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Copyright of Low-Carbon Chemistry & Chemical Engineering is the property of Low-Carbon Chemistry & Chemical Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This research deals with gas hydrates formation and dissociation within a marine quartz-based porous sediment and in batch conditions. Hydrates were formed with small-chain hydrocarbons included in natural gas mixtures: methane and also ethane and propane. The dissociation values were collected and provided both graphically and numerically. The results were then compared with the theoretical hydrate-liquid-vapor phase boundary equilibrium for the same species, defined according to the existing literature. The deviation of the experimental results from the ideal ones, associated with the porous sediment, was quantified and discussed. For the scope, the grain size distribution and chemical composition of the sediment were provided along with the text. The results proved that the different size of guest species and, consequently, the different hydrate structures formed, played a relevant role in determining the promoting, inhibiting or neutral behavior of the porous sediment during the process. [ABSTRACT FROM AUTHOR]

This study reports an investigation into both isotropic and anisotropic permeability effects on gas production behavior during depressurization-induced natural gas hydrate dissociation at site NGHP-01-10D in the Krishna-Godavari basin. Numerical simulations were performed on a reservoir-scale model incorporating a single vertical well, examining different scenarios of permeability ratios (rrz). The investigation assessed gas and water production rates, cumulative production volumes, the gas-to-water ratio, and the spatial distribution of reservoir parameters throughout a production duration of 3 years. The findings indicate that permeability anisotropy has a substantial impact on hydrate dissociation and gas recovery. For rrz > 1, horizontal pressure propagation was promoted and gas production increased. For example, at t = 1100 days, the total gas production improved from 7.88 × 105 ST m3 for rrz = 1 to 55.9 × 105 ST m3 for rrz = 10. For rrz < 1, vertical pressure propagation resulted in higher water production with concomitantly lower rates of gas production rates. Spatial distribution analysis revealed that higher rrz values led to more extensive radial propagation of pressure drop, temperature decrease, gas saturation increase, and hydrate dissociation. The study concludes that higher horizontal permeability enhances depressurization effects, resulting in higher gas production rates and more favorable gas-to-water ratios. [ABSTRACT FROM AUTHOR]

During drilling operations, drilling fluids undergo heat exchange with hydrate-bearing formations. The intrusion of drilling fluids affects hydrate stability, leading to variations in stress fields around a wellbore and complex scenarios such as borehole collapse, significantly hindering the efficient development of natural gas hydrate resources. This study establishes a thermo-hydro-mech model for hydrate-bearing inclined wells based on linear thermoelastic porous media theory and an appropriately high inhibitive drilling fluid temperature. This research reveals that drilling should follow directions of minimum horizontal stress or perpendicular to maximum horizontal stress during drilling operations to control wellbore stability. Hydrate decomposition due to factors like drilling fluid pressure and temperature can rapidly reduce the strength of low-saturation formations, significantly increasing the risk of wellbore instability. Therefore, selecting appropriate highly inhibitive and low-temperature drilling fluids during drilling operations helps control hydrate decomposition and reduce fluid intrusion, thereby mitigating risks associated with wellbore instability. [ABSTRACT FROM AUTHOR]

A differential thermal analysis study was carried out on the formation and decomposition of hydrates in systems containing natural gas, sand, and 5 mass % aqueous NaHCO3 as well as natural gas, sand, and 5 mass % aqueous NaCl with initial gas pressures from 3 to 9 MPa. Equilibrium conditions, enthalpy of dissociation, and the kinetic parameters of hydrate formation were determined. Hydrate formation in the system containing aqueous sodium bicarbonate proceeds at higher temperatures and lower pressures and has higher kinetic parameters than in the system with aqueous sodium chloride of the same concentration. Composition of the solutions is one of the factors affecting hydrate formation in the studied systems. The HCO3– ion is found to have a greater structure-making effect than the Cl– ion, which leads to differences in the thermodynamic conditions and kinetic parameters of natural gas hydrate formation in a porous medium. [ABSTRACT FROM AUTHOR]

During the operational process of natural gas gathering and transmission pipelines, the formation of hydrates is highly probable, leading to uncontrolled movement and aggregation of hydrates. The continuous migration and accumulation of hydrates further contribute to the obstruction of natural gas pipelines, resulting in production reduction, shutdowns, and pressure build-ups. Consequently, a cascade of risks is prone to occur. To address this issue, this study focuses on the operational process of natural gas gathering and transmission pipelines, where a comprehensive framework is established. This framework includes theoretical models for pipeline temperature distribution, pipeline pressure distribution, multiphase flow within the pipeline, hydrate blockage, and numerical solution methods. By analyzing the influence of inlet temperature, inlet pressure, and terminal pressure on hydrate formation within the pipeline, the sensitivity patterns of hydrate blockage risks are derived. The research indicates that reducing inlet pressure and terminal pressure could lead to a decreased maximum hydrate formation rate, potentially mitigating pipeline blockage during natural gas transportation. Furthermore, an increase in inlet temperature and terminal pressure, and a decrease in inlet pressure, results in a displacement of the most probable location for hydrate blockage towards the terminal station. However, it is crucial to note that operating under low-pressure conditions significantly elevates energy consumption within the gathering system, contradicting the operational goal of energy efficiency and reduction of energy consumption. Consequently, for high-pressure gathering pipelines, measures such as raising the inlet temperature or employing inhibitors, electrical heat tracing, and thermal insulation should be adopted to prevent hydrate formation during natural gas transportation. Moreover, considering abnormal conditions such as gas well production and pipeline network shutdowns, which could potentially trigger hydrate formation, the installation of methanol injection connectors remains necessary to ensure production safety. [ABSTRACT FROM AUTHOR]

Submarine hydrate mining can trigger geological disasters, including submarine landslides and seafloor subsidence due to excess pore pressure and weakened layers, which may potentially lead to the reactivation of faults and increased seismic activity. However, current research encounters challenges in assessing geotechnical issues associated with long-term and large-scale production from well grids located in sloped areas. Limited by the complexity of the hydrate sediment, a multifield coupled numerical model of hydrate slope in the Shenhu area was established. Utilizing the modified Mohr–Coulomb model as the constitutive model for hydrate-bearing sediments to track the dynamic reduction in strength and employing the shear strength method to assess submarine slope stability, a series of depressurization strategies are applied to evaluate the risks associated with submarine landslides and seafloor subsidence. Results show that the hydrate dissociation tends to stagnate after a period of mining. The strength of the hydrate decomposed area is severely reduced, and a volume deficit occurs in this area, causing formation displacement. The peripheral region of the decomposed area is compacted by high stress, resulting in a serious decrease in permeability and porosity, which limits the continued decomposition of hydrates. The large-scale submarine landslides with hydrates decomposition will not appear in this block. However, several meters' seafloor subsidence over a wide range risks engineering safety significantly. The amount of seafloor subsidence in the first 50 days is approximately half of the final settlement. A higher production pressure drop can speed up the recovery rate while resulting in more significant seafloor subsidence and slippage. Therefore, the balance between mining speed and formation stability needs more research work. [ABSTRACT FROM AUTHOR]

As the understanding of natural gas hydrates as a vast potential resource deepens, their importance as a future clean energy source becomes increasingly evident. However, natural gas hydrates trend towards secondary generation during extraction and transportation, leading to safety issues such as pipeline blockages. Consequently, developing new and efficient natural gas hydrate inhibitors has become a focal point in hydrate research. Kinetic hydrate inhibitors (KHIs) offer an effective solution by disrupting the nucleation and growth processes of hydrates without altering their thermodynamic equilibrium conditions. This paper systematically reviews the latest research progress and development trends in KHIs for natural gas hydrates, covering their development history, classification, and inhibition mechanisms. It particularly focuses on the chemical properties, inhibition effects, and mechanisms of polymer inhibitors such as polyvinylpyrrolidone (PVP) and polyvinylcaprolactam (PVCap). Studies indicate that these polymer inhibitors provide an economical and efficient solution due to their low dosage and environmental friendliness. Additionally, this paper explores the environmental impact and biodegradability of these inhibitors, offering guidance for future research, including the development, optimization, and environmental assessment of new inhibitors. Through a comprehensive analysis of existing research, this work aims to provide a theoretical foundation and technical reference for the commercial development of natural gas hydrates, promoting their safe and efficient use as a clean energy resource. [ABSTRACT FROM AUTHOR]

Accurate control of natural gas flow and pressure is essential to achieving multi-gas combined production of the natural gas hydrates. In this study, a downhole stratification control tool for controlling natural gas flow rate and pressure with a multi-stage throttling structure was innovatively proposed. The multi-stage throttling structure combined an adjustable cage sleeve and a fixed nozzle. The numerical model of the internal flow field of the downhole stratification control tool was established. Through the computer fluid dynamics numerical simulation, the flow field change law inside the spool module of the downhole stratification control tool under different spool structures, different outlet pressures, and different spool openings was analyzed. Moreover, the spool module prototype was processed, and the indoor experiment of the spool's performance of reducing pressure and regulating production was carried out. The results show that the multi-stage throttling structure has the advantages of adjustable spool opening and moderate cooling range and the mass flow of gas inside the spool changes linearly with the opening of the spool. The spool module can accurately control the mass flow of natural gas under high-pressure conditions, and meet the needs of the downhole stratification control tool for accurate gas control. • A DSCT with multi-stage throttling structure is proposed. • The throttling structure composed of a cage sleeve and a fixed nozzle. • The flow field of multi-stage throttling structure is analyzed. • The DSCT can precisely control the gas mass flow under high-pressure conditions. • The pressure drop performance of the multi-stage throttling structure is the best. [ABSTRACT FROM AUTHOR]

Natural gas hydrate has attracted worldwide attention for its abundant availability and clean and nonpolluting combustion products. The actual environment of marine methane hydrates is water‐saturated, but present researches on water‐saturated hydrates are relatively few. This study prepares water‐saturated hydrate sediment of ≈70% saturation and mainly focuses on the thermodynamic and kinetic characteristics of decomposition process using different depressurization rates. Compared with gas‐saturated hydrates, both the thermodynamic evolution and the decomposition kinetics of water‐saturated hydrates get weakened due to the inhibition of water molecules surrounding hydrate crystals on heat and mass transfer. In all experimental cases of water‐saturated hydrates, the temperature still decreases at most 0.5 °C in several minutes after the pressure has become constant, indicating the delay effect of depressurization in water phase. The results show that the increase in depressurization rate strengthens both temperature decrease and pressure delay of water‐saturated hydrate‐bearing sediment. In addition, the decomposition rate of water‐saturated hydrates in depressurization stage is constant and positive to the depressurization rate, while the decomposition rate in constant pressure stage is a function of residual hydrate amount. This study is significant for decomposition control of hydrate mining under actual marine environment. [ABSTRACT FROM AUTHOR]

Submarine hydrate mining can trigger geological disasters, including submarine landslides and seafloor subsidence due to excess pore pressure and weakened layers, which may potentially lead to the reactivation of faults and increased seismic activity. However, current research encounters challenges in assessing geotechnical issues associated with long-term and large-scale production from well grids located in sloped areas. Limited by the complexity of the hydrate sediment, a multifield coupled numerical model of hydrate slope in the Shenhu area was established. Utilizing the modified Mohr–Coulomb model as the constitutive model for hydrate-bearing sediments to track the dynamic reduction in strength and employing the shear strength method to assess submarine slope stability, a series of depressurization strategies are applied to evaluate the risks associated with submarine landslides and seafloor subsidence. Results show that the hydrate dissociation tends to stagnate after a period of mining. The strength of the hydrate decomposed area is severely reduced, and a volume deficit occurs in this area, causing formation displacement. The peripheral region of the decomposed area is compacted by high stress, resulting in a serious decrease in permeability and porosity, which limits the continued decomposition of hydrates. The large-scale submarine landslides with hydrates decomposition will not appear in this block. However, several meters’ seafloor subsidence over a wide range risks engineering safety significantly. The amount of seafloor subsidence in the first 50 days is approximately half of the final settlement. A higher production pressure drop can speed up the recovery rate while resulting in more significant seafloor subsidence and slippage. Therefore, the balance between mining speed and formation stability needs more research work.

This research explores the geomechanical challenges associated with gas hydrate extraction in submarine slope zones, a setting posing a high risk of significant geological calamities. We investigate slope and wellbore deformations driven by hydrate decomposition within a subsea environment. Utilizing Abaqus, a fluid-solid-thermal multi-field coupling model for gas hydrate reservoirs was created. Hydrate decomposition during drilling is minimal, resulting in minor formation deformation near the wellbore. However, a year of hydrate production caused a maximum displacement of up to 7 m in the wellbore and formation, highlighting the risk of submarine landslides. This indicates the need for meticulous surveillance of formation subsidence and wellhead equipment displacement. In the aftermath of a hydrate-induced submarine landslide, both the hydrate layer and the overlying strata descend together, inflicting considerable damage on the formation and wellbore. Our study presents a holistic examination of the interplay between environmental geomechanics risks and engineering structure risks for submarine slope instability and wellbore stability during hydrate development, providing crucial insights for enhancing safety measures in hydrate drilling and production, and ensuring wellbore stability. [ABSTRACT FROM AUTHOR]

As ice-like crystals and non-stoichiometric compounds comprising gas and water, natural gas hydrates have drawn significant attention as a potential alternative energy source. This work focuses on holistically reviewing theoretical modeling and numerical studies conducted on the production of gas from natural gas hydrates. Firstly, fundamental models for the dissociation of a hydrate in a porous sediment are summarized in terms of the phase equilibrium and dissociation kinetics. The main features of different models and improvements for them are identified by clarifying crucial driving mechanisms and kinetic parameters. Subsequently, various numerical works addressing the dissociation of a hydrate in a porous sediment and the flow characteristics in a wellbore are reviewed, including aspects such as the theoretical background, computational scheme, and the physics involved. In general, profiting from a significant capacity to solve nonlinear differential equations, numerical simulations have contributed to great progress in fundamentally understanding the mechanism driving gas production and in developing effective exploitation methods. Owing to the substantial fundamental physics involved in the exploitation of natural gas hydrates, existing challenges, alternative strategies, and future directions are provided correspondingly from a practical application perspective. [ABSTRACT FROM AUTHOR]

The Muli permafrost area is the only midlatitude permafrost area where natural gas hydrates (NGHs) have been drilled. Although a series of achievements has been made in studies on NGH accumulation conditions in the permafrost area, related studies on gas hydrate stability zones, gas sources and groundwater are still controversial and need further work. Based on geophysical, geological and geochemical data, this paper systematically elaborates the main NGH accumulation conditions in the Muli area in terms of the pressure‒temperature stability conditions, fault structure, gas composition, gas source, reservoir characteristics, groundwater distribution and topographic characteristics. The results show that the thicknesses of the NGH stability zone range from 491.0 to 962.7 m. The fault structure can provide a pathway for hydrocarbon gas migration from deep to NGH stability zones, in which thrust faults can prevent the upwards migration of gas by sealing it below the hanging wall block. Rock fractures in the NGH stability zone can not only be gas migration channels, but also serve as a reservoir space for NGH accumulation. The hydrocarbon gas of NGHs shows multiple origins and is mainly composed of oil-associated gas. The formation of frost mounds related to the overpressured gas ejection caused by NGH decomposition may imply the existence of NGHs. Synthetically, similarities and differences in NGH accumulation conditions between the Muli permafrost area and other high-latitude permafrost areas are proposed, and the 'regression' NGH accumulation pattern in the Muli area is constructed. The study results can enrich theoretical knowledge of terrestrial NGH accumulation, and provide scientific guidance for NGH exploration in midlatitude permafrost areas. [ABSTRACT FROM AUTHOR]

Geologic reservoirs containing gas hydrate occur beneath permafrost environments and within marine continental slope sediments, representing a potentially vast natural gas source. Numerical simulators provide scientists and engineers with tools for understanding how production efficiency depends on the numerous, interdependent (coupled) processes associated with potential production strategies for these gas hydrate reservoirs. Confidence in the modeling and forecasting abilities of these gas hydrate reservoir simulators (GHRSs) grows with successful comparisons against laboratory and field test results, but such results are rare, particularly in natural settings. The hydrate community recognized another approach to building confidence in the GHRS: comparing simulation results between independently developed and executed computer codes on structured problems specifically tailored to the interdependent processes relevant for gas hydrate-bearing systems. The United States Department of Energy, National Energy Technology Laboratory, (DOE/NETL), sponsored the first international gas hydrate code comparison study, IGHCCS1, in the early 2000s. IGHCCS1 focused on coupled thermal and hydrologic processes associated with producing gas hydrates from geologic reservoirs via depressurization and thermal stimulation. Subsequently, GHRSs have advanced to model more complex production technologies and incorporate geomechanical processes into the existing framework of coupled thermal and hydrologic modeling. This paper contributes to the validation of these recent GHRS developments by providing results from a second GHRS code comparison study, IGHCCS2, also sponsored by DOE/NETL. IGHCCS2 includes participants from an international collection of universities, research institutes, industry, national laboratories, and national geologic surveys. Study participants developed a series of five benchmark problems principally involving gas hydrate processes with geomechanical components. The five problems range from simple geometries with analytical solutions to a representation of the world's first offshore production test of methane hydrates, which was conducted with the depressurization method off the coast of Japan. To identify strengths and limitations in the various GHRSs, study participants submitted solutions for the benchmark problems and discussed differing results via teleconferences. The GHRSs evolved over the course of IGHCCS2 as researchers modified their simulators to reflect new insights, lessons learned, and suggested performance enhancements. The five benchmark problems, final sample solutions, and lessons learned that are presented here document the study outcomes and serve as a reference guide for developing and testing gas hydrate reservoir simulators.

This research will look at hydrate inhibition, mainly by mono-ethylene-glycol and how this differently affects other areas, and how recovered again. The aim of this study will highlight the current monoethylene-glycol requirement in deep marine gas plant, the wells that still require mono-ethylene-glycol, and the others that do not, along with the volumes needed for inhibition. This search will also provide information of the future requirement for mono-ethylene-glycol in deep marine gas plant, and what options are available to reduce the quantity of MEG required to be injected safely without any impact on production. As it was injected about 14 cubic meter of mono ethylene glycol into the wells, the potential saving from this optimization by using HYSIS program is 3.65 Million dollar / year. Due to the rapidly decline on most wells and increasing aqueous received, the concentration of MEG in aqueous received from wells was lower than the on spec condition of existing MEG recovery unit. So, different scenarios were proposed starting from minimum concentration of MEG, required to operate MEG recovery unit and ending with the maximum concentration. HYSYS simulation program was used to estimate the saved cost of operating the MEG recovery unit at minimum and maximum concentrations which are 35,377,688 $ / year and 409,188,219 $ / year respectively. [ABSTRACT FROM AUTHOR]

Marine natural gas hydrate (NGH) can mainly be found in argillaceous fine-silt reservoirs, and is characterized by weak consolidation and low permeability. Sand production is likely to occur during the NGH production process, and fine-silt particles can easily plug the sand-control media. In view of this, experiments were conducted to assess the influence of the formation sand on the sand retention media in gravel-packed layers under gas–water mixed flow, and the plugging process was analyzed. The results show that following conclusions. (1) The quartz-sand- and ceramic-particle-packed layers show the same plugging trend, and an identical plugging law. The process can be divided into three stages: the beginning, intensified, and balanced stages of plugging. (2) The liquid discharge is a key factor influencing the plugging of gravel-packed layers during NGH exploitation by depressurization. As the discharge increases, plugging occurs in all quartz-sand packing schemes, while the ceramic-particle packing scheme still yields a high gas-flow rate. Therefore, quartz sand is not recommended as the packing medium during NGH exploitation, and the grain-size range of ceramic particles should be further optimized. (3) Due to the high mud content of NGH reservoirs, a mud cake is likely to form on the surface of the packing media, which intensifies the bridge plugging of the packed layer. These experiment results provide an important reference for the formulation and selection of sand-control schemes. [ABSTRACT FROM AUTHOR]

Copyright of Oil Drilling & Production Technology / Shiyou Zuancai Gongyi is the property of Shiyou Zuancai Gongyi Bianjibu and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper provides a feasibility model of using satellite imaging technology to indicate hydrate presence and evaluate gas hydrate saturation trapped in the premises of Pakistan. The study compiles an effort to justify the potential of gas hydrates in Pakistan and their effective extraction. Satellite images of the Arabian Sea are correlated with previously available Bottom Simulating Reflectors (BSRs) to predict the presence of hydrates and potential energy trapped in them. Additionally, the innovative and optimistic hydrate-detection technique of thermal imaging is merged to add the methodological value. The thermal gradient helps to understand the thermodynamic behavior of subsea natural gas hydrates in particular area. Unfortunately, gas production from hydrates is still commercially unaccepted because very limited ventures have been launched in this domain. But no doubt, all those limited projects have shown very promising results. In case of Pakistan, the prolific expedition to hunt for hydrates was made in 1998 with Pak-Germany collaboration. The expedition revealed that the gas hydrates buried under Makran Coast in the Arabian Sea are around 29% saturated with methane gas; 7.5% free gas also exists with hydrates. Further, the BSRs in the Arabian Sea are traced at the depth of 500 to 800 m below the seafloor. On the other hand, demand for natural gas rises by 60 to 75 MMCFD every year in Pakistan; therefore, the development of natural gas hydrates can be a prudent solution to meet the future energy demand of whole country. The novelty of this paper is the incorporation of satellite imaging technology to prove natural gas hydrate potential in the maritime vicinity of Pakistan. [ABSTRACT FROM AUTHOR]

[Display omitted] • First-time DOE applied in a piston horizontal reactor for hydrate formation study. • RSM approach uncovers key factor interactions, optimizing hydrate formation. • V S /V R ratio emerges as the most influential factor in CH 4 hydrate formation. • Optimization yields 97.38 % conversion, 0.983 mol gas uptake, within 3 h. Gas hydrate formation is a complex process influenced by various factors, including the gas-liquid interfacial area, solution volume, and gas surplus, leading to diverse outcomes in hydrate formation capacity and kinetics, as documented in numerous literature sources. This study employs a sequential experimental design for response surface optimization to investigate key factors and their interactions affecting a formation system of mixed methane-THF hydrate at 298.2 K and 9.2 MPa. The experimental setup involves the use of 0.03 wt% L-Tryptophan (L-Trp) as a kinetic promoter in an adjustable-length horizontal tubular batch crystallizer. Three independent variables were investigated: crystallizer length, solution to crystallizer volume ratio (V S /V R), and supplementary gas reservoir volume V res. Their effects on four crucial responses, water to hydrate conversion, gas uptake, normalized rate of hydrate formation (NR 30), and time to achieve 90 % of overall gas uptake (t 90) were analyzed with the aim of informing system design and scaling. Key findings indicate that the V S /V R at 0.54, combined with an optimized V res and crystallizer length, significantly enhances gas uptake and hydrate formation kinetics, achieving high hydrate formation capacity within three hours. Interestingly, the V S /V R ratio emerged as the most influential factor across all measured responses. Model validation affirmed the reliability of the findings with small percentage errors, providing a robust foundation for system design, upscaling, and applications in methane hydrate-based energy storage technology. [ABSTRACT FROM AUTHOR]

Methane hydrates are one of the most powerful reserves of unconventional sources of hydrocarbons. This is clearly evidenced by the forecast estimates of world volumes of methane in the form of gas hydrates, which many times exceed the total resources of traditional natural gas. In the foreseeable future, natural methane hydrates should significantly increase the current energy balance of natural hydrocarbon fuel resources. Progress in their study can be ensured by the dialectical unity of theoretical and experimental research, focused mainly on thermodynamics, kinetics and their physical properties, as well as on the development and testing of technologies for methane production from gas hydrate deposits. Existing methods of developing gas hydrates involve their preliminary dissociation into gas and water. At the same time, the deposit depressurization method is considered the most promising. However, there is still no commercially attractive technology for the development of gas hydrates. The article presents an overview of gas hydrate research in the world, provides an analysis of prospective methods of their development, summarizes the advantages and disadvantages of current research and industrial attempts to extract methane from aqua deposits of gas hydrates, and evaluates the prospects of various technologies. Currently known examples of research and industrial development of gas hydrate deposits have demonstrated a number of problems. However, encouraging results were obtained. The analysis of processes in the oil and gas production industry shows that profitable industrial production of natural gas from gas hydrate deposits will be possible after an effective breakthrough technology appears on the market.

• Studied the axial annulus in situ hydrocyclone desander. • Realizing in-situ sand removal and backfilling the seabed. • The separation efficiencies of sand and NGH reach 84.7 % and 76.1 %, respectively. • Maximum pressure drop of 320.7 kPa, which was only 2.1 % of the environmental pressure (15.2 MPa). Natural Gas Hydrates (NGH) offer a promising solution to the global energy shortage. Nevertheless, the extraction of NGH encounters complexities and challenges in marine environments, necessitating the systematic separation of seawater, NGH particles, and sand, as well as the backfilling of sand to prevent damage to the seabed geological structure. Leveraging computational fluid dynamics (CFD) studies on operational and structural parameters, we have developed an optimized Axial Annulus In-situ Hydrocyclone Desander (AAIHD-2). By enhancing the radial forces exerted and extending the suspension time of particles within the flow field, the separation efficiencies of sand and NGH reached 84.7 % and 76.1 %, respectively. Increasing the length of the separation zone proves advantageous in boosting the separation efficiency of both sand and NGH. Notably, while the sand separation efficiency increases with higher flow rate, the NGH separation efficiency decreases. AAIHD-2 exhibits a maximum pressure drop of 320.7 kPa, constituting a mere 2.1 % of the environmental pressure (15.2 MPa), thereby ensuring the preservation of NGH equilibrium throughout the extraction process. This study is poised to facilitate the efficient separation of NGH and the backfilling of sand in order to enable the safe extraction of seabed NGH. [ABSTRACT FROM AUTHOR]

• Detection of cold seep methane plumes using optimal images. • A deep learning method for methane plumes detection is proposed. • A new YOLOv5 network is proposed. Natural gas hydrates stored in the subsurface seabed of continental margins are one of the most important carbon reservoirs on Earth. Research on natural gas hydrates is of great significance to global warming and ecological protection. Methane plumes caused by crustal dynamics are usually considered as a sign of existence of natural gas hydrates. Detection of methane plumes thus becomes the first step of cold seep research. This paper conducts comprehensive research on detection of methane plumes based on deep learning methods and optical images. First, we proposed a method of creating high quality and balanced datasets for methane plumes detection tasks using open-source videos. We then proposed a FMAW-YOLOv5s method for methane plumes detection. The FMAW-YOLOv5s method improves the traditional YOLOv5s in design of backbone network, neck network and loss function. The FMAW-YOLOv5s method can realize accurate and fast detection of methane plumes with a precision of 96.9% and FPS of 141.7. The lightweight feature of FMAW-YOLOv5s also enables the deployment in edge computing devices such as AUVs and ROVs. This research can not only promote the study of cold seep activities, but also provide meaningful insights for detection of other underwater events such as gas pipelines leakage. [ABSTRACT FROM AUTHOR]

Natural gas hydrates have garnered widespread attention as a high-quality energy resource. Recent offshore extraction experiences suggest that depressurization is a technically mature and economically viable option. However, challenges such as reservoir temperature reduction, reservoir subsidence, secondary hydrate formation, and insufficient dynamics in later-stage hydrate decomposition still require improvements to the depressurization method. This study, based on field data from Japan's first offshore natural gas hydrate extraction, utilizes a self-developed numerical simulator to model and validate reservoirs at the field scale. Long-term production rate stability, total production, secondary hydrate formation, reservoir subsidence, evolution of permeability, and temperature-pressure paths were analyzed and optimized for the three mainstream depressurization modes: steady depressurization, stepwise depressurization, and cyclic depressurization. The results indicate that, under the condition of equal total work done throughout the entire depressurization process, steady depressurization with an effectively lower depressurization rate is the optimal choice. Cyclic depressurization, due to the formation of secondary hydrates reducing the permeability of certain reservoir zones, adversely affects gas production efficiency during the long-term stable production phase. This study enhances insights into the coupled evolution of multiple physical fields during the depressurization of offshore natural gas hydrates, providing valuable guidance for future on-site extraction plan designs. • Modeled and validated the accuracy of heterogeneous hydrate reservoirs. • Evaluation of different depressurization modes using a self-developed simulator. • Analyzed temperature-pressure paths during hydrate decomposition. • Optimized mainstream depressurization modes using multiple field-relevant indicators. [ABSTRACT FROM AUTHOR]

Gas hydrate is an ice-like form of water containing gas, in nature mostly methane (CH 4), which requires moderate pressures and low temperatures. The replacement of CH 4 by CO 2 , which also forms a hydrate, could allow CH 4 production from hydrate while sequestering CO 2. A number of recent studies have focused on theoretical background, experimental simulations, and engineering approaches related to CH 4 -CO 2 exchange in hydrates. We here investigate a key geologic constraint for possible CH 4 -CO 2 exchange in sub-seafloor reservoirs, hydrate stability. We analyze seismic data and gas hydrate system models from the Pegasus Basin east of New Zealand, a region with evidence for abundant gas hydrates. Pressure-temperature conditions beneath the seafloor need to be within the stability fields for both CH 4 hydrate and hydrate from the resulting gas mix after CO 2 injection. Based on experimental and theoretical studies, we consider 64% a benchmark for maximum achievable CH 4 replacement by CO 2 , resulting in a mix of 64% CO 2 – 36% CH 4 , in hydrate. Down to a water depth of 1087 m, hydrate from this gas mix is stable within the entire CH 4 hydrate stability field. A gap develops in deeper water with the base of gas hydrate stability (BGHS) for CH 4 being deeper than for the 64% CO 2 – 36% CH 4 mix. In nature, most mechanisms for CH 4 hydrate formation favor high saturation near the BGHS. For an evaluation of possible CH 4 -CO 2 exchange, it is therefore important to investigate mixed-gas hydrate stability near the CH 4 -BGHS and to identify CH 4 hydrates closer to the seafloor. • CH 4 (methane)-CO 2 exchange may allow carbon-neutral production of CH 4 from hydrate. • Stability for hydrates from CO 2 and CH 4 gas mixes beneath the seafloor modeled. • Assumed 64% CO 2 - 36% CH 4 mix as final CO 2 /CH 4 ratio after CH 4 replacement. • For water depth <1087 m, hydrate from this gas mix is more stable than CH 4 hydrate. • In deeper water, CH 4 hydrate partly below hydrate stability field for this gas mix. [ABSTRACT FROM AUTHOR]

ABSTRACT: Natural gas hydrates (NGHs) are globally recognized as an important type of strategic alternative energy due to their high combustion efficiency, cleanness, and large amounts of resources. The NGHs reservoirs in the South China Sea (SCS) mainly consist of clayey silts. NGHs reservoirs of this type boast the largest distribution range and the highest percentage of resources among NGHs reservoirs in the world. However, they are more difficult to exploit than sandy reservoirs. The China Geological Survey successfully carried out two NGHs production tests in the Shenhu Area in the northern SCS in 2017 and 2020, setting multiple world records, such as the longest gas production time, the highest total gas production, and the highest average daily gas production, as well as achieving a series of innovative theoretical results. As suggested by the in-depth research on the two production tests, key factors that restrict the gas production efficiency of hydrate dissociation include reservoir structure characterization, hydrate phase transition, multiphase seepage and permeability enhancement, and the simulation and regulation of production capacity, among which the hydrate phase transition and seepage mechanism are crucial. Study results reveal that the hydrate phase transition in the SCS is characterized by low dissociation temperature, is prone to produce secondary hydrates in the reservoirs, and is a complex process under the combined effects of the seepage, stress, temperature, and chemical fields. The multiphase seepage is controlled by multiple factors such as the physical properties of unconsolidated reservoirs, the hydrate phase transition, and exploitation methods and is characterized by strong methane adsorption, abrupt changes in absolute permeability, and the weak flow capacity of gas. To ensure the long-term, stable, and efficient NGHs exploitation in the SCS, it is necessary to further enhance the reservoir seepage capacity and increase gas production through secondary reservoir stimulation based on initial reservoir stimulation. With the constant progress in the NGHs industrialization, great efforts should be made to tackle the difficulties, such as determining the micro-change in temperature and pressure, the response mechanisms of material-energy exchange, the methods for efficient NGHs dissociation, and the boundary conditions for the formation of secondary hydrates in the large-scale, long-term gas production.©2022 China Geology Editorial Office.

ABSTRACT: How natural gas hydrates nucleate and grow is a crucial scientific question. The research on it will help solve practical problems encountered in hydrate accumulation, development, and utilization of hydrate related technology. Due to its limitations on both spatial and temporal dimensions, experiment cannot fully explain this issue on a micro-scale. With the development of computer technology, molecular simulation has been widely used in the study of hydrate formation because it can observe the nucleation and growth process of hydrates at the molecular level. This review will assess the recent progresses in molecular dynamics simulation of hydrate nucleation and growth, as well as the enlightening significance of these developments in hydrate applications. At the same time, combined with the problems encountered in recent hydrate trial mining and applications, some potential directions for molecular simulation in the research of hydrate nucleation and growth are proposed, and the future of molecular simulation research on hydrate nucleation and growth is prospected.©2022 China Geology Editorial Office.

ABSTRACT: Large amounts of gas hydrate are distributed in the northern slope of the South China Sea, which is a potential threat of methane leakage. Aerobic methane oxidation by methanotrophs, significant methane biotransformation that occurs in sediment surface and water column, can effectively reduce atmospheric emission of hydrate-decomposed methane. To identify active aerobic methanotrophs and their methane oxidation potential in sediments from the Shenhu Area in the South China Sea, multi-day enrichment incubations were conducted in this study. The results show that the methane oxidation rates in the studied sediments were 2.03–2.36 μmol/gdw/d, which were higher than those obtained by sediment incubations from other areas in marine ecosystems. Thus the authors suspect that the methane oxidation potential of methanotrophs was relatively higher in sediments from the Shenhu Area. After the incubations family Methylococcaea (type I methanotrophs) mainly consisted of genus Methylobacter and Methylococcaea_Other were predominant with an increased proportion of 70.3%, whereas Methylocaldum decreased simultaneously in the incubated sediments. Collectively, this study may help to gain a better understanding of the methane biotransformation in the Shenhu Area.©2022 China Geology Editorial Office.

Experts have identified natural gas hydrates, which are found in the shallow seabed and beneath permafrost regions, as an energy source (mostly methane) that is greener than other petroleum fuel resources. With their worldwide distribution and abundance, gas hydrates have vast potential to become the next pillar of the energy industry. Although no entity has established methane extraction from hydrates at a commercial scale yet, extensive laboratory experiments have introduced several extraction strategies. Methods such as depressurization, thermal stimulation, and inhibitor injection are likely to disturb seabed integrity, which may result in catastrophic consequences. However, the CO2 replacement method is inferred to be preserving the seabed stability, offering an opportunity to reduce anthropogenic CO2 emissions safely. In this paper, we provide a comprehensive review of the progress of experimental work in developing methane-extraction methods for gas hydrate reservoirs. Depressurization combined with thermal stimulation can be proposed as a viable methane extraction method based on laboratory-scale experiments, however, a sustainable extraction method is yet to be developed to field-scale when both economic and environmental perspectives are considered. A handful of field production runs have delivered positive outcomes to establish the exploitability of natural hydrate reservoirs, but thorough investigations and scientific collaborations are needed to develop hydrate accumulations as a commercially viable energy source.

The replacement of methane with a theoretically equal quantity of carbon dioxide, probably represents the most promising solution for natural gas hydrate exploitation. However, the real efficiency is far from the ideal value. This article aims to focus the attention on the thermodynamic area considered suitable for replacement. Because the formation and dissociation of hydrates always show differences between each other and, in particular, the formation always requires more severe conditions to occur, the region effectively suitable for replacement is still more narrow than what currently believed and consists of the area between the dissociation curve of methane hydrates and the formation curve of CO 2 hydrates. The present hypothesis was confirmed by carrying out the replacement process both above and below this latter curve. It was found that the methane recovery was more than one order of magnitude higher in the first case: 43.32 against 4.19 vol%. [Display omitted] [ABSTRACT FROM AUTHOR]

Natural gas hydrates have been an unconventional source of energy since the beginning of this century. Gas-hydrate-filled reservoirs show higher resistivity values compared with water-filled sediments. Their presence can be detected using marine controlled-source electromagnetic methods. We classify acquisition configurations into stationary and moving receiver configurations, which are described in terms of the design group, the operational details, and where they have been used successfully in the field for natural gas hydrate exploration. All configurations showed good numerical results for the detection of a 700 m long gas hydrate reservoir buried 200 m below the seafloor, but only the stationary configurations provided data that can be used to estimate the horizontal boundaries of the resistive part of the reservoir when the burial depth is known from seismic data. We discuss the operational steps of the configurations and provide the steps on how to choose a suitable configuration. Different CSEM configurations were used together with seismic data to estimate the edge of the gas hydrate reservoir and the total volume of the gas hydrates, to optimize the drilling location, to increase production safety, and to improve geological interpretations. It seems that CSEM has become a reliable method to aid in the decision-making process for gas hydrate reservoir appraisal and development. [ABSTRACT FROM AUTHOR]

The study of hydrate formation plugging has been more frequently studied in the gathering and recovery process at home and abroad, but the study of hydrate formation plugging under deepwater drilling conditions is rarely done, and the comprehensive assessment of hydrate formation plugging risk still needs to be further studied. During deepwater drilling, the wellbore is susceptible to blockage caused by hydrates and induces a series of downhole accident risks. The theoretical and experimental aspects of hydrate generation and plugging risk assessment during drilling, start-up and kill well of hydrates under low temperature and high pressure conditions in the wellbore during deepwater drilling were investigated. The types of gas hydrate generation risks were systematically introduced. The formation risk assessment environment of gas hydrate was divided into two situations: drilling in natural gas bearing formation wellbore and drilling in normal deepwater wellbore. Current hydrate generation risk prediction models were used for deepwater drilling: based on V-P model derivation, based on complex dissolution theory, based on intelligent algorithms, etc. Hydrate detection methods mainly include optical-based detection, ultrasound-based detection, electrical-based detection, CT-based techniques, and MRI-based techniques were used for experimental assessment of hydrate formation risk. Hydrate assessment methods based mainly on supercooling and dimensionless construction parameters were used for the quantitative hydrate formation risk assessment. A comprehensive analysis shows that the existing hydrate formation risk prediction model in deepwater drilling process is complicated in calculation and cannot be well fitted by deepwater drilling conditions; and the risk of blockage formation in deepwater drilling cycle, start-up, shut in well and kill well, and other complex conditions cannot be well reduced by hydrate formation risk experimental evaluation simulation. The research project on hydrate formation risk assessment and treatment methods under multi-boundary conditions in deepwater drilling was combined with the research focus on the hydrate formation risk of natural gas in deepwater drilling in the future, as a sub-project of the research on key technologies for drilling and completing deepwater gas field cluster development in China Southeast Hainan. [ABSTRACT FROM AUTHOR]

Copyright of Journal of China University of Petroleum is the property of China University of Petroleum and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of China University of Petroleum is the property of China University of Petroleum and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

For the production of natural gas hydrates with the depressurization method, safety problems may be caused by the existence of hydrates and microscale sands in the flow channels. Thus, it is particularly important to study the influence of microscale sands on the hydrates. For this reason, the hydrate formation and decomposition experiments in the presence of microscale sands were performed with tetrahydrofuran (THF) as an alternative medium. In this way, the morphological structure of hydrates was observed and the effect of microscale sands was analyzed. The results show that the microscale sands coexisting with THF hydrates are present in three forms, i.e., free state, adhesive state, and wrapped state. The presence of microscale sands will affect the agglomeration of hydrates, and the microscale sands entrapped in the hydrate layer during deposition will change the structure and mechanical properties of the hydrate layer. What's more, the microscale sands will accelerate the decomposition of hydrates, change the shedding way of hydrate deposit layer in the pipeline, and further affect the flow safety in the pipelines. Generally, the research results could provide reference for the analysis on deposition characteristics of the hydrates within the flow channels and the flow safety assessment thereof.

This research explores the geomechanical challenges associated with gas hydrate extraction in submarine slope zones, a setting posing a high risk of significant geological calamities. We investigate slope and wellbore deformations driven by hydrate decomposition within a subsea environment. Utilizing Abaqus, a fluid-solid-thermal multi-field coupling model for gas hydrate reservoirs was created. Hydrate decomposition during drilling is minimal, resulting in minor formation deformation near the wellbore. However, a year of hydrate production caused a maximum displacement of up to 7 m in the wellbore and formation, highlighting the risk of submarine landslides. This indicates the need for meticulous surveillance of formation subsidence and wellhead equipment displacement. In the aftermath of a hydrate-induced submarine landslide, both the hydrate layer and the overlying strata descend together, inflicting considerable damage on the formation and wellbore. Our study presents a holistic examination of the interplay between environmental geomechanics risks and engineering structure risks for submarine slope instability and wellbore stability during hydrate development, providing crucial insights for enhancing safety measures in hydrate drilling and production, and ensuring wellbore stability.

This paper demonstrates the applicability of machine learning algorithms in sand production problems with natural gas hydrate (NGH)-bearing sands, which have been regarded as a grave concern for commercialization. The sanding problem hinders the commercial exploration of NGH reservoirs. The common sand production prediction methods need assumptions for complicated mathematical derivations. The main contribution of this paper was to introduce machine learning into the prediction sand production by using data from laboratory experiments. Four main machine learning algorithms were selected, namely, K-Nearest Neighbor, Support Vector Regression, Boosting Tree, and Multi-Layer Perceptron. Training datasets for machine learning were collected from a sand production experiment. The experiment considered both the geological parameters and the sand control effect. The machine learning algorithms were mainly evaluated according to their mean absolute error and coefficient of determination. The evaluation results showed that the most accurate results under the given conditions were from the Boosting Tree algorithm, while the K-Nearest Neighbor had the worst prediction performance. Considering an ensemble prediction model, the Support Vector Regression and Multi-Layer Perceptron could also be applied for the prediction of sand production. The tuning process revealed that the Gaussian kernel was the proper kernel function for improving the prediction performance of SVR. In addition, the best parameters for both the Boosting Tree and Multi-Layer Perceptron were recommended for the accurate prediction of sand production. This paper also involved one case study to compare the prediction results of the machine learning models and classic numerical simulation, which showed the capability of machine learning of accurately predicting sand production, especially under stable pressure conditions. [ABSTRACT FROM AUTHOR]