Numerical Simulation And Analysis Of Wellbore Temperature In Geothermal Wells By Coupling Drilling Fluid Temperature Characteristics

Geothermal energy has a broad development prospect as a green,high-efficiency huge-reserves and renewable new energy.The development and utilization of geothermal energy depend on drilling work,and the geothermal wells formation temperature is high,which affects the characteristics of the drilling fluid,and the characteristics of the drilling fluid determine the wellbore temperature.In addition,the geothermal wells often have multiple geothermal gradients.In this paper,the temperature of the geothermal wells was simulated and analyzed by coupling drilling fluid temperature characteristics and considering the influence of multiple geothermal gradients in the calculation.It is very important to calculate the temperature of the wellbore accurately.The results of this paper are as follows:1.The heat transfer models of the wellbore under the circulation condition was established.According to the energy conservation theorem and the basic principles of heat transfer and combined with the actual situation of the wellbore,the steady-state heat transfer model and the unsteady heat transfer model of the wellbore under the circulation condition were established and solved.2.The temperature characteristics of drilling fluid were studied.The effects of temperature on drilling fluid density,flow rate,specific heat capacity,thermal conductivity and viscosity were studied.3.The accuracy of the heat transfer models of the wellbore under the circulation condition was evaluated.The accuracy of the steady state heat transfer model,the unsteady heat transfer model with constant drilling fluid characteristics and the unsteady heat transfer model by coupling drilling fluid temperature characteristics under the circulation condition was evaluated.It is concluded that,for the wellbore studied,the steady state heat transfer model,the unsteady heat transfer model with constant drilling fluid characteristics and the unsteady heat transfer model by coupling drilling fluid temperature characteristics have good accuracy,and the unsteady heat transfer model by coupling drilling fluid temperature characteristics is the most accurate.4.The unsteady heat transfer model by coupling drilling fluid temperature characteristics was applied.The unsteady heat transfer model by coupling drilling fluid temperature characteristics was applied to the study of the temperature of the Yangyi ZK212 geothermal well and the Qinghai Guide ZR1 geothermal well and the influence of multiple geothermal gradients were considered in the calculation.The model had good applicability.5.The sensitivity of the parameters was analyzed.The wellbore temperature of the Yangyi ZK212 geothermal well was re-simulated by changing the geothermal gradient,the volume flow rate of the drilling fluid,the inlet temperature,the cycle time,the annulus clearance,the density of the drilling fluid,the specific heat capacity of the drilling fluid,the thermal conductivity of the drilling fluid and the viscosity of the drilling fluid and the results were compared with before the change.The influence of the above parameters on the wellbore temperature of the Yangyi ZK212 geothermal well was analyzed.Then the conclusions of the sensitivity analysis of this paper were compared with the conclusion in the predecessors' articles.