Study On The Prediction Of Natural Gas Hydrate Based On Coupling Calculation Of Transient Temperature And Pressure In Well Bore Of Gas Well

During the production of gas wells,the formation of hydrates will destroy the normal operation of natural gas production and gathering process.It may lead to a shutdown or even a serious safety accident.Therefore,it is necessary to predict the conditions and position of hydrate in the wellbore scientifically,in order to provide a theoretical basis for the prevention and control of gas hydrate in gas field.The distribution of temperature and pressure of the wellbore must be obtained before predicting the formation of hydrates.However,some gas wells with complex well conditions can not be measured by pressure gauges or thermometers,and the temperature and pressure models commonly used are usually only applicable to steady state calculations.This paper extensively investigates the relevant literature on temperature,pressure and the prediction model of hydrate at home and abroad.Based on the physical model of the wellbore and the basic theory of heat transfer,the relevant parameters of the model are considered as variables.On the basis of the existing transient model,the paper considers the actual situation of the thermal conductivity of the casing with the change of temperature.A transient temperature model including coupling calculation of total thermal resistance and temperature in wellbore stratum composite medium system is established,combining with wellbore two-phase pressure model,temperature and pressure coupling calculation is carried out.In order to calculate the temperature and pressure conditions of hydrate formation,and get the corresponding depth,temperature and pressure value of the formation of hydrate in the wellbore.It is necessary to associate the calculation results of the temperature and pressure with the prediction model of the hydrate,and to write the above model into a calculation program.The comparison of calculation results,model verification and single factor sensitivity analysis show that:(1)Partial physical parameters in the temperature and pressure models vary greatly with the depth and time.If they are considered as a fixed value,the calculation results will have a larger deviation.(2)By comparing with commercial software,classical model and uncoupled model,the coupled model of temperature and pressure established in this paper has higher accuracy both in transient state and steady state,and it is quite different from the results calculated by uncoupled model.(3)Hydrate is more likely to generate in the early stage of gas well production.Therefore,the transient temperature and pressure coupling model established in this paper is more practical for predicting hydrate fonnation than the conventional steady state model.(4)Components of natural gas affects the formation of hydrates in the wellbore by changing the temperature and pressure needed to generate hydrates.Oil and casing materials,tubing size,gas production,water yield,fluid specific heat and thermal conductivity of cement ring mainly affect the formation of hydrate in wellbore by changing the temperature and pressure distribution of wellbore.(5)The formation of hydrates in the wellbore can be prevented by means of production controlling,optimization of oil and casing,and downhole throttling.