Search Results (146)

Offshore drilling operations face the critical challenge of maintaining precise weight-on-bit (WOB) control during automatic drilling feed while subjected to vessel heave disturbances. This study investigates an integrated closed-circuit hydraulic cylinder lifting system that combines full-stroke drill string compensation with potential energy recovery capabilities, addressing the control coupling problem inherent in traditional split-design systems. A longitudinal vibration model of the drill string is established using lumped mass, stiffness, and damping principles incorporating the Rayleigh method. A co-simulation model implementing nested PID control logic is developed on the AMESim platform to evaluate automatic drilling feed performance under both passive and semi-active compensation modes. Simulation results demonstrate that the proposed integrated control strategy effectively mitigates bottom-hole WOB fluctuations, with top drive velocity accurately tracking set drilling feed rates (0.01–0.02 m/s) within a response time of approximately 10 s. The system maintains operational stability under sea conditions up to Grade 6 (heave wave height ≤ 4.578 m, period 14 s), beyond which accumulator piston limit-stroke collision risks emerge. These findings validate the feasibility of integrated hoisting-compensation design and establish quantitative operational limits, providing theoretical foundations for next-generation marine drilling systems targeting ultra-deepwater and natural gas hydrate exploitation. Full article

The Quemocuo area in the Qiangtang Basin is a key prospect for permafrost gas hydrate exploration in China. This study investigates source-reservoir-caprock characteristics and their control on gas hydrate accumulation based on drilling results from wells QK-8 and QK-9, integrated with multiple analytical methods. Two high-quality marine source rocks with cumulative thickness ~1000 m exhibit TOC values of 0.74–2.5%, Type II₂ kerogen, and vitrinite reflectance (Ro) of 1.37–2.94%, indicating high to over-mature thermal evolution primarily generating dry thermogenic methane. Gas logging shows hydrocarbon anomalies with a maximum desorbed gas content of 90 mL, confirming strong gas generation capacity. Although reservoir matrix properties are poor (porosity mostly <5%, permeability < 0.2 × 10⁻³ μm²), multi-phase tectonics and dissolution formed a secondary fracture-vug system. Permafrost conditions are favorable (thickness 100–120 m; geothermal gradient 4.5–4.7 °C/100 m), with extremely low permeability at high ice saturations, forming an effective multi-level seal together with thick mudstones. A key novel finding is the significant mixing of biogenic and thermogenic gases, with the biogenic component interpreted to originate from overlying Jurassic-Quaternary low-maturity strata, facilitated by late tectonic uplift and fault conduits. NW-trending faults connect deep thermogenic reservoirs and provide pathways for shallow biogenic gas migration. For the first time, this study establishes a region-specific composite accumulation model for the Qiangtang Basin, characterized by “lower generation and upper storage, fault-fracture conduit and permafrost sealing”, which reveals fault-controlled migration, fracture-vug-controlled storage, permafrost-controlled sealing, and mixed gas enrichment under a high geothermal gradient. Full article

Natural gas hydrate is a clean energy resource critical for global energy security and low-carbon transition. Understanding its geological accumulation mechanisms is essential for exploration and development. However, the current research on NGH geological accumulation lacks a systematic and quantitative analysis of its global research evolution, hotspots, and frontiers. To fill this gap, this study conducts a bibliometric analysis of 5891 articles (1999–2025) from the Web of Science Core Collection using CiteSpace and VOSviewer to map research trends, contributions, and frontiers. The results show that annual publications followed a three-stage trajectory: slow initiation, rapid growth, and stable development, with key boosts from production tests in Japan (2013) and China (2017). Marine and Petroleum Geology emerged as the most cited journal. China, the United States, and Germany lead research output, with the Chinese Academy of Sciences serving as the central hub (centrality: 0.46). Core researchers such as Jinqiang Liang have established foundational knowledge through highly cited studies on accumulation theory and resource–environment interactions. Research focus has shifted from early resource assessment to controlling factors, and recently toward production technologies and parameter optimization, highlighting a transition from basic to applied research with strong interdisciplinary integration. While bibliometrics reveals structural evolution and hotspots, limitations in data sources and analytical scope remain. Future efforts should integrate multi-source data and deepen content analysis to address unresolved challenges in NGH geological accumulation. Full article

Natural gas hydrates, as an abundant potential energy resource, are widely present in marine sediments. In this paper, a novel method using color recognition technology is proposed for reconstructing marine hydrate reservoirs. By identifying the red, green, and blue values of image colors within the study area’s grid, numerical values are assigned and translated into geological parameters. These parameters are then input into the Computer Modeling Group software to establish heterogeneous reservoirs, and numerical simulations are conducted. The results indicate that this method successfully establishes a correspondence between color features and geological parameters. The reconstructed model images exhibit a high degree of consistency with the original images, allowing for precise parameter readings. The method was applied to hydrate reservoirs in the second trial production area of the South China Sea, the Shenhu SH2 area, and the Nankai Trough. The cumulative gas production obtained through numerical simulation of the reconstructed models closely matched the known production data, with discrepancies of 3.5%, 0.9%, and 7.6%, respectively. These findings confirm the reliability of the model, providing valuable insights for future studies on heterogeneous hydrate reservoirs and extending its application prospects to heterogeneous oil and gas reservoir research. Full article

Dynamic phase transition of natural gas hydrates confined within complex pore–throat structures is a key factor impacting the safe and efficient development of hydrate-bearing deposits. In this work, hydrate-bearing samples with varying saturation were first reconstructed with the proposed ice-seeding method using actual marine soil in hydrate-bearing sediments from the South China Sea. Dynamic evolution characteristics of hydrate formation in evolving porous media under different temperature and pressure conditions were analyzed in detail. Combined with high-resolution CT scanning, image processing, pore network extraction, and statistical analysis, the typical microscopic pore–throat structures of hydrate-bearing sediments were revealed, and the presence of nanopores was identified. Furthermore, highly controllable heterogeneous pore–throat structures were constructed for microfluidic chips by integrating stochastic modeling, equivalent modeling, and machine learning approaches. On this basis, a novel microfluidic testing method was developed for investigating the dynamic formation, dissociation, and phase transition characteristics of natural gas hydrates in complex pore structures by controlling the temperature. This study provides reliable data support and theoretical guidance for the productivity prediction of marine hydrate-bearing deposits. Full article

Investigations into the production of gas hydrates from marine sediments have demonstrated that commercial viability necessitates a daily gas production rate of 130,000 to 200,000 m³. However, the second-round trial production in the South China Sea yielded only 28,700 m³/day, falling short of the rule-of-thumb for economic feasibility. Given the coexistence of natural gas hydrates (NGHs) and shallow gas in the subsurface reservoirs of the South China Sea, a co-production strategy (simultaneously exploiting NGHs and shallow gas) was proposed to reduce costs and enhance production efficiency. In this study, a large-scale, three-dimensional, multi-phase, and multi-component model was established based on the NGHs–shallow gas symbiotic system in the Qiongdongnan Basin. A dual horizontal well configuration was designed to extract NGHs from the hydrate-bearing layer and natural gas from the underlying shallow gas layer. Co-production via dual horizontal wells expanded the hydrate dissociation zone from the near-wellbore region to deeper strata, particularly enhanced the dissociation of NGHs in the region between the two horizontal wells. By the 10th year of simulation, the peak and cumulative volume rate of CH₄ released from hydrate dissociation increased to 3.52 and 1.45 times under the co-production scenario, resulting in a 2.4-fold improvement in NGH recovery efficiency. Sensitivity analyses of bottom hole pressure and length of the horizontal intervals revealed that reducing bottom hole pressure significantly improved the daily and accumulative gas production from hydrate-bearing reservoirs. The length of horizontal intervals emerged as a critical factor influencing the dissociation of NGHs, whereas it had negligible impact on gas production from shallow gas reservoir with satisfied permeability. This study provides insights into optimizing the development of marine hydrate resources via integrated exploitation strategies. Full article

Polymer additives in well cement slurry filtrate would affect the stability of natural gas hydrate (NGH), which could lead to formation collapse and cause marine disasters. It is necessary to clarify the critical conditions for the stability of NGH, i.e., NGH phase equilibrium. LAMMPS software and the TIP4P model were used to develop a method for calculating NGH phase equilibrium. Based on the single functional groups and combined functional groups of polymer additives, the potential energy, angular order parameter (AOP) of water molecules, and NGH phase equilibrium temperatures under different pressures were calculated, and a phase equilibrium curve was characterized. Results show that amide groups promote NGH decomposition more strongly than carboxyl and sulfonate groups, with a 1.5% dodecylamide system causing NGH phase equilibrium temperature to decrease by 1.68–2.77 K. AM/AA promotes NGH decomposition more strongly than AA/AMPSNa, AM/AMPSNa, and AA/AMPSNa/AM, with a 1.5% AM/AA system causing NGH phase equilibrium temperature to decrease by 2.33–3.56 K. To ensure the safety of well cementing and marine environments, the contents of amide groups and carboxyl groups should be reduced when developing polymer additives for cement slurry used in NGH formation cementing. Full article

Efficient development of marine natural gas hydrates (NGHs) remains challenging. Employing depressurization combined with complex structured wells and reservoir stimulation techniques is one of the key approaches to enhancing production. This study aims to theoretically evaluate the production response of different lateral layouts of multilateral wells under the conceptual condition of an idealized boundary sealing for the depressurization exploitation of Class 1 hydrate reservoirs. Based on data from China’s first offshore trial production, a numerical simulation method was used to systematically compare the development performance of various lateral layouts integrated with boundary sealing. Under the idealized modeling scenario, the simulation results indicate that the low-permeability barrier formed by boundary sealing can significantly suppress water invasion, promote pressure propagation, and thereby improve productivity. More importantly, optimizing the lateral layout can further enhance gas production performance. Under boundary sealing conditions, Case 8B with six downward-deployed laterals, compared to Case 1A without sealing and with six laterals in a planar staggered layout, its cumulative gas production (1733.75 × 10⁴ m³) was 2.08 times that of Case 1A (831.68 × 10⁴ m³), and its gas-to-water ratio (327.64) was 1.62 times that of Case 1A (202.09). This indicates that under boundary sealing conditions, lateral layout is one of the key levers to improve productivity. Under the modeling assumptions of this work, the research findings can provide a theoretical reference for evaluating the development of Class 1 hydrate reservoirs with multilateral wells where boundary sealing is considered. Full article

Safe exploitation of the marine natural gas hydrate (NGH) resource is essential to meet the demand of the future energy requirement. To enable real-time monitoring of methane leakage during the production test of NGH, an ocean stereoscopic monitoring system based on underwater single-point mooring structure is developed, which supports in situ monitoring of marine environment at the sea-air interface, the euphotic zone, and the seabed boundary layer. Numerical simulations were conducted to evaluate the effect of mooring configuration, cable lengths, and buoyancy settings on the mooring stability of the system against the current and waves. Based on the simulation result, an optimized segmented inverse-catenary mooring configuration is developed to achieve a balance between the performance and cost. The designed submersible relay buoy isolates the upper dynamic S-shaped cable from the lower static straight electro-optical-mechanical (EOM) cable, thereby improving system stability. The monitoring system based on the optimized mooring structure is successfully deployed at the NGH zone in the northern South China Sea at the water depth of 1330 m confirming its working stability in harsh sea conditions. Full article

Evaluation of gas hydrate stability in marine sediments is commonly conducted assuming pure methane systems, although increasing drilling and logging evidence indicates that natural gas hydrates frequently contain minor amounts of heavier hydrocarbons. In the northern South China Sea, the presence of ethane has been widely reported, yet its influence on hydrate phase equilibrium and the distribution of the gas hydrate stability zone (GHSZ) remains insufficiently quantified. The results show that ethane is preferentially incorporated into large cages and promotes structure II hydrate stability, leading to lower dissociation pressures and higher stability temperatures compared with pure methane hydrates. Incorporation of as little as 1 mol% ethane systematically deepens the predicted base of the GHSZ and enlarges the hydrate-free gas coexistence interval beneath the bottom-simulating reflector (BSR). These effects indicate that conventional pure CH₄ models underestimate both the thickness of the hydrate stability zone and the potential extent of hydrate occurrence. At the regional scale, composition-dependent stability provides a coherent explanation for discrepancies between seismic BSR depths and hydrate predictions. This study establishes a composition-sensitive framework for regional GHSZ evaluation, demonstrating that even trace hydrocarbons must be considered to reliably assess hydrate occurrence, resource potential, and associated geohazards in continental margin settings. Full article

Suction anchors play an important role in the exploration and development of marine natural gas hydrate (NGH). Suction anchors increase the bearing capacity and reduce tilting or sinking risk of underwater wellheads in the exploration and development process. This study proposes a dynamic failure analysis procedure for suction anchor installation based on the DBN-GO method. Firstly, a Goal-Oriented (GO) model is established by analyzing the human and equipment factor nodes in the suction anchor installation operation process. A Bayesian Network (BN) analysis model is set up by mapping the key nodes in the GO model. Then, the Cognitive Reliability and Error Analysis Method (CREAM) and the Dempster–Shafer (D-S) evidence theory are used to quantify the failure probabilities of human and equipment factor nodes in the BN model. The main risk factors are identified using Bayesian backward inference. Finally, the dynamic risk assessment of the suction anchor installation operation is conducted, considering the equipment node transition probability of the BN. Tkae the second production test of natural gas hydrates in the South China Sea as a case study. The study result shows that the failure probability of the suction anchor installation operation is 0.298%, which is at a low-risk level. Suction pump pressure control is the most critical factor leading to human errors. Among the equipment factor, the reliability of the suction pump and the ROV is the most important. Dynamic Bayesian inference shows the risk gradually increases with time. A reasonable maintenance strategy is conducive to reducing the accumulated risks caused by the time-varying degradation of equipment performance. The results could provide significant support in risk management and decision-making for the suction anchor installation operation, which will further promote the environmental sustainability, operational safety and economic feasibility of marine natural gas hydrate development. Full article

The homogeneity of methane hydrates in marine sediments plays a significant role in determining the efficiency of gas production during exploitation processes. Revealing their distribution mechanisms is crucial for optimizing the development of gas hydrates. This work systematically investigates the evolution patterns of effective thermal conductivity (ETC) during the formation and dissociation of methane hydrate in marine sediments, focusing on their major mineral components, such as quartz sand, illite, and montmorillonite. The results reveal the influence of thermal conductivity (TC) characteristics in porous media on hydrate phase transition behavior and spatial distribution. Key findings demonstrate that the TC characteristics of porous media are one of the dominant factors controlling hydrate formation rates. High-conductivity porous media significantly accelerate hydrate formation through efficient heat transfer. The swelling characteristics of montmorillonite and its coupling effects with salt ions impair heat transfer pathways, thereby inhibiting hydrate formation. Further analysis reveals that the spatial heterogeneity in reservoir TC is the primary intrinsic mechanism responsible for the macroscopic heterogeneous distribution of hydrates. Additionally, the hydrate dissociation process disrupts solid-state thermal bridging and generates gaseous thermal barriers, causing irreversible attenuation of reservoir TC. This phenomenon exacerbates the non-uniformity of the front during dissociation and increases the risk of secondary formation during exploitation. From a novel perspective of reservoir TC heterogeneity, this study establishes mechanistic links between the thermophysical properties of porous media and the spatial distribution patterns of hydrates. This provides significant theoretical guidance for resource exploration and the safe, efficient exploitation of marine gas hydrate reservoirs. Full article

The electrical resistivity and acoustic properties of marine sediments are essential for understanding their physical and mechanical behavior. Over recent decades, significant advancements have been made in both in situ and laboratory measurement techniques, alongside theoretical models, to establish correlations between these geophysical parameters and sediment properties such as porosity, saturation, and consolidation degree. However, a comprehensive comparison of the advantages, limitations, and applicability of different measurement methods remains underexplored, particularly in complex scenarios such as gas hydrate-bearing sediments. This review provides an in-depth synthesis of recent developments in in situ and laboratory testing technologies for assessing the resistivity and acoustic characteristics of marine sediments. Special emphasis is placed on the latest advances in acoustic measurements during gas hydrate formation and decomposition. The review highlights key challenges, including (1) limited vertical resolution in in situ resistivity measurements due to probe geometry; (2) errors arising from electrode polarization and poor soil–electrode contact; and (3) discrepancies in theoretical models linking geophysical parameters to sediment properties. To address these challenges, future research directions are proposed, focusing on optimizing electrode array designs for high-resolution resistivity measurements and developing non-destructive acoustic techniques for deep-sea sediments. This work offers a critical reference for marine geophysics and offshore engineering researchers, aiding the selection and development of testing technologies for effective marine sediment characterization. Full article