Experiment of Formate Drilling Fluid for Drilling in Marine Gas Hydrate Bearing Sediments

When drilling in marine gas hydrate bearing sediments,the decomposition of gas hydrate and the entering of the released gas into the mud circulating system and reforming gas hydrate are key factors that affect the safety of drilling operation. In order to develop a drilling fluid that can ensure safe drilling,the authors utilized the natural gas hydrate simulation experimental system,and evaluated the effect of bentonite on the rheological property of formate drilling fluid at low temperature,the rheological property of formate drilling fluid without bentonite at low temperature,and the performance of kinetic hydrate inhibitor PVPK-30 and PVPK-90.The experiment indicates that with the addition of bentonite,the viscosity and shearing force of formate drilling fluid increase rapidly at low temperature while the formulation without bentonite has a steady rheological parameter at the same circumstances. At the temperature of -4℃ and pressure of 18MPa,PVPK-90 has better performance than PVPK-30,and an addition of 1% wt of PVPK-90 in formate drilling fluid can effectively inhibit the formation of gas hydrate.