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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 bore-hole 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 ul-trapure water with and without 1.0~6.0wt% concentrations of silica nanoparticles,grain sizes of 20nm and 50nm,were pressurized by methane gas under varied conditions of tem-perature 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 wa-ter.The results show that a concentration of 4.0wt% hydrophilic SiO2 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℃ and 5.0MPa.Compared to ultrapure water,the hydrophilic nano-SiO2fluid increases the induction time for hydrate formation by 194% and decreases the amount and average rate of hydrate formation by 10% and 17%,re-spectively.This inhibition effect may be attributed to the hydrophilicity,amount and ag-gregation 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 hy-drate inhibition which can reduce the risk of hydrate reformation and aggregation during gas hydrate or deep water drilling if their concentration can be controlled properly.