Prediction of gas hydrate formation region in the wellbore of deepwater drilling

It is essential to consider the thermodynamics, temperature, and pressure conditions of gas hydrate formation in order to predict the gas hydrate formation region in the wellbore of deepwater drilling. Multiphase flow governing equations (including continuity equation and momentum conservation equation), temperature field equations in annulus and drill pipe, and hydrate formation thermodynamics equation are established based on the characteristics of deepwater drilling. The definite conditions, discrete methods, and iterative steps are given to solve the equations under different working conditions. Through examples of calculation, the impacts of relevant parameters on gas hydrate formation region during drilling, off drilling, and well killing process are discussed. The result shows that the hydrate formation region is getting small when circulation volume becomes great, inhibitor concentration becomes high, downtime becomes short, or choke line size becomes large. And the result also indicates that it is more efficient to consider multifactors to suppress hydrate formation. The parameters can be optimized based on the method.