Theoretical And Experimental Study On Hydrothermal Geothermal Sustainable Heat Extraction Based On Multi-scale Entropy

The dual carbon target puts forward higher requirements for geothermal energy,which will bear a higher proportion of renewable energy in the future.In large-scale and long-term scale,flow,heat and ecological balance are the bottleneck problems to be solved to improve the proportion of geothermal energy.Geothermal reservoir prediction and efficient heat extraction are important links in the sustainable utilization of geothermal energy.Due to the complexity and heterogeneity of geology,it is difficult to directly predict the supply,discharge and runoff of geothermal resources in the targeted area during geothermal dynamic operation,and the efficiency of existing heat extraction technologies is low.Entropy measurement is a useful tool to reveal the complexity of dynamic system.In this study,entropy measurement method is applied to the dynamic prediction of geothermal reservoir.By analyzing the multi-scale entropy of dynamic differential pressure signal,we try to find the orderly transformation law of geothermal reservoir supply,discharge and pumping irrigation in the dynamic operation of geothermal reservoir.Aiming at the problem of low heat extraction efficiency of recirculating wells,the leaky downhole coaxial open loop geothermal system is proposed,and the thermal performance optimization and thermal economy analysis are carried out.In order to ensure the economic and sustainable utilization of geothermal resources,research should be carried out from four aspects: dynamic prediction of geothermal resources,evaluation of key physical parameters,optimization of thermal performance of heat extraction system and economic analysis.Firstly,the application of information thermodynamic entropy from micro system to macro system is combed,and the generalized thermodynamic entropy is proposed to measure the order degree of nonlinear system.The analysis shows that the differential pressure signal of the system contains a large amount of flow information,which is easy to obtain,and is suitable for revealing the entropy measure signal of the dynamic nonlinear system of heat storage operation.The sand box test-bed is built to obtain the differential pressure signal and temperature signal under different heat storage supply boundary conditions.The multi-scale entropy of the system differential pressure signal under different boundary modes is extracted to characterize the nonlinear dynamic characteristics of different modes.Taking the scale entropy increase rate and the 30 th scale entropy under different supply boundary modes as eigenvalues,the classification prediction model is built by support vector mechanism,and the prediction accuracy of the model is as high as 90.70%.Secondly,aiming at the shortcomings of geothermal parameter evaluation methods,an analytical model of the leaky downhole coaxial open loop geothermal system is proposed,and a nonlinear optimization model of aquifer thermophysical and hydraulic parameters is constructed based on the analytical model.Through improved genetic algorithm and sand box experimental data inversion,important physical parameters such as aquifer specific heat capacity,thermal conductivity and permeability coefficient are obtained with high accuracy,It provides a basis for the research of the leaky downhole coaxial open loop geothermal system.Then,the numerical simulation of a heating cycle(120 days)is carried out for the leaky downhole coaxial open loop geothermal system.The thermal performance of various influencing factors is analyzed,and the critical Rayleigh number of overflow aquifer is obtained.Based on this,the thermal performance optimization correlation is constructed,which can provide theoretical guidance for engineering design.Through sensitivity analysis,it is found that the heat transfer performance is most sensitive to the permeability of aquitard,the thickness of aquitard,pumping and irrigation flow and injection temperature.When the permeability of aquifer and aquitard is greater than or equal to 100 and the radius of aquitard is greater than or equal to the heat influence radius,thermal penetration can be effectively avoided.Under the benchmark working condition,the thermal influence radius of wellbore and soil is less than 3 m,the thermal influence radius of aquifer is about 28 m,and The thickness of aquitard is more than 15 m,indicating that the heat of aquifer plays a major contribution to the leaky downhole coaxial open loop geothermal system.When the water resisting performance of the aquitard is good,the injection temperature can be lower than 20 °C,and the pumping and irrigation flow is recommended to use large flow without damaging hydraulic fracturing.Finally,aiming at a variety of uncertain factors of geothermal,a thermal economic optimization model is constructed to provide an effective reference for geothermal economic evaluation.The research shows that the investment payback period of the leaky downhole coaxial open loop geothermal system is 7 years.The probability density of net operating value in 30 years is analyzed.The net operating value in the 10 th,15th,20 th,25th and 30 th years is greater than 2.07,5.35,8.99,13.05 and 17.89 million respectively with a probability of 99.9%.It shows that the leaky downhole coaxial open loop geothermal system heating technology has good economy and is worthy of large-scale popularization.