井下流量控制阀径向金属密封的设计提供了理论指导.