Study On The Phase Behavior Law Of The Hydrates In The Wellbore During Drilling Of Marine Gas Hydrate

Marine natural gas resources are very abundant,but because of their unique properties,phase changes occur in the wellbore during the drilling of natural gas hydrates: during drilling,the hydrate formation decomposes gas,then the gas enters the wellbore and rises.When the temperature and pressure meet the conditions,the hydrate will be generated again,and once it is separated from the production area,it will be decomposed again.This makes traditional drillings subject more challenging,therefore,it is necessary to study the law of the phase behavior of the hydrates in the wellbore.Based on the analysis of physicochemical properties and structural characteristics of hydrates,this paper compares the ocean hydrate reservoirs with conventional subsea oil and gas reservoirs,and deals with the problems encountered in hydrate drilling and the existing hydrate drilling technologies.A preliminary exploration was conducted.Computer simulations of the hydrate phase equilibrium curves were compared and selected with appropriate models.The effects of different types of natural gas components,different types of hydrate inhibitors,and concentrations on the phase equilibrium curve were analyzed;The dynamics and decomposition kinetics were established,and the hydrate formation and decomposition rate equations in the wellbore were established.The model was validated with the help of literature and a simple simulation of phase hydrate changes was considered.Considering the changes in the phase state of natural gas hydrates,The multi-phase flow equations for wellbore in the process of ocean hydrate drilling were established.The temperature and pressure fields in the wellbore were simulated by numerical calculation.Combined with actual calculation examples,the phase behavior of hydrates in the wellbore was predicted and the drilling parameters were analyzed.The effect of hydrate formation in the wellbore.According to the calculation results,the temperature and pressure changes in the wellbore are the main factors affecting the change of the hydrate phase state.In the actual drilling,the wellbore temperature and pressure can be effectively controlled to prevent drilling accidents by adjusting the drilling parameters.