PREDICTION OF GAS HYDRATE FORMATION CONDITIONS IN WELLBORE

Empirical formula,phase equilibrium and statistical thermodynamics are major prediction methods for gas hydrate formation conditions.Among them,the phase equilibrium method is not applicable in gas field with higher content of non-hydrocarbon(e.g.content of CO₂ in Yaoyingtai Gas Field is up to 22%,so the method is not applicable),and the statistical thermodynamics involves many parameters,so it is not convenient to be used in practice.The methods for calculating wellbore pressure and temperature and selection of formation thermodynamic parameters of gas well were discussed at first.Based on the discussion and taking the measured data of well YS1 in Yaoyingtai Gas Field as example,two empirical formula methods were used to calculate the pressure and temperature under which the gas hydrate was formed in wellbore.On basis of distribution of pressure and temperature at different depth of wellbore and formation conditions of gas hydrate,it can be predicted whether hydrate is formed in wellbore at different flow rates so as to determine a minimum flow rate during production.For new well test,it can be predicted whether hydrate is formed in wellbore according to different production rate and wellhead pressure and temperature so as to formulate testing program and countermeasures in advance and avoid influence of ice barrier caused by hydrate formation on gas well test.