Study On Influencing Factors And Prediction Of Output Temperature In Wellbore Heat-exchange Geothermal Well

With the gradual depletion of traditional resources such as oil and coal,and the improvement of environmental requirements,development of new green energy is becoming more and more urgent.Geothermal energy is a new kind of green,clean and renewable energy.It has been more and more popular for the rational development and utilization of geothermal resources.Geothermal mining methods can be divided into fluid heat-exchange and wellbore heat-exchange.Fluid exchange geothermal wells inject fluid into the formation,through the exchange of fluid and heat exchange from the production wells for geothermal mining;wellbore heat-exchange geothermal wells fluid does not enter the formation,through the wellbore heat-exchange.In the wellbore heat-exchange geothermal well oil casing is used as a concentric tube,and a heat insulation layer is added between the oil pipe sleeves.Fluid exchange geothermal well is difficult to recharge fluid and has pollution problems.Due to the fact that the wellbore heat-exchange geothermal well does not exchange fluid with the formation,it is not difficult to recharge fluid and also has no formation pollution.The output temperature of geothermal well is affected by many parameters,such as formation parameters,production performance and wellbore structure.This paper established a variety of wellbore heat exchange type geothermal well model using the CMG software,mainly including vertical concentric tube heat-exchange wells and horizontal section concentric tube heat exchanger type well,injected fluid flow process in geothermal well concentric tube is simulated,get the wellbore temperature and output temperature,and also described the radial formation temperature field.On the basis of this discussed injection parameters,formation parameters and wellbore parameters effects on the output fluid temperature and formation temperature field.The regression relationship between the output temperature and the main control parameters of the wellbore heat-exchange geothermal well is established by using the multiple nonlinear regression method.The output temperature prediction model has been put forward.The research results show that the injection rate,injection temperature,temperature gradient,vertical shaft depth and the thickness of insulation layer is the main controlling factors of output fluid temperature,the higher the injection rate is,the lower the output temperature is.The higher the geothermal gradient is,the higher the output temperature is.The higher the vertical depth is,the higher the output temperature is.The output temperature prediction model can accurately predict the output fluid temperature under different conditions,and the regression coefficient is close to one,so the model has good fitting accuracy.Based on influencing factor analysis and regression prediction discuss the way to improve heat-exchange effect,including injection mode change,intermittent mining and multi well with mining.The results show that the fluid circulation model that through casing injection and tubing production is reasonable.Intermittent mining and multi well mining can effectively improve the heat-exchange rate of wellbore heat-exchange geothermal wells,thus increasing economic benefits.