Research On The Prediction Method And Optimization Of EGS Productivity And Longevity Based On Flow Field Splitting

With the rapid development of society,the demand for energy continues to increase,and conventional fossil energy sources will also cause carbon emissions to increase.At the same time,the shortage of conventional fossil energy has brought about a shift in the energy structure.Clean and sustainable energy utilization is the only way for future energy development.As an efficient and clean energy source,underground thermal energy determines its important proportion in the future energy structure.Among them,hot dry rock resources are important energy sources that can be used for social production.Its high temperature and large reserves determine that it will inevitably become one of the important energy sources in the future.In terms of underground thermal energy utilization,our country is keeping up with the times,and the efficient use of dry hot rock resources is also constantly being explored.Vigorously developing hot dry rock resources is an important way to achieve my country’s "carbon neutral" goal.As an effective means to develop medium and deep high temperature dry hot rock resources for power generation,the Enhanced Geothermal System(EGS)has received more and more attention.Faced with huge reserves of hot dry rock resources and advantages in environmental protection,EGS mining technology also needs to be strengthened accordingly.But now EGS is in its infancy,and there are few ideal EGS practical projects suitable for commercial promotion.In addition to the technical limitations of thermal storage transformation,the inaccurate prediction of heat production and operating longevity of EGS is an important reason that restricts the rapid popularization of EGS practical projects.Unclear and inaccurate influencing factors of EGS thermal recovery,and unclear flow law of the flow field in the thermal storage are the fundamental reasons for the inaccurate prediction of EGS production capacity and operating longevity.In this paper,in order to solve the problem of predicting the production capacity and longevity of EGS,the EGS production capacity and longevity control equation is established based on the Dupuit formula and the heat absorption and release formula.Analyze the seepage field and heat transfer law in the EGS thermal storage,and establish the EGS productivity and longevity prediction formula,and conduct application research and optimization on it.The main research contents are as follows:(1)According to the characteristics of the EGS thermal storage,the thermal storage is simplified to a homogeneous porous medium model,the EGS heat transfer process is analyzed,and the permeability is used as the medium to simplify the EGS complex multi-field coupling process into a flow-heat(TH)coupling process.Derive EGS productivity and longevity control equations,and propose important parameters for EGS productivity and longevity calculations.Based on the principle of complex potential function and pressure superposition,the potential function and flow function of multiple plane well layout methods are derived respectively,and the pressure potential and flow field distribution laws of different well layout methods are calculated.The idea of "the flow field splitting method of dividing the control area of a single injection well based on the flow field distribution law,and simplifying the multi-wells EGS to multiple double-wells EGS to calculate the productivity and longevity separately" is proposed.(2)Based on the EGS productivity and longevity control equations and the EGS flow-heat coupling mathematical model,the factors affecting the important parameters in the control equations are analyzed.Designed and built a miniature seepage heat transfer model experimental system,carried out miniature seepage heat transfer experimental research,obtained the water temperature and the temperature response law of the rock mass,and verified the accuracy of the flow-heat coupled numerical simulation.Carry out the double-wells EGS seepage heat transfer numerical simulation experiment under actual working conditions,analyze the influence of each influencing factor on important parameters,modify the important parameter influence factors,and obtain the double-wells EGS productivity and longevity prediction formula.(3)Study the pressure potential and flow field distribution of different well layout methods,and calculate the minimum pressure coordinate between the two injection wells.A method for splitting the flow field of the planar multi-wells EGS is proposed:splitting along the angle bisector formed by the connecting line of adjacent injection wells and production wells to obtain the control area of a single injection well.The hydropower comparison instrument is improved,carried out multi-wells hydropower comparison experiments,analyzed the pressure potential distribution law in the flow field,and qualitatively verified the EGS flow field splitting method.Based on Darcy’s law,a plane multi-wells flow field finite element numerical simulation is carried out,and the pressure potential and velocity distribution law in the flow field are analyzed,and the EGS flow field splitting method is quantitatively verified.(4)Based on the principle of complex potential function and pressure potential superposition,the flow reduction mechanism of multi-wells plane flow field after pressure potential superposition is analyzed,the flow rate reduction experiment system is developed,and the multi-wells pressure superposition experiment is carried out to verify the correctness of the plane flow reduction mechanism.Carry out multi-wells integral EGS finite element numerical simulation and double-wells EGS finite element numerical simulation after splitting to analyze the influence of the number of wells and flow reduction on EGS productivity and longevity.Based on the double-wells EGS productivity and longevity prediction formula,the key parameters in the EGS productivity and longevity control equation were revised,and the multi-wells EGS productivity and longevity prediction formula is proposed.(5)The EGS productivity and longevity prediction formulas are compared with existing literature cases to verify the correctness of the double-wells and multi-wells EGS productivity and longevity control equations.Relying on the Tengchong Rehai Geothermal Field in Yunnan,and based on the EGS productivity and longevity prediction formula,carry out the EGS productivity and longevity prediction of different well layout methods,and analyze the EGS productivity and longevity of different well layout methods.An optimization method for the application of EGS productivity and longevity prediction formulas is proposed.