Model Study On Temperature Field Distribution Of Offshore Gas Hydrate Production Wells

Hydrate production wells are different from conventional production wells in that there is a phase transition process of hydrate in the production process,and the secondary generation of hydrate is easy to occur in the wellbore during the production process,which will cause the wellbore temperature field distribution of hydrate production wells to be significantly different from conventional production wells,In addition,when the heat injection method is used to develop hydrate reservoirs,there are thermal fluids with opposite flow directions in the wellbore,which makes the heat transfer process of hydrate production wells more complicated than that of conventional production wells.In order to accurately describe the wellbore temperature distribution of offshore hydrate production wells and realize the prediction of hydrate production area,it is necessary to calculate the accurate wellbore pressure distribution.Therefore,the kinetic model and deposition rate model of hydrate are established in this thesis,and a pressure distribution model of hydrate production wells considering hydrate growth and deposition is established on this basis.After realizing the accurate calculation of wellbore pressure distribution,the phase transition heat model of hydrate was established,and on this basis,a wellbore temperature distribution model for hydrate production wells,which takes into account the effects of hydrate phase transition,frictional heat generation,and countercurrent heat transfer,is established under depressurized mining and hot water injection mining methods,and proposed a new iterative solution method.Considering the interaction between wellbore temperature and pressure,a coupled calculation method of wellbore temperature and pressure for offshore hydrate production wells was proposed and a C# program was compiled to solve it.The calculation results of the model were compared with actual production data and commercial software WELLFLO to confirm the accuracy of the model.The sensitivity analysis of the influencing factors such as production rate,injection temperature,injection pressure and injection volume is carried out in this thesis.The results show that water-gas ratio and injection temperature have significant effects on wellbore temperature distribution.An example calculation of an offshore hydrate production well was carried out by using the developed software "Software for Calculation of Wellbore Temperature and Pressure of Offshore Hydrate Production Wells and Prediction of Hydrate Generation Area".The calculation results show that under the conditions of the example,the hydrate generation area of the heat injection method is significantly smaller than that of the depressurization production,which significantly improves the wellbore flow state of the hydrate well.This study can realize accurate prediction of wellbore temperature distribution of offshore hydrate production wells and early warning of hydrate formation risk,which has guiding significance for wellbore temperature prediction on site,production management of hydrate wells and prevention of secondary gas hydrate formation.