Shear strength of hydrate-bearing sediment is an essential parameter for assessing landslide potential ofhydrate reservoirs under exploration conditions. However, the characteristics and simulation of thisshear streng...Shear strength of hydrate-bearing sediment is an essential parameter for assessing landslide potential ofhydrate reservoirs under exploration conditions. However, the characteristics and simulation of thisshear strength under varying dissociation conditions have not been thoroughly investigated. To this end,a series of triaxial compression tests were first carried out on sediments with varying initial hydratesaturations along dissociation pathways. Combining measured data with microscale analysis, the underlyingmechanism for the evolution of shear strength in hydrate-bearing sediment was studied undervarying partial dissociation pathways. Moreover, a shear strength model for hydrate-bearing sedimentwas proposed, taking into account the hydrate saturation and the unhydrated water content. Apart fromthe parameters derived from the hydrate characteristic curve, only one additional model parameter isrequired. The proposed model was validated using measured data on hydrate sediments. The resultsindicate that the proposed model can effectively capture the shear strength behavior of hydrate-bearingsediment under varying dissociation paths. Finally, a sensitivity analysis of the model parameters wasconducted to characterize the proposed model.展开更多
Natural gas hydrate is a clean energy source with substantial resource potential.In contrast to conventional oil and gas,natural gas hydrate exists as a multi-phase system consisting of solids,liquids,and gases,which ...Natural gas hydrate is a clean energy source with substantial resource potential.In contrast to conventional oil and gas,natural gas hydrate exists as a multi-phase system consisting of solids,liquids,and gases,which presents unique challenges and complicates the mechanisms of seepage and exploitation.Both domestic and international natural gas hydrate production tests typically employ a single-well production model.Although this approach has seen some success,it continues to be hindered by low production rates and short production cycles.Therefore,there is an urgent need to explore a new well network to significantly increase the production of a single well.This paper provides a comprehensive review of the latest advancements in natural gas hydrate research,including both laboratory studies and field tests.It further examines the gas production processes and development outcomes for single wells,dual wells,multi-branch wells,and multi-well systems under conditions of depressurization,thermal injection,and CO_(2) replacement.On this basis,well types and well networks suitable for commercial exploitation of natural gas hydrate were explored,and the technical direction of natural gas hydrate development was proposed.The study shows that fully exploiting the flexibility of complex structural wells and designing a well network compatible with the reservoir is the key to improving production from a single well.Moreover,multi-well joint exploitation is identified as an effective strategy for achieving large-scale,efficient development of natural gas hydrate.展开更多
During the production of natural gas hydrates,micron-sized sand particles coexist with hydrate within the transportation pipeline,posing a significant threat to the safety of pipeline flow.However,the influence of san...During the production of natural gas hydrates,micron-sized sand particles coexist with hydrate within the transportation pipeline,posing a significant threat to the safety of pipeline flow.However,the influence of sand particles on hydrate formation mechanisms and rheological properties remains poorly understood.Consequently,using a high-pressure reactor system,the phase equilibrium conditions,hydrate formation characteristics,hydrate concentration,and the slurry viscosity in micron-sized sand system are investigated in this work.Furthermore,the effects of sand particle size,sand concentration,and initial pressure on these properties are analyzed.The results indicate that a high concentration of micron-sized sand particles enhances the formation of methane hydrates.When the volume fraction of sand particles exceeds or equals 3%,the phase equilibrium conditions of the methane hydrate shift to the left relative to that of the pure water system(lower temperature,higher pressure).This shift becomes more pronounced with smaller particle sizes.Besides,under these sand concentration conditions,methane hydrates exhibit secondary or even multiple formation events,though the formation rate decreases.Additionally,the torque increases significantly and fluctuates considerably.The Roscoe-Brinkman model yields the most accurate slurry viscosity calculations,and as sand concentration increases,both hydrate concentration and slurry viscosity also increase.展开更多
The commercial exploitation of natural gas hydrates is currently facing several challenges,including low production rates,limited recovery areas,and brief periods of continuous production.To address these issues,we pr...The commercial exploitation of natural gas hydrates is currently facing several challenges,including low production rates,limited recovery areas,and brief periods of continuous production.To address these issues,we propose a novel dual-enhanced stimulation(DES)method for marine hydrate reservoirs.This method involves injecting a special slurry that solidifies into porous,high-permeability,and highstrength slurry veins.These veins not only enhance permeability,allowing for faster gas and water flow,but also improve reservoir stability.This study experimentally investigated the split grouting of clayey-silty sediments with dual-enhanced slurry to assess the feasibility of DES and to explo re the slurry diffusion mechanism and micro-pore structure of the veins.The results showed that split grouting with dual-enhanced slurry exhibited frequent fracture initiation with quick pressure spikes and sharp declines,suggesting shorter fractures in clayey-silty sediments.As vertical stress increased,the primary diffusion direction of the dual-enhanced slurry shifted from horizontal to vertical,aligning with fracture propagation patterns observed during fracturing.Unlike hydraulic fracturing in hard rocks,split grouting in clayey-silty sediments encountered more difficult conditions.These veins formed through a recurring cycle of splitting into fractures and filling with slurry,occurring more frequently in weaker sediments with slower injection rates and higher vertical stress.Increased vertical stress hindered slurry vein diffu sion,easily resulting in compaction grouting near the grouting pipe.Additionally,three-dimensional laser scanning of the veins showed that those formed through split grouting were continuous and stable,with their thickness decreasing as diffusion distance increased.The morphology of these veins was shaped by factors such as grouting rate,formation stress,and elastic modulus,with higher rates and elastic moduli facilitating the formation of complex vein networks.Mercury intrusion porosimetry demonstrated that the DES method resulted in veins with consistent effective porosity between 65%and70%and median pore sizes of 11-15μm across different locations.These veins formed a well-connected porous network of smaller pores,significantly enhancing both permeability and sand control.The research findings validate the effectiveness of the DES method for marine hydrate reservoirs,providing a strategy for the safe and efficient exploitation of NGH resources.展开更多
The flow behaviors of gas and water in hydrate-bearing sediments(HBS)are significantly affected by the threshold pressure gradient(TPG).During long-term natural gas hydrates(NGHs)mining,there exists creep deformation ...The flow behaviors of gas and water in hydrate-bearing sediments(HBS)are significantly affected by the threshold pressure gradient(TPG).During long-term natural gas hydrates(NGHs)mining,there exists creep deformation in HBS,which significantly alters pore structures,makes the flow path of fluid more complex,and leads to changes in TPG.Thus,clarifying the evolution of TPG in HBS during creep is essential for NGH production,but it also confronts enormous challenges.In this study,based on the nonlinear creep constitutive model,a novel theoretical TPG model of HBS during creep is proposed that considers pore structures and hydrate pore morphology.The established model is validated against experimental data,demonstrating its ability to capture the evolution of TPG and permeability in HBS during creep.Additionally,the relationship between initial hydrate saturation and TPG of HBS during creep is revealed by sensitivity analysis.The creep strain increases with the decrease in initial hydrate saturation,leading to a greater TPG and a lower permeability.The evolution of TPG at the stable creep stage and the accelerated creep stage is primarily controlled by the Kelvin element and visco-plastic element,respectively.This novel proposed model provides a mechanistic understanding of TPG evolution in HBS during creep,and it is of great significance to optimize the exploitation of NGHs.展开更多
As a kind of novel environmental-friendly surfactant,Gemini surfactant has attracted extensive research interests in its effects on gas hydrate formation.We investigated the effects of dioctyl sodium sulfosuccinate(AO...As a kind of novel environmental-friendly surfactant,Gemini surfactant has attracted extensive research interests in its effects on gas hydrate formation.We investigated the effects of dioctyl sodium sulfosuccinate(AOT)on the formation thermodynamics/kinetics of CH_(4)and CO_(2)hydrates.Experimental results indicate that while AOT does not exhibit significant thermodynamic promotion for hydrate formation,it demonstrates favorable kinetic promotion effects.Its promotion effect surpasses that of the traditional kinetic promoter SDS and can enhance the gas storage capacity of hydrates.Utilizing the Chen-Guo hydrate model and adsorption kinetic model,we established a kinetic model for AOT with a predictive deviation of 7.17%and fitted key parameters accordingly.展开更多
Hydraulic fracturing technology has played an important role in the exploitation of unconventional oil and gas resources,however,its application to gas hydrate reservoirs has been rarely studied.Currently,there is sti...Hydraulic fracturing technology has played an important role in the exploitation of unconventional oil and gas resources,however,its application to gas hydrate reservoirs has been rarely studied.Currently,there is still limited understanding of the propagation and extension of fractures around the wellbore during the fracturing process of horizontal wells in hydrate reservoirs,as well as the stress interference patterns between fractures.This study simulates hydraulic fracturing processes in hydrate reservoirs using a fluidsolid coupling discrete element method(DEM),and analyzes the impacts of hydrate saturation and geological and engineering factors on fracture extension and stress disturbance.The results show that hydraulic fracturing is more effective when hydrate saturation exceeds 30%and that fracture pressure increases with saturation.The increase in horizontal stress differential enhances the directionality of fracture propagation and reduces stress disturbance.The distribution uniformity index(DUI)reveals that injection pressure is directly proportional to the number of main fractures and inversely proportional to fracturing time,with fracturing efficiency depending on the spacing between injection points and the distance between wells.This work may provide reference for the commercial exploitation of natural gas hydrates.展开更多
Natural gas hydrates widely accumulate in submarine sediments composed of clay minerals.However,due to the complex physiochemistry and micron-sized particles of clay minerals,their effects on methane hydrate(MH)format...Natural gas hydrates widely accumulate in submarine sediments composed of clay minerals.However,due to the complex physiochemistry and micron-sized particles of clay minerals,their effects on methane hydrate(MH)formation and dissociation are still in controversy.In this study,montmorillonite and illite were separately mixed with quartz sand to investigate their effects on MH formation and dissociation.The microstructure of synthesized samples was observed by cryo-SEM innovatively to understand the effects of montmorillonite and illite on MH phase transition in micron scale.Results show that montmorillonite and illite both show the inhibition on MH formation kinetics and water-to-hydrate conversion,and illite shows a stronger inhibition.The 10 wt%montmorillonite addition significantly retards MH formation rate,and the 20 wt%montmorillonite has a less inhibition on the rate.The increase of illite mass ratio(0-20 wt%)retards the rate of MH formation.As the content of clay minerals increase,the water-to-hydrate conversion decreases.Cryo-SEM images presented that montmorillonite aggregates separate as individual clusters while illite particles pack as face-to-face configuration under the interaction with water.The surface-overlapped illite aggregates would make sediments pack tightly,hinder the contact between gas and water,and result in the more significant inhibition on MH formation kinetics.Under the depressurization method,the addition of clay minerals facilitates MH dissociation rate.Physicochemical properties of clay minerals and MH distribution in the pore space lead to the faster dissociation rate in clay-containing sediments.The results of this study would provide beneficial guides on geological investigations and optimizing strategies of natural gas production in marine hydrate-bearing sediments.展开更多
Gas hydrate(GH)is an unconventional resource estimated at 1000-120,000 trillion m^(3)worldwide.Research on GH is ongoing to determine its geological and flow characteristics for commercial produc-tion.After two large-...Gas hydrate(GH)is an unconventional resource estimated at 1000-120,000 trillion m^(3)worldwide.Research on GH is ongoing to determine its geological and flow characteristics for commercial produc-tion.After two large-scale drilling expeditions to study the GH-bearing zone in the Ulleung Basin,the mineral composition of 488 sediment samples was analyzed using X-ray diffraction(XRD).Because the analysis is costly and dependent on experts,a machine learning model was developed to predict the mineral composition using XRD intensity profiles as input data.However,the model’s performance was limited because of improper preprocessing of the intensity profile.Because preprocessing was applied to each feature,the intensity trend was not preserved even though this factor is the most important when analyzing mineral composition.In this study,the profile was preprocessed for each sample using min-max scaling because relative intensity is critical for mineral analysis.For 49 test data among the 488 data,the convolutional neural network(CNN)model improved the average absolute error and coefficient of determination by 41%and 46%,respectively,than those of CNN model with feature-based pre-processing.This study confirms that combining preprocessing for each sample with CNN is the most efficient approach for analyzing XRD data.The developed model can be used for the compositional analysis of sediment samples from the Ulleung Basin and the Korea Plateau.In addition,the overall procedure can be applied to any XRD data of sediments worldwide.展开更多
Morphology and growth rate of carbon dioxide hydrate on the interface between liquid carbon dioxide and humic acid solutions were studied in this work.It was found that after the growth of the hydrate film at the inte...Morphology and growth rate of carbon dioxide hydrate on the interface between liquid carbon dioxide and humic acid solutions were studied in this work.It was found that after the growth of the hydrate film at the interface,further growth of hydrate due to the suction of water in the capillary system formed between the wall of the cuvette and the end boundary of the hydrate layer occurs.Most probably,substantial effects on the formation of this capillary system may be caused by variations in reactor wall properties,for example,hydrophobic-hydrophilic balance,roughness,etc.We found,that the rate of CO_(2) hydrate film growth on the surface of the humic acid aqueous solution is 4-fold to lower in comparison with the growth rate on the surface of pure water.We suppose that this is caused by the adsorption of humic acid associates on the surface of hydrate particles and,as a consequence,by the deceleration of the diffusion of dissolved carbon dioxide to the growing hydrate particle.展开更多
An efficient acetic acid mediated metal-free oxidative C—H cross coupling of imidazo[1,2-a]pyridines with glyoxal hydrates has been developed under air atmosphere.The present protocol exhibits broad substrate scope,g...An efficient acetic acid mediated metal-free oxidative C—H cross coupling of imidazo[1,2-a]pyridines with glyoxal hydrates has been developed under air atmosphere.The present protocol exhibits broad substrate scope,good functional group tolerance,and enables the construction of a series of 1,2-dicarbonyl imidazo[1,2-a]pyridines in good yields.The reaction mechanism studies suggest that the reactions proceed through the electrophilic substitution and subsequent oxidation pathway.展开更多
Natural gas hydrate widely exists in the South China Sea as clean energy.A three-phase transition layer widely exists in low permeability Class I hydrates in the Shenhu offshore area.Therefore,taking into account the ...Natural gas hydrate widely exists in the South China Sea as clean energy.A three-phase transition layer widely exists in low permeability Class I hydrates in the Shenhu offshore area.Therefore,taking into account the low-permeability characteristics with an average permeability of 5.5 mD and moderate heterogeneity,a 3-D geological model of heterogeneous Class I hydrate reservoirs with three-phase transition layers is established by Kriging interpolation and stochastic modeling method,and a numerical simulation model is used to describe the depressurization production performance of the reservoir.With the development of depressurization,a specific range of complete decomposition zones appear both in the hydrate and transition layers.The entire decomposition zone of the whole reservoir tends to outward and upward diffusion.There is apparent methane escape in the three-phase transition layer.Due to the improvement of local permeability caused by the phase transition of hydrate dissociation,some methane accumulation occurs at the bottom of the hydrate layer,forming a local methane enrichment zone.The methane migration trends in reservoirs are mainly characterized by movement toward production wells and hydrate layers under the influence of gravity.However,due to the permeability limitation of hydrate reservoirs,many fluids have not been effectively produced and remain in the reservoir.Therefore,to improve the effective pressure drop of the reservoir,the perforation method and pressure reduction method were optimized by analyzing the influencing factors based on the gas production rate.The comparative study demonstrates that perforating through the free gas layer combined with one-time depressurization can enhance the effective depressurization and improve production performance.The gas production rate from perforating through the free gas layer can be twice as high as that from perforating through the transition layer.This study can provide theoretical support for the utilization of marine energy.展开更多
Field tests have demonstrated that depressurization with controlled sand production is an effective technique for natural gas hydrate extraction.Variations in depositional environments and processes result in signific...Field tests have demonstrated that depressurization with controlled sand production is an effective technique for natural gas hydrate extraction.Variations in depositional environments and processes result in significant heterogeneity within subsea natural gas hydrate-bearing sediments.However,the influence of permeability heterogeneity on production performance during depressurization with controlled sand production remains inadequately understood.In this study,a multiphase,multi-component mathematical model is developed to simulate depressurization with controlled sand production in methane hydrate-bearing sediments,incorporating geological conditions representative of unconsolidated argillaceous siltstone hydrate deposits in the Shenhu area of the South China Sea.The effects of permeability heterogeneity-specifically,horizontal autocorrelation length and global permeability heterogeneity-on production performance during depressurization with sand production are investigated using geostatistical modeling combined with finite difference method based numerical simulations.Results show that as the horizontal autocorrelation length of permeability distribution increases,cumulative gas production first rises and then declines,reaching its peak at λ_(Dh)=0.1,whereas sand production steadily increases.In addition,higher formation permeability heterogeneity results in increased cumulative gas and sand production,suggesting that greater heterogeneity promotesmethane hydrate decomposition and gas recovery.These findings can offer valuable insights for optimizing future field development of hydrate-bearing sediments by depressurization with controlled sand production.展开更多
Weak cementation between natural gas hydrates and mud–sand seriously affects the solid-fluidized mining of natural gas hydrates. In this study, we analyze the debonding of natural gas hydrate sediment (NGHS) particle...Weak cementation between natural gas hydrates and mud–sand seriously affects the solid-fluidized mining of natural gas hydrates. In this study, we analyze the debonding of natural gas hydrate sediment (NGHS) particles by applying the principle of spiral-cyclone coupling separation. To achieve this, weakly cemented NGHS particle and mechanical models were established. In the flow field of the spiral-cyclone flow-coupling separator, the motion characteristics of the weakly cemented NGHS particles and the destruction process of the cementation bond were analyzed. The destruction of the bonds mainly occurred in the spiral channel, and the destruction efficiency of the bonds was mainly affected by the rotational speed. Collision analysis of the particles and walls showed that when the velocity is 10–16 m·s^(−1), the cementation bond can be broken. The greater the speed, the better the effect of the bond fracture. The breaking rate of the cementation bonds was 85.7%. This study is significant for improving the degumming efficiency in natural gas hydrate exploitation, improving the recovery efficiency of hydrates, and promoting the commercialization of hydrate solid fluidization exploitation.展开更多
Natural gas hydrates are widely distributed in marine and permafrost environments.As a novel energy resource,accurately describing reservoir characteristics and assessing energy potential is crucial for its commercial...Natural gas hydrates are widely distributed in marine and permafrost environments.As a novel energy resource,accurately describing reservoir characteristics and assessing energy potential is crucial for its commercial development.Resistivity logging serves as a valuable approach for achieving these goals.Nevertheless,due to inadequate comprehension of the electrical conductivity mechanism in hydrate-bearing sediments,existing data processing models still encounter certain challenges.This study conducts both core-scale and pore-scale simulation experiments to examine the relationship between resistivity variations and the distribution of gas hydrate porosity.The results indicate that the characteristics of resistivity variation is associated with the gas hydrate formation process,and the gas hydrate saturation index,denoted as‘n',varies between 0 and 3 depending on different gas hydrate distribution patterns.As the saturation increases,gas hydrate distribution in pore spaces transitions from floating to contacting and cementing patterns.It is proposed that the aqueous pore tortuosity can be utilized to correct the saturation index‘n'in Archie's equation.Based on the analysis of experimental data,a correction method for Archie's equation is suggested,and its effectiveness in controlling relative error has been validated.展开更多
The National Gas Hydrate Program expeditions(NGHP-01 and-02)have conclusively proven the presence of hydrate deposits on the eastern coast of India.The novelty of the present study lies in its investigation of the ric...The National Gas Hydrate Program expeditions(NGHP-01 and-02)have conclusively proven the presence of hydrate deposits on the eastern coast of India.The novelty of the present study lies in its investigation of the richest gas hydrate deposit(hydrate saturation[Sh]>0.75),NGHP-01-10D,in the Krishna-Godavari(KG)Basin,India.The study presents a first look at the long-term gas production viability using a single vertical well,subjected to variations in production interval and bottom hole pressure.Specifically,we compared the gas production at bottom hole pressures of 3-6 MPa and production intervals of 20-40 m.The results indicate production rates that are technically feasible but lower than commercially acceptable standards.Increasing the bottom hole pressure drawdown from 6 MPa to 3 MPa increased the gas production from 1297 m^(3)/d to 4902 m^(3)/d(i.e.,more than tripling the average daily gas production).Meanwhile,while expanding the production interval from 20 m to 40 m led to an increase in gas production,it also resulted in higher water production.As a result,the average gas-to-water ratio(RGW)decreased from 9.5 to 5.3 with the expansion of the production interval,thereby highlighting the need to optimize the interval length.Furthermore,the spatial evolution of certain thermodynamic parameters,including pressure,temperature,and phase saturation(methane,water,and hydrate),underscores the critical role of heat transfer from the UB.Our study findings offer valuable insights for long-term production forecasting,the delineation of phase evolution patterns,and the identification of potential flow barriers that may impede deliverability.展开更多
With the development of offshore oil and gas resources,hydrates pose a significant challenge to flow assurance.Hydrates can form,accumulate,and settle in pipelines,causing blockages,reducing transport capacity,and lea...With the development of offshore oil and gas resources,hydrates pose a significant challenge to flow assurance.Hydrates can form,accumulate,and settle in pipelines,causing blockages,reducing transport capacity,and leading to significant economic losses and fatalities.As oil and gas exploration moves deeper into the ocean,the issue of hydrate blockages has become more severe.It is essential to take adequate measures promptly to mitigate the hazards of hydrate blockages after they form.However,a prerequisite for effective mitigation is accurately detecting the location and amount of hydrate formation.This article summarizes the temperature–pressure,acoustic,electrical,instrumental–response,and flow characteristics of hydrate formation and blocking under various conditions.It also analyzes the principles,limitations,and applicability of various blockage detection methods,including acoustic,transient,and fiber-optic-based methods.Finally,it lists the results of field experiments and commercially used products.Given their advantages of accuracy and a wide detection range,acoustic pulse reflectometry and transient-based methods are considered effective for detecting hydrate blockages in future underwater pipelines.Using strict backpressure warnings combined with accurate detection via acoustic pulse reflectometry or transient-based methods,efficient and timely diagnosis of hydrate blockages can be achieved.The use of a hydrate model combined with fiber optics could prove to be an effective method for detecting blockages in newly laid pipelines in the future.展开更多
The Shenhu Area in the South China Sea is rich in oil and gas resources and has many vertical gas chimneys,making it an excellent geological environment for hydrate accumulation.This paper examines the geological cond...The Shenhu Area in the South China Sea is rich in oil and gas resources and has many vertical gas chimneys,making it an excellent geological environment for hydrate accumulation.This paper examines the geological conditions governing these gas-chimneys.A numerical simulation method based on the partial-equilibrium reaction model of hydrate was applied to simulate the migration of methane gas and the resultant hydrate formation when the gas enters the hydrate stability zone under the seabed through gas-chimneys.The dynamics of this gaschimney hydrate accumulation were analyzed,and the influences of different factors―namely,the fluid supply time,rate,and temperature―on the formation temperature and ultimate distribution of the hydrate reservoir were evaluated.The simulation results indicate that the accumulation of hydrate via gas-chimneys is significantly affected by the temperature of the gas source,the transfer state of the methane gas,and the number of cycles of alternating gas-water invasion.Hydrate accumulation takes shape in an annular or semi-annular distribution pattern divided by fluid state as follows:a two-phase gas-water zone,a three-phase gas-water-hydrate zone,a two-phase water-hydrate zone,and a phase of water passing from the inside to the outside.Formation inclination and reservoir heterogeneity can greatly affect the distribution shape and abundance of the hydrate.A high fluid supply temperature,frequent alternating invasions of gas and water,and long-term pore-water invasion at a high rate can jointly cause a large central hydrate-free zone.In contrast,a long-term supply shutdown during the alternating gas-water invasion process,and a high gas rate with a low water rate in the gas-dominant invasion stage,foster the accumulation of hydrate in great abundance and with considerable thickness.The results of this study can help us understand the accumulation of hydrate through gas chimneys in the Shenhu Area.展开更多
Molecular dynamics simulations were performed to study the microscopic working mechanism of fast hydrate formation from active ice.We successfully simulated the cyclic process of ice melt-hydrate formation-ice melt.Th...Molecular dynamics simulations were performed to study the microscopic working mechanism of fast hydrate formation from active ice.We successfully simulated the cyclic process of ice melt-hydrate formation-ice melt.The simulation results showed that active ice could significantly accelerate the formation of hydrates and exhibit high gas sto rage capacity.The oxygen atoms of the sulfate group in SDS formed hydrogen bonds with the hydrogen atoms of water molecules in the ice,destroying the orderly arranged structures of the ice surface.SDS also acted as a promoter to accelerate the mass transfer of vips in the liquid phase,thereby promoting the nucleation and growth of hydrates.The ordered structures of liquid phase formed by ice melting and the formation of cage-like structures facilitated by ice surface defects were beneficial to the nucleation and growth of hydrates.The formation of the hydrate shell accelerated the migration of the vips from the gas phase to the liquid phase.As the ice continued to melt,sufficient vips and water molecules ensured the stable growth of hydrates.展开更多
Natural gas hydrates are crystalline solid complexes with different morphologies found in marine sediments and permafrost zones. The petrophysical properties of gas hydrate-bearing sediments(GHBS) are crucial for unde...Natural gas hydrates are crystalline solid complexes with different morphologies found in marine sediments and permafrost zones. The petrophysical properties of gas hydrate-bearing sediments(GHBS) are crucial for understanding the characteristics of gas hydrate reservoirs, the spatial distribution of natural gas hydrates, and their exploitation potential. Geophysical exploration remains the primary approach for investigating the petrophysical properties of GHBS. However, limitations in resolution make it challenging to accurately characterize complex sediment structures, leading to difficulties in precisely interpreting petrophysical properties. Laboratory-based petrophysical experiments provide highly accurate results for petrophysical properties. Despite their accuracy, these experiments are costly, and difficulties in controlling variables may introduce uncertainties into geophysical exploration models.Advances in imaging and simulation techniques have established digital rock technology as an indispensable tool for enhancing petrophysical experimentation. This technology offers a novel microscopic perspective for elucidating the three-dimensional(3D) spatial distribution and multi-physical responses of GHBS. This paper presents an in-depth discussion of digital rock technology as applied to GHBS, with an emphasis on digital rock reconstruction and simulation of petrophysical properties. First, we summarize two common methods for constructing digital rocks of GHBS: petrophysical experimental methods and numerical reconstruction methods, followed by analyses of their respective advantages and limitations. Next, we delve into numerical simulation methods for evaluating GHBS petrophysical properties, including electrical, elastic, and fluid flow characteristics. Finally, we conduct a comprehensive analysis of the current trends in digital rock reconstruction and petrophysical simulation techniques for GHBS, emphasizing the necessity of multi-scale, multi-component, high-resolution 3D digital rock models to facilitate the precise characterization of complex gas hydrate reservoirs. Future applications of microscopic digital rock technology should be integrated with macroscopic geophysical exploration to enable more comprehensive and precise analyses of GHBS petrophysical properties.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.51939011)the Science and Technology Program of CNOOC Research Institute(Grant No.2023OTKK03)supported by the program of the Youth Innovation Promotion Association,Chinese Academy of Sciences(Grant No.2020326).
文摘Shear strength of hydrate-bearing sediment is an essential parameter for assessing landslide potential ofhydrate reservoirs under exploration conditions. However, the characteristics and simulation of thisshear strength under varying dissociation conditions have not been thoroughly investigated. To this end,a series of triaxial compression tests were first carried out on sediments with varying initial hydratesaturations along dissociation pathways. Combining measured data with microscale analysis, the underlyingmechanism for the evolution of shear strength in hydrate-bearing sediment was studied undervarying partial dissociation pathways. Moreover, a shear strength model for hydrate-bearing sedimentwas proposed, taking into account the hydrate saturation and the unhydrated water content. Apart fromthe parameters derived from the hydrate characteristic curve, only one additional model parameter isrequired. The proposed model was validated using measured data on hydrate sediments. The resultsindicate that the proposed model can effectively capture the shear strength behavior of hydrate-bearingsediment under varying dissociation paths. Finally, a sensitivity analysis of the model parameters wasconducted to characterize the proposed model.
基金This work was supported by the projects of the China Geological Survey(DD 20221703).
文摘Natural gas hydrate is a clean energy source with substantial resource potential.In contrast to conventional oil and gas,natural gas hydrate exists as a multi-phase system consisting of solids,liquids,and gases,which presents unique challenges and complicates the mechanisms of seepage and exploitation.Both domestic and international natural gas hydrate production tests typically employ a single-well production model.Although this approach has seen some success,it continues to be hindered by low production rates and short production cycles.Therefore,there is an urgent need to explore a new well network to significantly increase the production of a single well.This paper provides a comprehensive review of the latest advancements in natural gas hydrate research,including both laboratory studies and field tests.It further examines the gas production processes and development outcomes for single wells,dual wells,multi-branch wells,and multi-well systems under conditions of depressurization,thermal injection,and CO_(2) replacement.On this basis,well types and well networks suitable for commercial exploitation of natural gas hydrate were explored,and the technical direction of natural gas hydrate development was proposed.The study shows that fully exploiting the flexibility of complex structural wells and designing a well network compatible with the reservoir is the key to improving production from a single well.Moreover,multi-well joint exploitation is identified as an effective strategy for achieving large-scale,efficient development of natural gas hydrate.
基金supported by the Natural Science Starting Project of Sichuan Provincial Youth Foundation Project(2025ZNSFSC1356)Southwest Petroleum University,China(2023QHZ019)+1 种基金General Project of the Sichuan Provincial Natural Science Foundation,China(24NSFSC1295)Open fund of Dazhou Industrial Technology Institute of Intelligent Manufacturing,China(ZNZZ2215).
文摘During the production of natural gas hydrates,micron-sized sand particles coexist with hydrate within the transportation pipeline,posing a significant threat to the safety of pipeline flow.However,the influence of sand particles on hydrate formation mechanisms and rheological properties remains poorly understood.Consequently,using a high-pressure reactor system,the phase equilibrium conditions,hydrate formation characteristics,hydrate concentration,and the slurry viscosity in micron-sized sand system are investigated in this work.Furthermore,the effects of sand particle size,sand concentration,and initial pressure on these properties are analyzed.The results indicate that a high concentration of micron-sized sand particles enhances the formation of methane hydrates.When the volume fraction of sand particles exceeds or equals 3%,the phase equilibrium conditions of the methane hydrate shift to the left relative to that of the pure water system(lower temperature,higher pressure).This shift becomes more pronounced with smaller particle sizes.Besides,under these sand concentration conditions,methane hydrates exhibit secondary or even multiple formation events,though the formation rate decreases.Additionally,the torque increases significantly and fluctuates considerably.The Roscoe-Brinkman model yields the most accurate slurry viscosity calculations,and as sand concentration increases,both hydrate concentration and slurry viscosity also increase.
基金financial support received from the National Natural Science Foundation of China(Nos.51991364,and 42202347)。
文摘The commercial exploitation of natural gas hydrates is currently facing several challenges,including low production rates,limited recovery areas,and brief periods of continuous production.To address these issues,we propose a novel dual-enhanced stimulation(DES)method for marine hydrate reservoirs.This method involves injecting a special slurry that solidifies into porous,high-permeability,and highstrength slurry veins.These veins not only enhance permeability,allowing for faster gas and water flow,but also improve reservoir stability.This study experimentally investigated the split grouting of clayey-silty sediments with dual-enhanced slurry to assess the feasibility of DES and to explo re the slurry diffusion mechanism and micro-pore structure of the veins.The results showed that split grouting with dual-enhanced slurry exhibited frequent fracture initiation with quick pressure spikes and sharp declines,suggesting shorter fractures in clayey-silty sediments.As vertical stress increased,the primary diffusion direction of the dual-enhanced slurry shifted from horizontal to vertical,aligning with fracture propagation patterns observed during fracturing.Unlike hydraulic fracturing in hard rocks,split grouting in clayey-silty sediments encountered more difficult conditions.These veins formed through a recurring cycle of splitting into fractures and filling with slurry,occurring more frequently in weaker sediments with slower injection rates and higher vertical stress.Increased vertical stress hindered slurry vein diffu sion,easily resulting in compaction grouting near the grouting pipe.Additionally,three-dimensional laser scanning of the veins showed that those formed through split grouting were continuous and stable,with their thickness decreasing as diffusion distance increased.The morphology of these veins was shaped by factors such as grouting rate,formation stress,and elastic modulus,with higher rates and elastic moduli facilitating the formation of complex vein networks.Mercury intrusion porosimetry demonstrated that the DES method resulted in veins with consistent effective porosity between 65%and70%and median pore sizes of 11-15μm across different locations.These veins formed a well-connected porous network of smaller pores,significantly enhancing both permeability and sand control.The research findings validate the effectiveness of the DES method for marine hydrate reservoirs,providing a strategy for the safe and efficient exploitation of NGH resources.
基金supported by the Guangdong Basic and Applied Basic Research Foundation(Grant No.2022A1515110376)the Open Research Fund of National Center for International Research on Deep Earth Drilling and Resource Development,Ministry of Science and Technology(Grant No.DEDRD-2023-04)the Fundamental Research Funds for the Central Universities,China University of Geosciences(Grant No.107-G1323523046).
文摘The flow behaviors of gas and water in hydrate-bearing sediments(HBS)are significantly affected by the threshold pressure gradient(TPG).During long-term natural gas hydrates(NGHs)mining,there exists creep deformation in HBS,which significantly alters pore structures,makes the flow path of fluid more complex,and leads to changes in TPG.Thus,clarifying the evolution of TPG in HBS during creep is essential for NGH production,but it also confronts enormous challenges.In this study,based on the nonlinear creep constitutive model,a novel theoretical TPG model of HBS during creep is proposed that considers pore structures and hydrate pore morphology.The established model is validated against experimental data,demonstrating its ability to capture the evolution of TPG and permeability in HBS during creep.Additionally,the relationship between initial hydrate saturation and TPG of HBS during creep is revealed by sensitivity analysis.The creep strain increases with the decrease in initial hydrate saturation,leading to a greater TPG and a lower permeability.The evolution of TPG at the stable creep stage and the accelerated creep stage is primarily controlled by the Kelvin element and visco-plastic element,respectively.This novel proposed model provides a mechanistic understanding of TPG evolution in HBS during creep,and it is of great significance to optimize the exploitation of NGHs.
基金supported by National Natural Science Foundation of China(22278424,22127812,22008257).
文摘As a kind of novel environmental-friendly surfactant,Gemini surfactant has attracted extensive research interests in its effects on gas hydrate formation.We investigated the effects of dioctyl sodium sulfosuccinate(AOT)on the formation thermodynamics/kinetics of CH_(4)and CO_(2)hydrates.Experimental results indicate that while AOT does not exhibit significant thermodynamic promotion for hydrate formation,it demonstrates favorable kinetic promotion effects.Its promotion effect surpasses that of the traditional kinetic promoter SDS and can enhance the gas storage capacity of hydrates.Utilizing the Chen-Guo hydrate model and adsorption kinetic model,we established a kinetic model for AOT with a predictive deviation of 7.17%and fitted key parameters accordingly.
基金financially supported by the National Key Research and Development Plan(2023YFC2811001)the National Natural Science Foundation of China(42206233)the Taishan Scholars Program(tsqn202312280,tsqn202306297)。
文摘Hydraulic fracturing technology has played an important role in the exploitation of unconventional oil and gas resources,however,its application to gas hydrate reservoirs has been rarely studied.Currently,there is still limited understanding of the propagation and extension of fractures around the wellbore during the fracturing process of horizontal wells in hydrate reservoirs,as well as the stress interference patterns between fractures.This study simulates hydraulic fracturing processes in hydrate reservoirs using a fluidsolid coupling discrete element method(DEM),and analyzes the impacts of hydrate saturation and geological and engineering factors on fracture extension and stress disturbance.The results show that hydraulic fracturing is more effective when hydrate saturation exceeds 30%and that fracture pressure increases with saturation.The increase in horizontal stress differential enhances the directionality of fracture propagation and reduces stress disturbance.The distribution uniformity index(DUI)reveals that injection pressure is directly proportional to the number of main fractures and inversely proportional to fracturing time,with fracturing efficiency depending on the spacing between injection points and the distance between wells.This work may provide reference for the commercial exploitation of natural gas hydrates.
基金supported by the Key Research Program of the Institute of Geology&Geophysics,CAS(Grant No.IGGCAS-201903).
文摘Natural gas hydrates widely accumulate in submarine sediments composed of clay minerals.However,due to the complex physiochemistry and micron-sized particles of clay minerals,their effects on methane hydrate(MH)formation and dissociation are still in controversy.In this study,montmorillonite and illite were separately mixed with quartz sand to investigate their effects on MH formation and dissociation.The microstructure of synthesized samples was observed by cryo-SEM innovatively to understand the effects of montmorillonite and illite on MH phase transition in micron scale.Results show that montmorillonite and illite both show the inhibition on MH formation kinetics and water-to-hydrate conversion,and illite shows a stronger inhibition.The 10 wt%montmorillonite addition significantly retards MH formation rate,and the 20 wt%montmorillonite has a less inhibition on the rate.The increase of illite mass ratio(0-20 wt%)retards the rate of MH formation.As the content of clay minerals increase,the water-to-hydrate conversion decreases.Cryo-SEM images presented that montmorillonite aggregates separate as individual clusters while illite particles pack as face-to-face configuration under the interaction with water.The surface-overlapped illite aggregates would make sediments pack tightly,hinder the contact between gas and water,and result in the more significant inhibition on MH formation kinetics.Under the depressurization method,the addition of clay minerals facilitates MH dissociation rate.Physicochemical properties of clay minerals and MH distribution in the pore space lead to the faster dissociation rate in clay-containing sediments.The results of this study would provide beneficial guides on geological investigations and optimizing strategies of natural gas production in marine hydrate-bearing sediments.
基金supported by the Gas Hydrate R&D Organization and the Korea Institute of Geoscience and Mineral Resources(KIGAM)(GP2021-010)supported by the National Research Foundation of Korea(NRF)grant funded by the Korean government(MSIT)(No.2021R1C1C1004460)Korea Institute of Energy Technology Evaluation and Planning(KETEP)grant funded by the Korean government(MOTIE)(20214000000500,Training Program of CCUS for Green Growth).
文摘Gas hydrate(GH)is an unconventional resource estimated at 1000-120,000 trillion m^(3)worldwide.Research on GH is ongoing to determine its geological and flow characteristics for commercial produc-tion.After two large-scale drilling expeditions to study the GH-bearing zone in the Ulleung Basin,the mineral composition of 488 sediment samples was analyzed using X-ray diffraction(XRD).Because the analysis is costly and dependent on experts,a machine learning model was developed to predict the mineral composition using XRD intensity profiles as input data.However,the model’s performance was limited because of improper preprocessing of the intensity profile.Because preprocessing was applied to each feature,the intensity trend was not preserved even though this factor is the most important when analyzing mineral composition.In this study,the profile was preprocessed for each sample using min-max scaling because relative intensity is critical for mineral analysis.For 49 test data among the 488 data,the convolutional neural network(CNN)model improved the average absolute error and coefficient of determination by 41%and 46%,respectively,than those of CNN model with feature-based pre-processing.This study confirms that combining preprocessing for each sample with CNN is the most efficient approach for analyzing XRD data.The developed model can be used for the compositional analysis of sediment samples from the Ulleung Basin and the Korea Plateau.In addition,the overall procedure can be applied to any XRD data of sediments worldwide.
基金supported by the Russian Science Foundation(23-29-00830).
文摘Morphology and growth rate of carbon dioxide hydrate on the interface between liquid carbon dioxide and humic acid solutions were studied in this work.It was found that after the growth of the hydrate film at the interface,further growth of hydrate due to the suction of water in the capillary system formed between the wall of the cuvette and the end boundary of the hydrate layer occurs.Most probably,substantial effects on the formation of this capillary system may be caused by variations in reactor wall properties,for example,hydrophobic-hydrophilic balance,roughness,etc.We found,that the rate of CO_(2) hydrate film growth on the surface of the humic acid aqueous solution is 4-fold to lower in comparison with the growth rate on the surface of pure water.We suppose that this is caused by the adsorption of humic acid associates on the surface of hydrate particles and,as a consequence,by the deceleration of the diffusion of dissolved carbon dioxide to the growing hydrate particle.
文摘An efficient acetic acid mediated metal-free oxidative C—H cross coupling of imidazo[1,2-a]pyridines with glyoxal hydrates has been developed under air atmosphere.The present protocol exhibits broad substrate scope,good functional group tolerance,and enables the construction of a series of 1,2-dicarbonyl imidazo[1,2-a]pyridines in good yields.The reaction mechanism studies suggest that the reactions proceed through the electrophilic substitution and subsequent oxidation pathway.
基金supported by the Sinopec Technology Research and Development Project(No.30000000-22-ZC0607-0235,No.33550000-22-ZC0607-0009)the National Natural Science Foundation of China(No.52334002).
文摘Natural gas hydrate widely exists in the South China Sea as clean energy.A three-phase transition layer widely exists in low permeability Class I hydrates in the Shenhu offshore area.Therefore,taking into account the low-permeability characteristics with an average permeability of 5.5 mD and moderate heterogeneity,a 3-D geological model of heterogeneous Class I hydrate reservoirs with three-phase transition layers is established by Kriging interpolation and stochastic modeling method,and a numerical simulation model is used to describe the depressurization production performance of the reservoir.With the development of depressurization,a specific range of complete decomposition zones appear both in the hydrate and transition layers.The entire decomposition zone of the whole reservoir tends to outward and upward diffusion.There is apparent methane escape in the three-phase transition layer.Due to the improvement of local permeability caused by the phase transition of hydrate dissociation,some methane accumulation occurs at the bottom of the hydrate layer,forming a local methane enrichment zone.The methane migration trends in reservoirs are mainly characterized by movement toward production wells and hydrate layers under the influence of gravity.However,due to the permeability limitation of hydrate reservoirs,many fluids have not been effectively produced and remain in the reservoir.Therefore,to improve the effective pressure drop of the reservoir,the perforation method and pressure reduction method were optimized by analyzing the influencing factors based on the gas production rate.The comparative study demonstrates that perforating through the free gas layer combined with one-time depressurization can enhance the effective depressurization and improve production performance.The gas production rate from perforating through the free gas layer can be twice as high as that from perforating through the transition layer.This study can provide theoretical support for the utilization of marine energy.
基金funded by the National Key Research and Development Program of China(grant number 2023YFC3009204)the National Natural Science Foundation of China(grant number 52174015).
文摘Field tests have demonstrated that depressurization with controlled sand production is an effective technique for natural gas hydrate extraction.Variations in depositional environments and processes result in significant heterogeneity within subsea natural gas hydrate-bearing sediments.However,the influence of permeability heterogeneity on production performance during depressurization with controlled sand production remains inadequately understood.In this study,a multiphase,multi-component mathematical model is developed to simulate depressurization with controlled sand production in methane hydrate-bearing sediments,incorporating geological conditions representative of unconsolidated argillaceous siltstone hydrate deposits in the Shenhu area of the South China Sea.The effects of permeability heterogeneity-specifically,horizontal autocorrelation length and global permeability heterogeneity-on production performance during depressurization with sand production are investigated using geostatistical modeling combined with finite difference method based numerical simulations.Results show that as the horizontal autocorrelation length of permeability distribution increases,cumulative gas production first rises and then declines,reaching its peak at λ_(Dh)=0.1,whereas sand production steadily increases.In addition,higher formation permeability heterogeneity results in increased cumulative gas and sand production,suggesting that greater heterogeneity promotesmethane hydrate decomposition and gas recovery.These findings can offer valuable insights for optimizing future field development of hydrate-bearing sediments by depressurization with controlled sand production.
基金funded by the State Key Laboratory of Natural Gas Hydrate of China(2022-KFJJ-SHW)the National Key Research and Development Program of China(2021YFC2800903)+2 种基金the National Natural Science Foundation of China(52004235)the National Natural Science Foundation General Program of China(52374011)the Miaozi Engineering Cultivation Project of Sichuan Science and Technology Department of China(MZG20230127).
文摘Weak cementation between natural gas hydrates and mud–sand seriously affects the solid-fluidized mining of natural gas hydrates. In this study, we analyze the debonding of natural gas hydrate sediment (NGHS) particles by applying the principle of spiral-cyclone coupling separation. To achieve this, weakly cemented NGHS particle and mechanical models were established. In the flow field of the spiral-cyclone flow-coupling separator, the motion characteristics of the weakly cemented NGHS particles and the destruction process of the cementation bond were analyzed. The destruction of the bonds mainly occurred in the spiral channel, and the destruction efficiency of the bonds was mainly affected by the rotational speed. Collision analysis of the particles and walls showed that when the velocity is 10–16 m·s^(−1), the cementation bond can be broken. The greater the speed, the better the effect of the bond fracture. The breaking rate of the cementation bonds was 85.7%. This study is significant for improving the degumming efficiency in natural gas hydrate exploitation, improving the recovery efficiency of hydrates, and promoting the commercialization of hydrate solid fluidization exploitation.
基金financially supported by the National Natural Science Foundation of China(No.42376067)the Natural Science Foundation of Shandong Province(No.ZR202011030013)+1 种基金the Laoshan Laboratory(No.LSKJ202203506)the China Geological Survey Program(No.DD20230064)。
文摘Natural gas hydrates are widely distributed in marine and permafrost environments.As a novel energy resource,accurately describing reservoir characteristics and assessing energy potential is crucial for its commercial development.Resistivity logging serves as a valuable approach for achieving these goals.Nevertheless,due to inadequate comprehension of the electrical conductivity mechanism in hydrate-bearing sediments,existing data processing models still encounter certain challenges.This study conducts both core-scale and pore-scale simulation experiments to examine the relationship between resistivity variations and the distribution of gas hydrate porosity.The results indicate that the characteristics of resistivity variation is associated with the gas hydrate formation process,and the gas hydrate saturation index,denoted as‘n',varies between 0 and 3 depending on different gas hydrate distribution patterns.As the saturation increases,gas hydrate distribution in pore spaces transitions from floating to contacting and cementing patterns.It is proposed that the aqueous pore tortuosity can be utilized to correct the saturation index‘n'in Archie's equation.Based on the analysis of experimental data,a correction method for Archie's equation is suggested,and its effectiveness in controlling relative error has been validated.
文摘The National Gas Hydrate Program expeditions(NGHP-01 and-02)have conclusively proven the presence of hydrate deposits on the eastern coast of India.The novelty of the present study lies in its investigation of the richest gas hydrate deposit(hydrate saturation[Sh]>0.75),NGHP-01-10D,in the Krishna-Godavari(KG)Basin,India.The study presents a first look at the long-term gas production viability using a single vertical well,subjected to variations in production interval and bottom hole pressure.Specifically,we compared the gas production at bottom hole pressures of 3-6 MPa and production intervals of 20-40 m.The results indicate production rates that are technically feasible but lower than commercially acceptable standards.Increasing the bottom hole pressure drawdown from 6 MPa to 3 MPa increased the gas production from 1297 m^(3)/d to 4902 m^(3)/d(i.e.,more than tripling the average daily gas production).Meanwhile,while expanding the production interval from 20 m to 40 m led to an increase in gas production,it also resulted in higher water production.As a result,the average gas-to-water ratio(RGW)decreased from 9.5 to 5.3 with the expansion of the production interval,thereby highlighting the need to optimize the interval length.Furthermore,the spatial evolution of certain thermodynamic parameters,including pressure,temperature,and phase saturation(methane,water,and hydrate),underscores the critical role of heat transfer from the UB.Our study findings offer valuable insights for long-term production forecasting,the delineation of phase evolution patterns,and the identification of potential flow barriers that may impede deliverability.
基金supported by the National Natural Science Foundation of China(52476058,U21B2065,52006024,and 52306188)the National Key Research and Development(2022YFC2806200).
文摘With the development of offshore oil and gas resources,hydrates pose a significant challenge to flow assurance.Hydrates can form,accumulate,and settle in pipelines,causing blockages,reducing transport capacity,and leading to significant economic losses and fatalities.As oil and gas exploration moves deeper into the ocean,the issue of hydrate blockages has become more severe.It is essential to take adequate measures promptly to mitigate the hazards of hydrate blockages after they form.However,a prerequisite for effective mitigation is accurately detecting the location and amount of hydrate formation.This article summarizes the temperature–pressure,acoustic,electrical,instrumental–response,and flow characteristics of hydrate formation and blocking under various conditions.It also analyzes the principles,limitations,and applicability of various blockage detection methods,including acoustic,transient,and fiber-optic-based methods.Finally,it lists the results of field experiments and commercially used products.Given their advantages of accuracy and a wide detection range,acoustic pulse reflectometry and transient-based methods are considered effective for detecting hydrate blockages in future underwater pipelines.Using strict backpressure warnings combined with accurate detection via acoustic pulse reflectometry or transient-based methods,efficient and timely diagnosis of hydrate blockages can be achieved.The use of a hydrate model combined with fiber optics could prove to be an effective method for detecting blockages in newly laid pipelines in the future.
基金supported by the Guangzhou Marine Geological Survey,China Geological Survey,Guangzhou,China(No.2022C-24-216)financed by the General Project of the Shandong Natural Science Foundation,China(No.ZR2020ME090).
文摘The Shenhu Area in the South China Sea is rich in oil and gas resources and has many vertical gas chimneys,making it an excellent geological environment for hydrate accumulation.This paper examines the geological conditions governing these gas-chimneys.A numerical simulation method based on the partial-equilibrium reaction model of hydrate was applied to simulate the migration of methane gas and the resultant hydrate formation when the gas enters the hydrate stability zone under the seabed through gas-chimneys.The dynamics of this gaschimney hydrate accumulation were analyzed,and the influences of different factors―namely,the fluid supply time,rate,and temperature―on the formation temperature and ultimate distribution of the hydrate reservoir were evaluated.The simulation results indicate that the accumulation of hydrate via gas-chimneys is significantly affected by the temperature of the gas source,the transfer state of the methane gas,and the number of cycles of alternating gas-water invasion.Hydrate accumulation takes shape in an annular or semi-annular distribution pattern divided by fluid state as follows:a two-phase gas-water zone,a three-phase gas-water-hydrate zone,a two-phase water-hydrate zone,and a phase of water passing from the inside to the outside.Formation inclination and reservoir heterogeneity can greatly affect the distribution shape and abundance of the hydrate.A high fluid supply temperature,frequent alternating invasions of gas and water,and long-term pore-water invasion at a high rate can jointly cause a large central hydrate-free zone.In contrast,a long-term supply shutdown during the alternating gas-water invasion process,and a high gas rate with a low water rate in the gas-dominant invasion stage,foster the accumulation of hydrate in great abundance and with considerable thickness.The results of this study can help us understand the accumulation of hydrate through gas chimneys in the Shenhu Area.
基金National Natural Science Foundation of China(22178378,22127812 and 22468054)“Tianchi Talent”Recruitment Program,Xinjiang Tianshan Innovation Team(2022TSYCTD0002)Xinjiang Uygur Region“One Case,One Policy”Strategic Talent Introduction Project(XQZX20240054)。
文摘Molecular dynamics simulations were performed to study the microscopic working mechanism of fast hydrate formation from active ice.We successfully simulated the cyclic process of ice melt-hydrate formation-ice melt.The simulation results showed that active ice could significantly accelerate the formation of hydrates and exhibit high gas sto rage capacity.The oxygen atoms of the sulfate group in SDS formed hydrogen bonds with the hydrogen atoms of water molecules in the ice,destroying the orderly arranged structures of the ice surface.SDS also acted as a promoter to accelerate the mass transfer of vips in the liquid phase,thereby promoting the nucleation and growth of hydrates.The ordered structures of liquid phase formed by ice melting and the formation of cage-like structures facilitated by ice surface defects were beneficial to the nucleation and growth of hydrates.The formation of the hydrate shell accelerated the migration of the vips from the gas phase to the liquid phase.As the ice continued to melt,sufficient vips and water molecules ensured the stable growth of hydrates.
基金the National Key R&D Program of China(2023YEE0119900)National Natural Science Foundation of China(Nos.92058211,42204105 and 42121005)+4 种基金Fundamental Research Funds for the Central Universities(No.862201013140)111 project(No.B20048)the International(Regional)Cooperation and Exchange Programs(No.12411530092)the Young Talent Fund of Association for Science and Technology in Shaanxi(No.20230703)Technology Innovation Leading Program of Shaanxi(No.2024 ZC-YYDP-27).
文摘Natural gas hydrates are crystalline solid complexes with different morphologies found in marine sediments and permafrost zones. The petrophysical properties of gas hydrate-bearing sediments(GHBS) are crucial for understanding the characteristics of gas hydrate reservoirs, the spatial distribution of natural gas hydrates, and their exploitation potential. Geophysical exploration remains the primary approach for investigating the petrophysical properties of GHBS. However, limitations in resolution make it challenging to accurately characterize complex sediment structures, leading to difficulties in precisely interpreting petrophysical properties. Laboratory-based petrophysical experiments provide highly accurate results for petrophysical properties. Despite their accuracy, these experiments are costly, and difficulties in controlling variables may introduce uncertainties into geophysical exploration models.Advances in imaging and simulation techniques have established digital rock technology as an indispensable tool for enhancing petrophysical experimentation. This technology offers a novel microscopic perspective for elucidating the three-dimensional(3D) spatial distribution and multi-physical responses of GHBS. This paper presents an in-depth discussion of digital rock technology as applied to GHBS, with an emphasis on digital rock reconstruction and simulation of petrophysical properties. First, we summarize two common methods for constructing digital rocks of GHBS: petrophysical experimental methods and numerical reconstruction methods, followed by analyses of their respective advantages and limitations. Next, we delve into numerical simulation methods for evaluating GHBS petrophysical properties, including electrical, elastic, and fluid flow characteristics. Finally, we conduct a comprehensive analysis of the current trends in digital rock reconstruction and petrophysical simulation techniques for GHBS, emphasizing the necessity of multi-scale, multi-component, high-resolution 3D digital rock models to facilitate the precise characterization of complex gas hydrate reservoirs. Future applications of microscopic digital rock technology should be integrated with macroscopic geophysical exploration to enable more comprehensive and precise analyses of GHBS petrophysical properties.
