Study On Heat Transfer Law And Heat Preservation Mechanism Of Dry Hot Rock Developed By U-shaped Well

As a clean,safe and efficient resource,hot dry rock is the key direction of our future energy development.Our resources of hot and dry rock are huge,but in the development and utilization aspect is still blank.At present,the dry hot rock development is basically carried out in the way of vertical well pattern fracturing in foreign countries.The cracks are fractured at the bottom of the well through hydraulic fracturing to construct a large fissure type geothermal energy system,which connects the injection well and the production well.However,this development mode has prominent defects,such as high water loss rate,rapid decay of thermal energy,easy to cause earthquakes and other problems.This paper proposes to carry out the leading research on heat extraction technology of dry hot rock U-shaped well,and discusses the way to develop dry hot rock in U-shaped well instead of artificial fracturing.A coupling model of unsteady flow heat transfer between U-shaped wellbore and dry hot rock reservoir was established,which was solved discretely by finite volume method combined with Crank Nicolson’s fully implicit scheme,and the reliability of the model was verified by experimental data from geothermal Wells.This paper studies the heat transfer law of dry hot rock exploited by U-shaped well,analyzes the temperature variation characteristics of wellbore and stratum in the process of exploitation of dry hot rock,discusses the heat transfer performance of U-shaped well under different slope and well type,analyzes the formation temperature distribution and heat extraction performance under two heat transfer boundary conditions,and simulates the heat transfer situation of U-shaped well under different concentration of nano-fluid.This paper studies the thermal insulation mechanism of dry hot rock developed in U-shaped well,determines the optimal thermal insulation depth after adding insulation layer according to the outlet temperature and heat taking power under different thermal insulation depth,and introduces several thermal insulation materials suitable for use in geothermal well.Under the condition of optimal insulation depth,the influence of different inlet temperature,injection flow rate and horizontal section length on U-shaped well outlet temperature and heat extraction power was quantitatively analyzed.The optimal heat extraction power parameter combination was obtained by orthogonal test method,and the factors affecting the heat extraction power were determined by variance analysis method.The research results further improve the theory of efficient heat extraction of dry-hot rock,which will provide reference for the development and utilization of dry-hot rock geothermal energy.