Study On Laws Of Gas–liquid–solid Three Phase Flows In Horizontal Wellbore Considering Gas Hydrate Phase Transition

In the exploitation of natural gas hydrates,horizontal wells can effectively increase the contact area and expand the decomposition range of natural gas hydrates,thereby increasing the gas production rate.However,due to the special environment of low temperature and high pressure in natural gas hydrate reservoirs,secondary generation and decomposition of hydrates occur in the wellbore during the production of horizontal wells,affecting the flow laws in the wellbore and even plugging the wellbore.Therefore,studying the law of horizontal wellbore multiphase flow considering natural gas hydrate phase transition has important implications for the exploitation of natural gas hydrate reservoirs using horizontal wells.Based on the mathematical model of gas-liquid two-phase flow in the traditional horizontal wellbore,combined with the kinetic model of gas hydrate formation/decomposition,a multiphase flow model for horizontal wellbore considering hydrate phase transition was established.The phase flow model is verified.The verification results show that the basic mathematical model has high reliability and can guarantee the accuracy of the calculation result.It can ensure that the comprehensive mathematical model established on the basic mathematical model has certain reliability.Based on the equilibrium temperature distribution between the temperature in the wellbore and the natural gas hydrate phase,a method for distinguishing the hydrate generation region was established,and the regularity of the wellbore flow considering the hydrate phase transition was recognized.The study shows that,at the same time,when the temperature and pressure conditions in the wellbore satisfy the temperature and pressure conditions required for hydrate formation,along the direction of fluid flow,the deposition thickness of natural gas hydrate on the wellbore wall surface gradually decreases,and the effective diameter of the wellbore gradually recovers to the original diameter and gas production increase continuously.As the production time increases,the deposition thickness of natural gas hydrates on the wellbore wall surface increases,and the effective diameter of the wellbore within the formation area decreases.The law of the formation of natural gas hydrates and the effect of phase change on wellbore flow under different production conditions are studied.Research shows that at the same time,the greater the inlet pressure,the larger the formation area,and the greater the ambient temperature and gas production at the wellhead,the smaller the production area;the different production time will not affect the formation area,however,the longer the production time,the greater the degree of undercooling,the easier the formation of hydrates;the generation of hydrates will result in smaller effective wellbore diameter and larger horizontal differential pressure,the gas production profile is reduced,and the gas flow rate in the formation area is increased.