Invasion of drilling fluid into natural gas hydrate deposits during drilling might damage the reservoir,induce hydrate dissociation and then cause wellbore instability and distortion of the data from well logging. Add...Invasion of drilling fluid into natural gas hydrate deposits during drilling might damage the reservoir,induce hydrate dissociation and then cause wellbore instability and distortion of the data from well logging. Adding nanoparticles into drilling fluid is an effective method in reducing the invasion of drilling fluid and enhancing borehole stability. However, the addition of nanoparticles might also introduce hydrate formation risk in borehole because they can act as the "seeds" for hydrate nucleation. This paper presents an experimental study of the effect of hydrophilic silica nanoparticle on gas hydrate formation in a dynamic methane/liquid-water system. In the experiment, the ultrapure water with and without1.0 wt%–6.0 wt% concentrations of silica nanoparticles, grain sizes of 20 and 50 nm, were pressurized by methane gas under varied conditions of temperature and pressure. The induction time, the gas consumption, and the average rate of gas consumption in the system were measured and compared to those in ultrapure water. The results show that a concentration of 4.0 wt% hydrophilic SiO_2 particles with a grain size of 50 nm has a relatively strong inhibition effect on hydrate formation when the initial experimental condition is 5.0 °C and 5.0 MPa. Compared to ultrapure water, the hydrophilic nano-SiO_2 fluid increases the induction time for hydrate formation by 194% and decreases the amount and average rate of hydrate formation by 10% and 17%, respectively. This inhibition effect may be attributed to the hydrophilicity,amount and aggregation of silica nanoparticle according to the results of water activity and zeta potential measurements. Our work also elucidates hydrophilic, instead of hydrophobic, nanoparticles can be added to the drilling fluid to maintain wellbore stability and to protect the hydrate reservoir from drilling mud damage, because they exhibit certain degree of hydrate inhibition which can reduce the risk of hydrate reformation and aggregation during gas hydrate or deep water drilling if展开更多
Gas hydrate-caused pipeline plugging is an industrial nuisance for petroleum flow assurance that calls for technological innovations.Traditional thermodynamic inhibitors such as glycols and inorganic salts suffer from...Gas hydrate-caused pipeline plugging is an industrial nuisance for petroleum flow assurance that calls for technological innovations.Traditional thermodynamic inhibitors such as glycols and inorganic salts suffer from high dosing,environmental unfriendliness,corrosiveness,and economical burden.The development and use of kinetic hydrate inhibitors(KHIs),mostly polymeric compounds,with their inhibiting effects on hydrate nucleation and growth are considered an effective and economically viable chemical treatment for hydrate prevention.However,the actual performance of a KHI candidate is dependent on various factors including its chemical structure,molecular weight,spatial configuration,effective concentration,pressure and temperature,evaluation methods,use of other additives,etc.This review provides a short but systematic overview of the fundamentals of natural gas hydrates,the prevailing categories of polymeric kinetic hydrate inhibitors with proposed inhibition mechanisms,and the various synergists studied for boosting the KHI performance.Further research endeavors are in need to unveil the KHI working modes under different conditions.The conjunctive use of KHIs and synergists may facilitate the commercial application of effective KHIs to tackle the hydrate plugging problem in the oil and gas flow assurance practices.展开更多
Insights into the mechanism of hydrate nucleation are of great significance for the development of hydrate-based technologies,hydrate relevant flow assurance,and the exploration of in situ natural gas hydrates.Compare...Insights into the mechanism of hydrate nucleation are of great significance for the development of hydrate-based technologies,hydrate relevant flow assurance,and the exploration of in situ natural gas hydrates.Compared with the thermodynamics of hydrate formation,understanding the nucleation mechanism is challenging and has drawn substantial attention in recent decades.In this paper,we attempt to give a comprehensive review of the recent progress of studies of clathrate hydrate nucleation.First,the existing hypotheses on the hydrate nucleation mechanism are introduced and discussed.Then,we summarize recent experimental studies on induction time,a key parameter evaluating the velocity of the nucleation process.Subsequently,the memory effect is particularly discussed,followed by the suggestion of several promising research perspectives.展开更多
There are many factors affecting the instability of the submarine hydrate-bearing slope (SHBS),and the interaction with hydrate is very complicated.In this paper,the mechanical mechanism of the static liquefaction and...There are many factors affecting the instability of the submarine hydrate-bearing slope (SHBS),and the interaction with hydrate is very complicated.In this paper,the mechanical mechanism of the static liquefaction and instability of submarine slope caused by the dissociation of natural gas hydrate (NGH) resulting in the rapid increase of pore pressure of gas hydrate-bearing sediments (GHBS) and the decrease of effective stress are analyzed based on the time series and type of SHBS.Then,taking the typical submarine slope in the northern South China Sea as an example,four important factors affecting the stability of SHBS are selected,such as the degree of hydrate dissociation,the depth of hydrate burial,the thickness of hydrate,and the depth of seawater.According to the principle of orthogonal method,25 orthogonal test schemes with 4 factors and 5 levels are designed and the safety factors of submarine slope stability of each scheme are calculated by using the strength reduction finite element method.By means of the orthogonal design range analysis and the variance analysis,sensitivity of influential factors on stability of SHBS are obtained.The results show that the degree of hydrate dissociation is the most sensitive,followed by hydrate burial depth,the thickness of hydrate and the depth of seawater.Finally,the concept of gas hydrate critical burial depth is put forward according to the influence law of gas hydrate burial depth,and the numerical simulation for specific submarine slope is carried out,which indicates the existence of critical burial depth.展开更多
基金supported by National Youth Top-notch Talent Support Programthe National Natural Science Foundationof China(41672367,51704266)+2 种基金China Geological Survey Project(DD20160216)Qingdao National Laboratory for Marine Science and Technology Open Fund(QNLM2016ORP0203)Experimental Apparatus Improvement Program of CUG(SJ-201613)
文摘Invasion of drilling fluid into natural gas hydrate deposits during drilling might damage the reservoir,induce hydrate dissociation and then cause wellbore instability and distortion of the data from well logging. Adding nanoparticles into drilling fluid is an effective method in reducing the invasion of drilling fluid and enhancing borehole stability. However, the addition of nanoparticles might also introduce hydrate formation risk in borehole because they can act as the "seeds" for hydrate nucleation. This paper presents an experimental study of the effect of hydrophilic silica nanoparticle on gas hydrate formation in a dynamic methane/liquid-water system. In the experiment, the ultrapure water with and without1.0 wt%–6.0 wt% concentrations of silica nanoparticles, grain sizes of 20 and 50 nm, were pressurized by methane gas under varied conditions of temperature and pressure. The induction time, the gas consumption, and the average rate of gas consumption in the system were measured and compared to those in ultrapure water. The results show that a concentration of 4.0 wt% hydrophilic SiO_2 particles with a grain size of 50 nm has a relatively strong inhibition effect on hydrate formation when the initial experimental condition is 5.0 °C and 5.0 MPa. Compared to ultrapure water, the hydrophilic nano-SiO_2 fluid increases the induction time for hydrate formation by 194% and decreases the amount and average rate of hydrate formation by 10% and 17%, respectively. This inhibition effect may be attributed to the hydrophilicity,amount and aggregation of silica nanoparticle according to the results of water activity and zeta potential measurements. Our work also elucidates hydrophilic, instead of hydrophobic, nanoparticles can be added to the drilling fluid to maintain wellbore stability and to protect the hydrate reservoir from drilling mud damage, because they exhibit certain degree of hydrate inhibition which can reduce the risk of hydrate reformation and aggregation during gas hydrate or deep water drilling if
基金Supported by China Postdoctoral Science Foundation Funded Project(2017M620050)
文摘Gas hydrate-caused pipeline plugging is an industrial nuisance for petroleum flow assurance that calls for technological innovations.Traditional thermodynamic inhibitors such as glycols and inorganic salts suffer from high dosing,environmental unfriendliness,corrosiveness,and economical burden.The development and use of kinetic hydrate inhibitors(KHIs),mostly polymeric compounds,with their inhibiting effects on hydrate nucleation and growth are considered an effective and economically viable chemical treatment for hydrate prevention.However,the actual performance of a KHI candidate is dependent on various factors including its chemical structure,molecular weight,spatial configuration,effective concentration,pressure and temperature,evaluation methods,use of other additives,etc.This review provides a short but systematic overview of the fundamentals of natural gas hydrates,the prevailing categories of polymeric kinetic hydrate inhibitors with proposed inhibition mechanisms,and the various synergists studied for boosting the KHI performance.Further research endeavors are in need to unveil the KHI working modes under different conditions.The conjunctive use of KHIs and synergists may facilitate the commercial application of effective KHIs to tackle the hydrate plugging problem in the oil and gas flow assurance practices.
基金Supported by the National Key Research and Development Program of China(2016YFC0304003,2017YFC0307302)the National Natural Science Foundation of China(21636009,51576209,21522609)the Innovative Talents Support Program for Postgraduates(BX201700288)
文摘Insights into the mechanism of hydrate nucleation are of great significance for the development of hydrate-based technologies,hydrate relevant flow assurance,and the exploration of in situ natural gas hydrates.Compared with the thermodynamics of hydrate formation,understanding the nucleation mechanism is challenging and has drawn substantial attention in recent decades.In this paper,we attempt to give a comprehensive review of the recent progress of studies of clathrate hydrate nucleation.First,the existing hypotheses on the hydrate nucleation mechanism are introduced and discussed.Then,we summarize recent experimental studies on induction time,a key parameter evaluating the velocity of the nucleation process.Subsequently,the memory effect is particularly discussed,followed by the suggestion of several promising research perspectives.
基金the National Natural Science Foundation of China (11572165)the China Geological Survey (DD20160217).
文摘There are many factors affecting the instability of the submarine hydrate-bearing slope (SHBS),and the interaction with hydrate is very complicated.In this paper,the mechanical mechanism of the static liquefaction and instability of submarine slope caused by the dissociation of natural gas hydrate (NGH) resulting in the rapid increase of pore pressure of gas hydrate-bearing sediments (GHBS) and the decrease of effective stress are analyzed based on the time series and type of SHBS.Then,taking the typical submarine slope in the northern South China Sea as an example,four important factors affecting the stability of SHBS are selected,such as the degree of hydrate dissociation,the depth of hydrate burial,the thickness of hydrate,and the depth of seawater.According to the principle of orthogonal method,25 orthogonal test schemes with 4 factors and 5 levels are designed and the safety factors of submarine slope stability of each scheme are calculated by using the strength reduction finite element method.By means of the orthogonal design range analysis and the variance analysis,sensitivity of influential factors on stability of SHBS are obtained.The results show that the degree of hydrate dissociation is the most sensitive,followed by hydrate burial depth,the thickness of hydrate and the depth of seawater.Finally,the concept of gas hydrate critical burial depth is put forward according to the influence law of gas hydrate burial depth,and the numerical simulation for specific submarine slope is carried out,which indicates the existence of critical burial depth.
