It has been evidenced that shallow gas hydrate resources are abundant in deep oceans worldwide.Their geological back-ground,occurrence,and other characteristics differ significantly from deep-seated hydrates.Because o...It has been evidenced that shallow gas hydrate resources are abundant in deep oceans worldwide.Their geological back-ground,occurrence,and other characteristics differ significantly from deep-seated hydrates.Because of the high risk of well construction and low production efficiency,they are difficult to be recovered by using conventional oil production methods.As a result,this paper proposes an alternative design based on a combination of radial drilling,heat injection,and backfilling methods.Multi-branch holes are used to penetrate shallow gas hydrate reservoirs to expand the depressurization area,and heat injection is utilized as a supplement to improve gas production.Geotechnical information collected from an investigation site close to the offshore production well in the South China Sea is used to assess the essential components of this plan,including well construction stability and gas production behavior.It demonstrates that the hydraulic fracturing of the 60mbsf overburden layer can be prevented by regulating the drilling fluid densities.However,the traditional well structure is unstable,and the suction anchor is advised for better mechanical performance.The gas produc-tion rate can be significantly increased by combining hot water injection and depressurization methods.Additionally,the suitable produc-tion equipment already in use is discussed.展开更多
Gas hydrate technology has considerable potential in many fields.However,due to the lack of understanding of the micro mechanism of hydrate formation,it has not been commercially applied so far.Gas hydrate formation i...Gas hydrate technology has considerable potential in many fields.However,due to the lack of understanding of the micro mechanism of hydrate formation,it has not been commercially applied so far.Gas hydrate formation is essentially a gas-liquid-solid phase transition of water and gas molecules at a certain temperature and pressure.The key to the hydrate formation is the transformation of water molecule from disordered arrangement to ordered arrangement.In this process,weakly hydrogen bonded water will be correspondingly converted to strongly hydrogen bonded water.Through in situ Raman analysis and experiments,the position change of the corresponding peaks of the strongly hydrogen bonded water and the weakly hydrogen bonded water was compared in this work,and the key microscopic process and influence of gas hydrate formation in different systems were comprehensively studied and summarized.It is found that,with the decrease of temperature,the OAH of the weakly hydrogen bonded water remains unchanged when the temperature drops to a certain value,which is the key to the transformation of water into cage hydrate rather than ice.The conversion from the weakly hydrogen bonded water to the strongly hydrogen bonded water is closely related to the gas-liquid interface force,the hydrophilicity/hydrophobicity of the promoter,the ionization degree of liquid,and the electrostatic field of the system.Among the four most common promoters,tetrahydrofuran(THF)has the highest efficiency in promoting methane(CH4)hydrate formation.Therefore,this study provides a scientific direction and basis for the development of high efficient hydrate formation promoters,which can effectively weaken the hydrogen bond of weakly hydrogen bonded water and promote the conversion of weakly hydrogen bonded water to strongly hydrogen bonded water.展开更多
The changes in the mechanical properties of gas hydrate-bearing sediments(GHBS) induced by gas hydrate(GH) dissociation are essential to the evaluation of GH exploration and stratum instabilities. Previous studies pre...The changes in the mechanical properties of gas hydrate-bearing sediments(GHBS) induced by gas hydrate(GH) dissociation are essential to the evaluation of GH exploration and stratum instabilities. Previous studies present substantial mechanical data and constitutive models for GHBS at a given GH saturation under the non-dissociated condition. In this paper, GHBS was formed by the gas saturated method, GH was dissociated by depressurization until the GH saturation reached different dissociation degrees. The stress–strain curves were measured using triaxial tests at a same pore gas pressure and different confining pressures. The results show that the shear strength decreases progressively by 30%–90% of the initial value with GH dissociation, and the modulus decreases by 50% –75%. Simplified relationships for the modulus, cohesion, and internal friction angle with GH dissociated saturation were presented.展开更多
Study of the surface morphology of gas hydrate is of great importance in understanding its physical properties and occurrence.In order to investigate the surface morphology of different types(sI and sII)and occurrence...Study of the surface morphology of gas hydrate is of great importance in understanding its physical properties and occurrence.In order to investigate the surface morphology of different types(sI and sII)and occurrences(pore-filling and fracture-filling)of gas hydrate,both lab-synthesized and drilled-gas hydrate samples were measured using cryo-scanning electron microscopy(cryo-SEM).Results showed that the surface of s I hydrate was relatively smooth,and spongy nano-pores(200–400 nm)gradually occurred at the surface during continuous observation.The surface of sII hydrate was more compact,showing a tier-like structure.Hydrate occurred in quartz sand and usually filled the pores of the sediments and both hydrate and sediments were cemented with each other.SEM observation of the gas hydrates collected from the South China Sea showed that the surface morphology and contact relation with sediments varied with hydrate occurrence.For instance,hydrates dispersed in sediments mainly filled the pores of the sediments.The existence of microorganism shells,such as foraminifera,was beneficial to the formation of gas hydrate.When hydrate occurred as a massive or vein structure,it was easily distinguished from the surrounding sediments.The surface of hydrate with massive or vein structure showed two distinct characters:one was dense and smooth,the other is porous(several to tens of micrometers in diameter).The occurrence of different hydrate morphologies was probably caused by the supplement rates of methane gas.展开更多
Natural gas hydrates easily form in pipelines,causing potential safety issues during oil and gas production and transportation.Injecting gas hydrate inhibitors is one of the most effective methods for preventing gas h...Natural gas hydrates easily form in pipelines,causing potential safety issues during oil and gas production and transportation.Injecting gas hydrate inhibitors is one of the most effective methods for preventing gas hydrate formation or aggregation.However,some thermodynamic hydrate inhibitors are toxic and harmful to the environment,whereas degradation of kinetic inhibitors is difficult.Therefore,environmentally friendly and easily biodegradable novel green inhibitors have been proposed and investigated.This paper provides a short but systematic review of the inhibitory performance of amino acids,antifreeze proteins,and ionic liquids.For different hydrate formation systems,the influences of the inhibitor type,structure,and concentration on the inhibitory effects are summarized.The mechanism of green inhibitors as kinetic inhibitors is also discussed.The progress described here will facilitate further developments of such green inhibitors for gas hydrate formation.展开更多
Gas leakage is an important consideration in natural systems that experience gas hydrate accumulation.A number of velocity models have been created to study hydrate-bearing sediments,including the BGTL theory,the weig...Gas leakage is an important consideration in natural systems that experience gas hydrate accumulation.A number of velocity models have been created to study hydrate-bearing sediments,including the BGTL theory,the weighted equation,the Wood equation,the K-T equation,and the effective medium theory.In previous work,we regarded water as the pore fluid,which meant its density and bulk modulus values were those of water.This approach ignores the presence of gas,which results in a biased calculation of the pore fluid's bulk modulus and density.To take into account the effect of gas on the elastic wave velocity,it is necessary to recalculate the bulk modulus and density of an equivalent medium.Thus,a high-pressure reactor device for simulating leakage systems was developed to establish the relationship between wave velocity and hydrate saturation in methane-flux mode.A comparison of the values calculated by the velocity model with the experimental data obtained in this study indicates that the effective medium theory(EMT,which considers gas effects)is more applicable than other models.For hydrate saturations of 10%–30%,the result ranges between EMT-B(homogenous gas distribution)and EMT-B(patchy gas distribution).For hydrate saturations of 30%–60%,the results are similar to those of the EMT-B(homogenous gas distribution)mode,whereas hydrate saturations of 60%–70%yield results similar to those of the EMT-A mode.For hydrate saturations greater than 80%,the experimental results are similar to those of the EMT-B mode.These results have significance for hydrate exploitation in the South China Sea.展开更多
The safe and efficient development of natural gas hydrate requires a deep understanding of the deformation behaviors of reservoirs.In this study,a series of triaxial shearing tests are carried out to investigate the d...The safe and efficient development of natural gas hydrate requires a deep understanding of the deformation behaviors of reservoirs.In this study,a series of triaxial shearing tests are carried out to investigate the deformation properties of hydrate-bearing sediments.Variations of volumetric and lateral strains versus hydrate saturation are analyzed comprehensively.Results indicate that the sediments with high hydrate saturation show dilative behaviors,which lead to strain-softening characteristics during shearing.The volumetric strain curves have a tendency to transform gradually from dilatation to compression with the increase in effective confining pressure.An easy prediction model is proposed to describe the relationship between volumetric and axial strains.The model coefficientβis the key dominating factor for the shape of volumetric strain curves and can be determined by the hydrate saturation and stress state.Moreover,a modified model is established for the calculation of lateral strain.The corresponding determination method is provided for the easy estimation of model coefficients for medium sand sediments containing hydrate.This study provides a theoretical and experimental reference for deformation estimation in natural gas hydrate development.展开更多
Mechanical properties of hydrate-bearing fine-grained sediments are crucial to effectively mitigate environmental risks caused by artificial and natural decomposition of natural gas hydrates,and the decomposition can ...Mechanical properties of hydrate-bearing fine-grained sediments are crucial to effectively mitigate environmental risks caused by artificial and natural decomposition of natural gas hydrates,and the decomposition can induce laterally confined deformation.To explore the effect of natural gas hydrates on laterally confined compression properties,consolidation tests are conducted on remolded hydrate-free and hydrate-bearing samples by using natural fine-grained sediments collected from the northern South China Sea as the host sediments,and empirical equations are developed based on the analyses of consolidation characteristics.The results show that vertical loading induces a reduction in void ratio,and the reduction increases with decreasing hydrate saturation when samples are subjected to the same vertical stress change.The compression index of samples is about 0.53 whether there is hydrate or not,but the yield stress of samples increases sharply with increasing hydrate saturation once beyond the critical value.The coefficient of volume compression and the coefficient of consolidation of hydrate-bearing samples both increase firstly and then decrease to a relative stable level with increasing vertical stress,and the transition occurs at 200 kPa.The average consolidation degree with elapsed time increases rapidly under low vertical stresses,slowly under median vertical stresses,and under high vertical stresses,the consolidation increases a little faster but still slower than those under low vertical stresses.展开更多
Low temperature and low permeability are the challenges for the development of hydrate reservoirs in permafrost.The ice produced around the production well caused by high depressurization driving force reduces the gas...Low temperature and low permeability are the challenges for the development of hydrate reservoirs in permafrost.The ice produced around the production well caused by high depressurization driving force reduces the gas production,and it is necessary to reduce the effect of ice production on gas production.In this work,a new combination of fracturing technology and depressurization method was proposed to evaluate the gas production potential at the site DK-2 in Qinghai-Tibet Plateau Permafrost.A relatively higher intrinsic permeability of the fracture zone surround the horizontal production well was created by the fracturing technology.The simulation results showed that the fracture zone reduced the blocking of production ice to production wells and promoted the propagation of production pressure.And the gas production increased by 2.1 times as the radius of the fracture zone increased from 0 to 4 m in 30 years.Nearly half of the hydrate reservoirs were dissociated in 30 years,and greater than 51.7%of the gas production was produced during the first 10 years.Moreover,production behaviours were sensitive to the depressurization driving force but not to the thermal conductivity.The growth of gas production was not obvious with the intrinsic permeability of the fracture zone higher than 100 m D.The effect of ice production on gas production by fracturing technology and depressurization method was limited.展开更多
The morphological changes in isolated bubbles in gassy silt play a critical role in the microscopic structures between soil particles and bubbles and macroscopic physical properties.Based on X-ray CT scanning experime...The morphological changes in isolated bubbles in gassy silt play a critical role in the microscopic structures between soil particles and bubbles and macroscopic physical properties.Based on X-ray CT scanning experiments under various vertical loads(four levels),self-designed acoustic macro experiments,and a series of formula revisions to the macro-air-bearing silt sound-velocity prediction model,this paper discusses the macro-and micro-scale features of gassy silts from the Yellow River Delta.The samples consisted of different proportions of silt from the Yellow River Delta and porous media,and they were used to form two types of aerosol silts with initial gas contents of 4.23%and 7.67%.The results show that the air bubble content and external load considerably affect the microstructural parameters and acoustic behavior of gassy silt in the Yellow River Delta.The macroscopic sound velocity showed a linear positive correlation with vertical load and relation to microstructural parameters in varying manners and degrees.Based on the traditional Biot-Stoll acoustic model,the gas-phase medium coefficient was introduced for the proper calculation and prediction of the sound velocity of air-bearing silt.The errors of the overall prediction varied between 5.6%and 9.6%.展开更多
To obtain the fundamental data of CO2/N2 gas mixture hydrate formation kinetics and CO2 separation and sequestration mechanisms,the gas hydrate formation process by a binary CO2/N2 gas mixture(50:50)in fine sediments(...To obtain the fundamental data of CO2/N2 gas mixture hydrate formation kinetics and CO2 separation and sequestration mechanisms,the gas hydrate formation process by a binary CO2/N2 gas mixture(50:50)in fine sediments(150–250μm)was investigated in a semibatch vessel at variable temperatures(273,275,and 277 K)and pressures(5.8–7.8 MPa).During the gas hydrate reaction process,the changes in the gaseous phase composition were determined by gas chromatography.The results indicate that the gas hydrate formation process of the binary CO2/N2 gas mixture in fine sediments can be reduced to two stages.Firstly,the dissolved gas containing a large amount of CO2 formed gas hydrates,and then gaseous N2 participated in the gas hydrate formation.In the second stage,all the dissolved gas was consumed.Thus,both gaseous CO2 and N2 diffused into sediment.The first stage in different experiments lasted for 5–15 h,and>60%of the gas was consumed in this period.The gas consumption rate was greater in the first stage than in the second stage.After the completion of gas hydrate formation,the CO2 content in the gas hydrate was more than that in the gas phase.This indicates that CO2 formed hydrate easily than N2 in the binary mixture.Higher operating pressures and lower temperatures increased the gas consumption rate of the binary gas mixture in gas hydrate formation.展开更多
The microscopic characterization of isolated bubbles in gassy soil plays an important role in the macroscopic physical properties of sediments and is a key factor in the study of geological hazards in gas-bearing stra...The microscopic characterization of isolated bubbles in gassy soil plays an important role in the macroscopic physical properties of sediments and is a key factor in the study of geological hazards in gas-bearing strata.Based on the box-counting method and the pore fractal features in porous media,a fractal model of bubble microstructure parameters in gassy soil under different gas con-tents and vertical load conditions is established by using an industrial X-ray CT scanning system.The results show that the fractal di-mension of bubbles in the sample is correlated with the volume fraction of bubbles,and it is also restricted by the vertical load.The three-dimensional fractal dimension of the sample is about 1 larger than the average two-dimensional fractal dimension of all the slices from the same sample.The uniform porous media fractal model is used to test the equivalent diameter,and the results show that the variation of the measured pore diameter ratio is jointly restricted by the volume fraction and the vertical load.In addition,the measured self-similarity interval of the bubble area distribution is tested by the porous media fractal capillary bundle model,and the fitting curve of measured pore area ratio in a small loading range is obtained in this paper.展开更多
1.Objective Natural gas hydrates are considered as a potential alternative fuel resource to petroleum and gas (Chong ZR et al.,2016),which can be exploited by means of depressurization,thermal method,inhibitor injecti...1.Objective Natural gas hydrates are considered as a potential alternative fuel resource to petroleum and gas (Chong ZR et al.,2016),which can be exploited by means of depressurization,thermal method,inhibitor injection,etc.For the thermal method,gas hydrates are decomposed into water and methane when the reservoir is heated to above the equilibrium temperature of gas hydrate (Li X et al.,2016). However,the thermal recovery method needs a great deal of heat,and thus the feasibility of economic exploitation is reduced.展开更多
The Qilian Mountain permafrost area located in the northern of Qinghai-Tibet Plateau is a favorable place for natural gas hydrate formation and enrichment,due to its well-developed fractures and abundant gas sources.U...The Qilian Mountain permafrost area located in the northern of Qinghai-Tibet Plateau is a favorable place for natural gas hydrate formation and enrichment,due to its well-developed fractures and abundant gas sources.Understanding the formation and distribution of multi-component gas hydrates in fractures is crucial in accurately evaluating the hydrate reservoir resources in this area.The hydrate formation experiments were carried out using the core samples drilled from hydrate-bearing sediments in Qilian Mountain permafrost area and the multi-component gas with similar composition to natural gas hydrates in Qilian Mountain permafrost area.The formation and distribution characteristics of multi-component gas hydrates in core samples were observed in situ by X-ray Computed Tomography(X-CT)under high pressure and low temperature conditions.Results show that hydrates are mainly formed and distributed in the fractures with good connectivity.The ratios of volume of hydrates formed in fractures to the volume of fractures are about 96.8%and 60.67%in two different core samples.This indicates that the fracture surface may act as a favorable reaction site for hydrate formation in core samples.Based on the field geological data and the experimental results,it is preliminarily estimated that the inventory of methane stored in the fractured gas hydrate in Qilian Mountain permafrost area is about 8.67×1013 m3,with a resource abundance of 8.67×108 m3/km2.This study demonstrates the great resource potential of fractured gas hydrate and also provides a new way to further understand the prospect of natural gas hydrate and other oil and gas resources in Qilian Mountain permafrost area.展开更多
China has entered the area of new normal economy which requires the harmonious development of energy consumption,environmental protection and economic development.Natural gas hydrate is a potential clean energy with t...China has entered the area of new normal economy which requires the harmonious development of energy consumption,environmental protection and economic development.Natural gas hydrate is a potential clean energy with tremendous reserve in China.The successful field test of marine hydrate exploitation in South China Sea created a new record of the longest continuous gas production from natural gas hydrate.However,the corresponding fundamental research is still urgently needed in order to narrow the gap between field test and commercial production.This paper reviewed the latest advances of experimental study on gas production from hydrate reservoir in China.The experimental apparatus for investigating the performance of hydrate dissociation in China has developed from one dimensional to two dimensional and three dimensional.In addition,well configuration developed from one tube to complicated multi-well networks to satisfy the demand of different production models.Besides,diverse testing methods have been established.The reviewed papers preliminary discussed the mechanical properties and the sediment deformation situation during the process of hydrate dissociation.However,most reported articles only consider the physical factor,the coupled mechanism of physical and chemical factor for the mechanical properties of the sediment and the sand production problem should be studied further.展开更多
1.Objectives As about 99% of the natural gas hydrate (NGH)resources are stored on the seafloor,it is inevitable that in its process of exploration and production,there will be geohazards such as methane leakage,seabed...1.Objectives As about 99% of the natural gas hydrate (NGH)resources are stored on the seafloor,it is inevitable that in its process of exploration and production,there will be geohazards such as methane leakage,seabed subsidence,ecosystem damage and even landslide.Therefore,a set of integrated systems for environmental monitoring in the process of NGH production has been proposed in the consideration of environmental disasters that may arise in the process of hydrate production.展开更多
The first marine gas hydrate drilling expedition (GMGS-1) of China was performed in the Shenhu Area, northern slope of the South China Sea (Fig. la) by Guangzhou Marine Geological Survey (GMGS) during April to J...The first marine gas hydrate drilling expedition (GMGS-1) of China was performed in the Shenhu Area, northern slope of the South China Sea (Fig. la) by Guangzhou Marine Geological Survey (GMGS) during April to June, 2007, to detect the occurrences of gas hydrates. The drilling results showed that the distributions of hydrates in the drilling area were heterogeneous.展开更多
1 Introduction In April-June of 2007, the Expedition GMGS-1 was completed successfully in the Shenhu Area of the South China Sea. Gas hydrate was detected at three (Sites SH2, SH3 and SH7) of the five sites that wer...1 Introduction In April-June of 2007, the Expedition GMGS-1 was completed successfully in the Shenhu Area of the South China Sea. Gas hydrate was detected at three (Sites SH2, SH3 and SH7) of the five sites that were cored. The Shenhu gas hydrate drilling area is located in the central Baiyun sag.展开更多
Drilling results suggest that the thickness of natural gas hydrates(NGHs)in the Shenhu Area,South China Sea(SCS)are spatially heterogenous,making it difficult to accurately assess the NGHs resources in this area.In th...Drilling results suggest that the thickness of natural gas hydrates(NGHs)in the Shenhu Area,South China Sea(SCS)are spatially heterogenous,making it difficult to accurately assess the NGHs resources in this area.In the case that free gas exists beneath hydrate deposits,the frequency of the hydrate deposits will be noticeably attenuated,with the attenuation degree mainly affected by pore development and free gas content.Therefore,the frequency can be used as an important attribute to identify hydrate reservoirs.Based on the time-frequency characteristics of deposits,this study predicted the spatial distribution of hydrates in this area using the frequency division inversion method as follows.Firstly,the support vector machine(SVM)method was employed to study the amplitude versus frequency(AVF)response based on seismic and well logging data.Afterward,the AVF response was introduced as independent information to establish the nonlinear relationship between logging data and seismic waveform.Then,the full frequency band information of the seismic data was fully utilized to obtain the results of frequency division inversion.The inversion results can effectively broaden the frequency band,reflect the NGHs distribution,and reveal the NGHs reservoirs of two types,namely the fluid migration pathway type and the in situ self-generation self-storage diffusion type.Moreover,the inversion results well coincide with the drilling results.Therefore,it is feasible to use the frequency division inversion to predict the spatial distribution of heterogeneous NGHs reservoirs,which facilitates the optimization of favorable drilling targets and is crucial to the resource potential assessment of NGHs.展开更多
The complex distribution of gas hydrate in sediments makes understanding the mechanical properties of hydrate-bearing sediments a challenging task.The mechanical behaviors of hydrate-bearing interlayered sediments are...The complex distribution of gas hydrate in sediments makes understanding the mechanical properties of hydrate-bearing sediments a challenging task.The mechanical behaviors of hydrate-bearing interlayered sediments are still poorly known.A series of triaxial shearing tests were conducted to investigate the strength parameters and deformation properties of methane hydrate-bearing interlayered sediments at the effective pressure of 1 MPa.The results indicate that the stress-strain curves of hydrate-bearing interlayered sediments are significantly different from that of hydrate-bearing sediments.The peak strength,Young's modulus,initial yielding modulus,and failure mode are deeply affected by the methane hydrate distribution.The failure behaviors and mechanism of strain softening and hardening patterns of the interlayered specimens are more complicated than those of the integrated specimens.This study compares the different mechanical behaviors between integrated and interlayered specimens containing gas hydrate,which can serve as a reference for the prediction and analysis of the deformation behaviors of natural gas hydrate reservoirs.展开更多
基金financially supported by the Natural Science Foundation of Shandong Province(No.ZR202011030013)the National Natural Science Foundation of China(No.41976205)+1 种基金the Marine S&T Fund of Shandong Province for Pilot National Laboratory for Marine Science and Technology(Qingdao)(No.2021QNLM020002)the China Geological Survey Program(No.DD20221704).
文摘It has been evidenced that shallow gas hydrate resources are abundant in deep oceans worldwide.Their geological back-ground,occurrence,and other characteristics differ significantly from deep-seated hydrates.Because of the high risk of well construction and low production efficiency,they are difficult to be recovered by using conventional oil production methods.As a result,this paper proposes an alternative design based on a combination of radial drilling,heat injection,and backfilling methods.Multi-branch holes are used to penetrate shallow gas hydrate reservoirs to expand the depressurization area,and heat injection is utilized as a supplement to improve gas production.Geotechnical information collected from an investigation site close to the offshore production well in the South China Sea is used to assess the essential components of this plan,including well construction stability and gas production behavior.It demonstrates that the hydraulic fracturing of the 60mbsf overburden layer can be prevented by regulating the drilling fluid densities.However,the traditional well structure is unstable,and the suction anchor is advised for better mechanical performance.The gas produc-tion rate can be significantly increased by combining hot water injection and depressurization methods.Additionally,the suitable produc-tion equipment already in use is discussed.
基金financial support from the Key Program of National Natural Science Foundation of China(51736009)the Natural Science Foundation of Guangdong Province,China(2023A1515012061)+3 种基金the Guangdong Special Support Program-Local innovation and entrepreneurship team project(2019BT02L278)the Special Project for Marine Economy Development of Guangdong Province(GDME-2022D043)the Fundamental Research&Applied Fundamental Research Major Project of Guangdong Province(2019B030302004,2020B030103003)the Science and Technology Apparatus Development Program of the Chinese Academy of Sciences(YZ201619),the Frontier Sciences Key Research Program of the Chinese Academy of Sciences(QYZDJSSW-JSC033)。
文摘Gas hydrate technology has considerable potential in many fields.However,due to the lack of understanding of the micro mechanism of hydrate formation,it has not been commercially applied so far.Gas hydrate formation is essentially a gas-liquid-solid phase transition of water and gas molecules at a certain temperature and pressure.The key to the hydrate formation is the transformation of water molecule from disordered arrangement to ordered arrangement.In this process,weakly hydrogen bonded water will be correspondingly converted to strongly hydrogen bonded water.Through in situ Raman analysis and experiments,the position change of the corresponding peaks of the strongly hydrogen bonded water and the weakly hydrogen bonded water was compared in this work,and the key microscopic process and influence of gas hydrate formation in different systems were comprehensively studied and summarized.It is found that,with the decrease of temperature,the OAH of the weakly hydrogen bonded water remains unchanged when the temperature drops to a certain value,which is the key to the transformation of water into cage hydrate rather than ice.The conversion from the weakly hydrogen bonded water to the strongly hydrogen bonded water is closely related to the gas-liquid interface force,the hydrophilicity/hydrophobicity of the promoter,the ionization degree of liquid,and the electrostatic field of the system.Among the four most common promoters,tetrahydrofuran(THF)has the highest efficiency in promoting methane(CH4)hydrate formation.Therefore,this study provides a scientific direction and basis for the development of high efficient hydrate formation promoters,which can effectively weaken the hydrogen bond of weakly hydrogen bonded water and promote the conversion of weakly hydrogen bonded water to strongly hydrogen bonded water.
基金supported by the National Natural Science Foundation of China(Grants 41376078,51639008,and 51239010)the China Geological Survey(Grant DD20160216)the Youth Innovation Promotion Association of Chinese Academy of Sciences(Grant 2017027)
文摘The changes in the mechanical properties of gas hydrate-bearing sediments(GHBS) induced by gas hydrate(GH) dissociation are essential to the evaluation of GH exploration and stratum instabilities. Previous studies present substantial mechanical data and constitutive models for GHBS at a given GH saturation under the non-dissociated condition. In this paper, GHBS was formed by the gas saturated method, GH was dissociated by depressurization until the GH saturation reached different dissociation degrees. The stress–strain curves were measured using triaxial tests at a same pore gas pressure and different confining pressures. The results show that the shear strength decreases progressively by 30%–90% of the initial value with GH dissociation, and the modulus decreases by 50% –75%. Simplified relationships for the modulus, cohesion, and internal friction angle with GH dissociated saturation were presented.
基金financially supported by the National Natural Science Foundation of China(No.41976205)the National Key R&D Program of China(No.2018YFC031 0000)the Open Funding of Qingdao National Laboratory for Marine Science and Technology(No.QNLM20 16ORP0203)
文摘Study of the surface morphology of gas hydrate is of great importance in understanding its physical properties and occurrence.In order to investigate the surface morphology of different types(sI and sII)and occurrences(pore-filling and fracture-filling)of gas hydrate,both lab-synthesized and drilled-gas hydrate samples were measured using cryo-scanning electron microscopy(cryo-SEM).Results showed that the surface of s I hydrate was relatively smooth,and spongy nano-pores(200–400 nm)gradually occurred at the surface during continuous observation.The surface of sII hydrate was more compact,showing a tier-like structure.Hydrate occurred in quartz sand and usually filled the pores of the sediments and both hydrate and sediments were cemented with each other.SEM observation of the gas hydrates collected from the South China Sea showed that the surface morphology and contact relation with sediments varied with hydrate occurrence.For instance,hydrates dispersed in sediments mainly filled the pores of the sediments.The existence of microorganism shells,such as foraminifera,was beneficial to the formation of gas hydrate.When hydrate occurred as a massive or vein structure,it was easily distinguished from the surrounding sediments.The surface of hydrate with massive or vein structure showed two distinct characters:one was dense and smooth,the other is porous(several to tens of micrometers in diameter).The occurrence of different hydrate morphologies was probably caused by the supplement rates of methane gas.
基金Supported by National Key Research and Development Plan of China(2017YFC0307306)the National Natural Science Foundation of China(51876211)
文摘Natural gas hydrates easily form in pipelines,causing potential safety issues during oil and gas production and transportation.Injecting gas hydrate inhibitors is one of the most effective methods for preventing gas hydrate formation or aggregation.However,some thermodynamic hydrate inhibitors are toxic and harmful to the environment,whereas degradation of kinetic inhibitors is difficult.Therefore,environmentally friendly and easily biodegradable novel green inhibitors have been proposed and investigated.This paper provides a short but systematic review of the inhibitory performance of amino acids,antifreeze proteins,and ionic liquids.For different hydrate formation systems,the influences of the inhibitor type,structure,and concentration on the inhibitory effects are summarized.The mechanism of green inhibitors as kinetic inhibitors is also discussed.The progress described here will facilitate further developments of such green inhibitors for gas hydrate formation.
基金supported financially by the National Key R&D Program of China(No.2017YFC0307600)the Qingdao National Laboratory for Marine Science and Technology(No.QNLM2016ORP0207)+3 种基金the National Natural Science Foundation of China(No.41906067)the China Postdoctoral Science Foundation(No.2018M632634)the Natural Science Foundation of Shandong Province of China(No.ZR2019BD051)the Marine Geological Survey Program(Nos.DD20190221 and DD20190231)。
文摘Gas leakage is an important consideration in natural systems that experience gas hydrate accumulation.A number of velocity models have been created to study hydrate-bearing sediments,including the BGTL theory,the weighted equation,the Wood equation,the K-T equation,and the effective medium theory.In previous work,we regarded water as the pore fluid,which meant its density and bulk modulus values were those of water.This approach ignores the presence of gas,which results in a biased calculation of the pore fluid's bulk modulus and density.To take into account the effect of gas on the elastic wave velocity,it is necessary to recalculate the bulk modulus and density of an equivalent medium.Thus,a high-pressure reactor device for simulating leakage systems was developed to establish the relationship between wave velocity and hydrate saturation in methane-flux mode.A comparison of the values calculated by the velocity model with the experimental data obtained in this study indicates that the effective medium theory(EMT,which considers gas effects)is more applicable than other models.For hydrate saturations of 10%–30%,the result ranges between EMT-B(homogenous gas distribution)and EMT-B(patchy gas distribution).For hydrate saturations of 30%–60%,the results are similar to those of the EMT-B(homogenous gas distribution)mode,whereas hydrate saturations of 60%–70%yield results similar to those of the EMT-A mode.For hydrate saturations greater than 80%,the experimental results are similar to those of the EMT-B mode.These results have significance for hydrate exploitation in the South China Sea.
基金supported by the Qingdao Natural Science Foundation(No.23-2-1-54-zyyd-jch)the National Natural Science Foundation of China(Nos.42076217,41976074)+1 种基金the Laoshan Laboratory(No.LSKJ202203506)the Key Laboratory of Geotechnical and Underground Engineering of Ministry of Education,Tongji University(No.KLE-TJGE-G2202).
文摘The safe and efficient development of natural gas hydrate requires a deep understanding of the deformation behaviors of reservoirs.In this study,a series of triaxial shearing tests are carried out to investigate the deformation properties of hydrate-bearing sediments.Variations of volumetric and lateral strains versus hydrate saturation are analyzed comprehensively.Results indicate that the sediments with high hydrate saturation show dilative behaviors,which lead to strain-softening characteristics during shearing.The volumetric strain curves have a tendency to transform gradually from dilatation to compression with the increase in effective confining pressure.An easy prediction model is proposed to describe the relationship between volumetric and axial strains.The model coefficientβis the key dominating factor for the shape of volumetric strain curves and can be determined by the hydrate saturation and stress state.Moreover,a modified model is established for the calculation of lateral strain.The corresponding determination method is provided for the easy estimation of model coefficients for medium sand sediments containing hydrate.This study provides a theoretical and experimental reference for deformation estimation in natural gas hydrate development.
基金jointly supported by the Natural Science Foundation of Shandong Province (No.ZR2022YQ54)the Marine S&T Fund of Shandong Province for Laoshan Laboratory (No.2021QNLM020002)the Taishan Scholars Program (No.tsqn202306297)。
文摘Mechanical properties of hydrate-bearing fine-grained sediments are crucial to effectively mitigate environmental risks caused by artificial and natural decomposition of natural gas hydrates,and the decomposition can induce laterally confined deformation.To explore the effect of natural gas hydrates on laterally confined compression properties,consolidation tests are conducted on remolded hydrate-free and hydrate-bearing samples by using natural fine-grained sediments collected from the northern South China Sea as the host sediments,and empirical equations are developed based on the analyses of consolidation characteristics.The results show that vertical loading induces a reduction in void ratio,and the reduction increases with decreasing hydrate saturation when samples are subjected to the same vertical stress change.The compression index of samples is about 0.53 whether there is hydrate or not,but the yield stress of samples increases sharply with increasing hydrate saturation once beyond the critical value.The coefficient of volume compression and the coefficient of consolidation of hydrate-bearing samples both increase firstly and then decrease to a relative stable level with increasing vertical stress,and the transition occurs at 200 kPa.The average consolidation degree with elapsed time increases rapidly under low vertical stresses,slowly under median vertical stresses,and under high vertical stresses,the consolidation increases a little faster but still slower than those under low vertical stresses.
基金support of the Key Program of National Natural Science Foundation of China(51736009)National Natural Science Foundation of China(51676196,51976228)+4 种基金Guangdong Special Support Program(2019BT02L278)Frontier Sciences Key Research Program of the Chinese Academy of Sciences(QYZDJSSW-JSC033,QYZDB-SSW-JSC028,ZDBS-LY-SLH041)Science and Technology Apparatus Development Program of the Chinese Academy of Sciences(YZ201619)the National Key R&D Program of China(2017YFC0307306)Special Project for Marine Economy Development of Guangdong Province(GDME-2018D002,GDME-2020D044)。
文摘Low temperature and low permeability are the challenges for the development of hydrate reservoirs in permafrost.The ice produced around the production well caused by high depressurization driving force reduces the gas production,and it is necessary to reduce the effect of ice production on gas production.In this work,a new combination of fracturing technology and depressurization method was proposed to evaluate the gas production potential at the site DK-2 in Qinghai-Tibet Plateau Permafrost.A relatively higher intrinsic permeability of the fracture zone surround the horizontal production well was created by the fracturing technology.The simulation results showed that the fracture zone reduced the blocking of production ice to production wells and promoted the propagation of production pressure.And the gas production increased by 2.1 times as the radius of the fracture zone increased from 0 to 4 m in 30 years.Nearly half of the hydrate reservoirs were dissociated in 30 years,and greater than 51.7%of the gas production was produced during the first 10 years.Moreover,production behaviours were sensitive to the depressurization driving force but not to the thermal conductivity.The growth of gas production was not obvious with the intrinsic permeability of the fracture zone higher than 100 m D.The effect of ice production on gas production by fracturing technology and depressurization method was limited.
基金supported by the National Natural Science Foundation of China(No.U2006213)the China Post doctoral Science Foundation(No.2022M712989).
文摘The morphological changes in isolated bubbles in gassy silt play a critical role in the microscopic structures between soil particles and bubbles and macroscopic physical properties.Based on X-ray CT scanning experiments under various vertical loads(four levels),self-designed acoustic macro experiments,and a series of formula revisions to the macro-air-bearing silt sound-velocity prediction model,this paper discusses the macro-and micro-scale features of gassy silts from the Yellow River Delta.The samples consisted of different proportions of silt from the Yellow River Delta and porous media,and they were used to form two types of aerosol silts with initial gas contents of 4.23%and 7.67%.The results show that the air bubble content and external load considerably affect the microstructural parameters and acoustic behavior of gassy silt in the Yellow River Delta.The macroscopic sound velocity showed a linear positive correlation with vertical load and relation to microstructural parameters in varying manners and degrees.Based on the traditional Biot-Stoll acoustic model,the gas-phase medium coefficient was introduced for the proper calculation and prediction of the sound velocity of air-bearing silt.The errors of the overall prediction varied between 5.6%and 9.6%.
基金Supported by the National Key Research and Development Plan of China(2017YFC0307306)National Natural Science Foundation of China(51676197,51576197)+2 种基金CAS Program(KGZD-EW-301)Guangzhou Science and Technology Project(201804010411)Youth Innovation Promotion Association CAS
文摘To obtain the fundamental data of CO2/N2 gas mixture hydrate formation kinetics and CO2 separation and sequestration mechanisms,the gas hydrate formation process by a binary CO2/N2 gas mixture(50:50)in fine sediments(150–250μm)was investigated in a semibatch vessel at variable temperatures(273,275,and 277 K)and pressures(5.8–7.8 MPa).During the gas hydrate reaction process,the changes in the gaseous phase composition were determined by gas chromatography.The results indicate that the gas hydrate formation process of the binary CO2/N2 gas mixture in fine sediments can be reduced to two stages.Firstly,the dissolved gas containing a large amount of CO2 formed gas hydrates,and then gaseous N2 participated in the gas hydrate formation.In the second stage,all the dissolved gas was consumed.Thus,both gaseous CO2 and N2 diffused into sediment.The first stage in different experiments lasted for 5–15 h,and>60%of the gas was consumed in this period.The gas consumption rate was greater in the first stage than in the second stage.After the completion of gas hydrate formation,the CO2 content in the gas hydrate was more than that in the gas phase.This indicates that CO2 formed hydrate easily than N2 in the binary mixture.Higher operating pressures and lower temperatures increased the gas consumption rate of the binary gas mixture in gas hydrate formation.
基金supported by the Open Research Fund Program of State Key Laboratory of Hydroscience and Engineering(No.sk lhse-2022-D-03)the National Natural Science Foundation of China(Nos.U2006213,42277139)the Taishan Scholars Program(No.tsqn202306297).
文摘The microscopic characterization of isolated bubbles in gassy soil plays an important role in the macroscopic physical properties of sediments and is a key factor in the study of geological hazards in gas-bearing strata.Based on the box-counting method and the pore fractal features in porous media,a fractal model of bubble microstructure parameters in gassy soil under different gas con-tents and vertical load conditions is established by using an industrial X-ray CT scanning system.The results show that the fractal di-mension of bubbles in the sample is correlated with the volume fraction of bubbles,and it is also restricted by the vertical load.The three-dimensional fractal dimension of the sample is about 1 larger than the average two-dimensional fractal dimension of all the slices from the same sample.The uniform porous media fractal model is used to test the equivalent diameter,and the results show that the variation of the measured pore diameter ratio is jointly restricted by the volume fraction and the vertical load.In addition,the measured self-similarity interval of the bubble area distribution is tested by the porous media fractal capillary bundle model,and the fitting curve of measured pore area ratio in a small loading range is obtained in this paper.
基金the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB06020204)Natural Science Foundation of China (41606087 and 91858208)the Marine Geological Survey project of China Geological Survey (DD20160218).
文摘1.Objective Natural gas hydrates are considered as a potential alternative fuel resource to petroleum and gas (Chong ZR et al.,2016),which can be exploited by means of depressurization,thermal method,inhibitor injection,etc.For the thermal method,gas hydrates are decomposed into water and methane when the reservoir is heated to above the equilibrium temperature of gas hydrate (Li X et al.,2016). However,the thermal recovery method needs a great deal of heat,and thus the feasibility of economic exploitation is reduced.
基金the financial support of the National Natural Science Foundation of China(42176212,41976074 and 41302034)the Marine S&T Fund of Shandong Province for Laoshan Laboratory(2021QNLM020002)the Marine Geological Survey Program(DD20221704)。
文摘The Qilian Mountain permafrost area located in the northern of Qinghai-Tibet Plateau is a favorable place for natural gas hydrate formation and enrichment,due to its well-developed fractures and abundant gas sources.Understanding the formation and distribution of multi-component gas hydrates in fractures is crucial in accurately evaluating the hydrate reservoir resources in this area.The hydrate formation experiments were carried out using the core samples drilled from hydrate-bearing sediments in Qilian Mountain permafrost area and the multi-component gas with similar composition to natural gas hydrates in Qilian Mountain permafrost area.The formation and distribution characteristics of multi-component gas hydrates in core samples were observed in situ by X-ray Computed Tomography(X-CT)under high pressure and low temperature conditions.Results show that hydrates are mainly formed and distributed in the fractures with good connectivity.The ratios of volume of hydrates formed in fractures to the volume of fractures are about 96.8%and 60.67%in two different core samples.This indicates that the fracture surface may act as a favorable reaction site for hydrate formation in core samples.Based on the field geological data and the experimental results,it is preliminarily estimated that the inventory of methane stored in the fractured gas hydrate in Qilian Mountain permafrost area is about 8.67×1013 m3,with a resource abundance of 8.67×108 m3/km2.This study demonstrates the great resource potential of fractured gas hydrate and also provides a new way to further understand the prospect of natural gas hydrate and other oil and gas resources in Qilian Mountain permafrost area.
基金Supported by Key Program of National Natural Science Foundation of China(51736009)National Natural Science Foundation of China(51806251 and 51676190)+5 种基金Youth Innovation Promotion Association,CAS(2019338)Pearl River S and T Nova Program of Guangzhou(201610010164)International S&T Cooperation Programme of China(2015DFA61790)Science and Technology Apparatus Development Program of the Chinese Academy of Sciences(YZ201619)Frontier Sciences Key Research Program of the Chinese Academy of Sciences(QYZDJ-SSW-JSC033)National Key Research and Development Program of China(2016YFC0304002,2017YFC0307306)
文摘China has entered the area of new normal economy which requires the harmonious development of energy consumption,environmental protection and economic development.Natural gas hydrate is a potential clean energy with tremendous reserve in China.The successful field test of marine hydrate exploitation in South China Sea created a new record of the longest continuous gas production from natural gas hydrate.However,the corresponding fundamental research is still urgently needed in order to narrow the gap between field test and commercial production.This paper reviewed the latest advances of experimental study on gas production from hydrate reservoir in China.The experimental apparatus for investigating the performance of hydrate dissociation in China has developed from one dimensional to two dimensional and three dimensional.In addition,well configuration developed from one tube to complicated multi-well networks to satisfy the demand of different production models.Besides,diverse testing methods have been established.The reviewed papers preliminary discussed the mechanical properties and the sediment deformation situation during the process of hydrate dissociation.However,most reported articles only consider the physical factor,the coupled mechanism of physical and chemical factor for the mechanical properties of the sediment and the sand production problem should be studied further.
基金the Natural Science Foundation of China (41606086 and 91858208)National Key Research and Development Program (2017YFC0307704)the Marine Geological Survey project of China Geological Survey (DD20160218).
文摘1.Objectives As about 99% of the natural gas hydrate (NGH)resources are stored on the seafloor,it is inevitable that in its process of exploration and production,there will be geohazards such as methane leakage,seabed subsidence,ecosystem damage and even landslide.Therefore,a set of integrated systems for environmental monitoring in the process of NGH production has been proposed in the consideration of environmental disasters that may arise in the process of hydrate production.
基金supported by the Open Fund(PLC201402) of State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation(Chengdu University of Technology)the PetroChina Innovation Foundation(Grant No.2013D-5006-0105)
文摘The first marine gas hydrate drilling expedition (GMGS-1) of China was performed in the Shenhu Area, northern slope of the South China Sea (Fig. la) by Guangzhou Marine Geological Survey (GMGS) during April to June, 2007, to detect the occurrences of gas hydrates. The drilling results showed that the distributions of hydrates in the drilling area were heterogeneous.
文摘1 Introduction In April-June of 2007, the Expedition GMGS-1 was completed successfully in the Shenhu Area of the South China Sea. Gas hydrate was detected at three (Sites SH2, SH3 and SH7) of the five sites that were cored. The Shenhu gas hydrate drilling area is located in the central Baiyun sag.
基金supported by the National Research and Development Fund entitled“High Precision Characterization Technology of Natural Gas Hydrates Reservoirs”(2017YFC0307406)the projects entitled“Integrated Observation Data Integration and Application Service of Natural Resource Elements”(DD20208067)+2 种基金“Comprehensive geological survey of coastal zone and reef in the Northern Jiaodong”(ZD20220604)initiated by the China Geological Surveythe project entitled“Study on Hydrocarbon Accumulation Failure and Fluid Evolution Reduction of the Permian Reservoir in the Laoshan Uplift,South Yellow Sea”(42076220)“Temporal and Spatial Distribution Characteristics and Provenance of Two Stages Paleo-deltas on the Outer Shelf in the North of the East China Sea since Late Pleistocene”(41706069)organized by the National Natural Science Foundation of China。
文摘Drilling results suggest that the thickness of natural gas hydrates(NGHs)in the Shenhu Area,South China Sea(SCS)are spatially heterogenous,making it difficult to accurately assess the NGHs resources in this area.In the case that free gas exists beneath hydrate deposits,the frequency of the hydrate deposits will be noticeably attenuated,with the attenuation degree mainly affected by pore development and free gas content.Therefore,the frequency can be used as an important attribute to identify hydrate reservoirs.Based on the time-frequency characteristics of deposits,this study predicted the spatial distribution of hydrates in this area using the frequency division inversion method as follows.Firstly,the support vector machine(SVM)method was employed to study the amplitude versus frequency(AVF)response based on seismic and well logging data.Afterward,the AVF response was introduced as independent information to establish the nonlinear relationship between logging data and seismic waveform.Then,the full frequency band information of the seismic data was fully utilized to obtain the results of frequency division inversion.The inversion results can effectively broaden the frequency band,reflect the NGHs distribution,and reveal the NGHs reservoirs of two types,namely the fluid migration pathway type and the in situ self-generation self-storage diffusion type.Moreover,the inversion results well coincide with the drilling results.Therefore,it is feasible to use the frequency division inversion to predict the spatial distribution of heterogeneous NGHs reservoirs,which facilitates the optimization of favorable drilling targets and is crucial to the resource potential assessment of NGHs.
基金supported by the National Natural Science Foundation of China (No. 41976074)National Key Research and Development Plan (No. 2017YFC030 7600)+2 种基金the Taishan Scholar Special Experts Project (No. ts201712079)Qingdao National Laboratory for Marine Science and Technology (No. QNLM2016ORP0207)the Graduate School Innovation Program of China University of Petroleum (East China) (No. YCX2019020)
文摘The complex distribution of gas hydrate in sediments makes understanding the mechanical properties of hydrate-bearing sediments a challenging task.The mechanical behaviors of hydrate-bearing interlayered sediments are still poorly known.A series of triaxial shearing tests were conducted to investigate the strength parameters and deformation properties of methane hydrate-bearing interlayered sediments at the effective pressure of 1 MPa.The results indicate that the stress-strain curves of hydrate-bearing interlayered sediments are significantly different from that of hydrate-bearing sediments.The peak strength,Young's modulus,initial yielding modulus,and failure mode are deeply affected by the methane hydrate distribution.The failure behaviors and mechanism of strain softening and hardening patterns of the interlayered specimens are more complicated than those of the integrated specimens.This study compares the different mechanical behaviors between integrated and interlayered specimens containing gas hydrate,which can serve as a reference for the prediction and analysis of the deformation behaviors of natural gas hydrate reservoirs.