Theoretical Study On The Stability Of Natural Gas Hydrate Drilling

Natural gas hydrate has many merits, such as high energy density, widedistribution, abundant resource, shallow buried and so on. It will be an idealsubstitute of the petroleum. Drilling is the most direct and primary technicalmeans to explore and exploit natural gas hydrate, however, how to keep thestabilityofdrillingis thekeytodrill andexploit natural gas hydratesafelyandefficiently.This paper has conducted the theoretical study on the stability of natural gashydrate drilling. Based on the theories of mass conservation, momentumconservation, energy conservation and heat transfer, the mathematical modelfor predicting wellbore pressure and temperature distributions while drillingisestablished.OnthebaseofRoadifermodel,theone-dimensional mathematicalmodel of reservoir hydrate dissociation is established and the numericalsimulation software is compiled. Factors that affect the hydrate dissociationare analyzed using the numerical simulation software. The result shows thatthe bottom hole temperature and pressure of drillingfluid have great influenceon the hydrate dissociation rate. In order to control the hydrate dissociationand keep good stability during the drilling through the hydrate reservoir thebottom hole temperature of drilling fluid should be reduced mainly and the bottom hole pressure of drillingfluid should be increased appropriately. Also,factors that affect the temperature and pressure are analyzed to providetheoreticalguidanceforhydratedrillingparameterdesign.