Research On Carbonate Rock Fracture Seepage And Heat Transfer Coupling Mechanism And Thermal Storage Production And Irrigation

In recent years,my country's new energy construction has developed rapidly.Under the general trend of the energy transition,the clean and efficient use of geothermal energy has been placed in a more prominent position.As one of the most high-quality geothermal fields,the carbonate geothermal field in Xiongxian County of North China has abundant geothermal resources,a large heat storage area,and a high heat recovery rate.Understanding the coupling mechanism of carbonate fracture seepage and heat transfer is of great significance for improving the heat recovery efficiency of carbonate reservoirs.However,due to the lack of understanding of the temperature distribution in the surface of the flowing fluid and internal fractures,an accurate understanding of the heat transfer characteristics of the rock fractures has not yet been achieved.This paper is based on the artificial reconstruction of carbonate thermal reservoirs under the background of my country's hydrothermal geothermal engineering,combined with the environmental characteristics of deep reservoirs with high temperature and in-situ stress.It adopts a self-developed real-time high-temperature conventional triaxial test system,which can truly simulate rock fractures.The natural convective heat transfer process,using a combination of experiment and simulation,to study the coupling mechanism of carbonate fracture seepage and heat transfer,combined with actual geothermal engineering to simulate the geothermal heat storage and mining recharge technology.The main work is as follows:(1)A ?50×100mm cylindrical carbonate rock was prepared,and its density and thermal conductivity were measured.XRD,SEM and 3D scanning analyzed the mineral composition.Using the real-time high-temperature conventional triaxial test system,we did a stable temperature of 70,90,110 ?,0,5,10,15 MPa confining pressure and 3,6,9,12,15,18ml/min flow rate convection heat transfer test.The inlet and outlet water temperature and the inner wall temperature of the fracture were obtained,and the heat transfer performance of the carbonate rock fracture was studied;(2)Based on the test data,the previous calculation formulas were compared and verified,and new calculation formula of convective heat transfer coefficient was proposed.The new formula derived was used to systematically analyze the influence of roughness,temperature,flow rate and confining pressure on the convective heat transfer characteristics of a single fracture in carbonate rock;(3)The COMSOL Multiphysics software was used to establish a numerical model of the heat transfer in a single fracture,and then the heat transfer process of a single fracture in a carbonate rock was simulated and calculated.A method of determining model parameters based on experimental data was put forward,and convective heat transfer simulation analysis under different environmental conditions was carried out.Experimental results verified the correctness and reliability of the numerical simulation,and obtained the evolution law of the reservoir temperature field;(4)An overall model of caprock-thermal storage-bedrock describing the thermal compensation process and the geothermal mining process was established.Using the "one extraction,one irrigation" injection-production mode for wells,the long-term operation process of geothermal wells with different well spacings was simulated,and the influence of the reinjection process on the thermal breakthrough of mining wells was studied.