Construction Of Thermal Conductivity Model And Analysis Of Dynamic Characteristics During Deep Geothermal Reservoir Mining

With the decline of traditional energy reserves,geothermal energy,as a safe,reliable,clean and low-carbon renewable energy with large storage capacity,has attracted extensive attention.In the exploitation and utilization of geothermal energy,fine exploration,effective heat extraction,natural recovery and other key issues are affected and restricted by the heat transfer process of geothermal reservoirs.The construction of more accurate static heat transfer(thermal conductivity)analysis model of porous media for geothermal reservoir plays a theoretical supporting role in fine exploration,effective heat capture and natural recovery of geothermal application process.At present,the research on the mechanism of geothermal reservoir and heat transfer is mostly analyzed through experiments,geotechnical physical properties and geotechnical structure in microscopic aspects.Macroscopically,geothermal reservoirs are divided into hydrothermal type,shallow layer and dry hot rock.There are many deficiencies in the description and analysis model,which are not enough to analyze the geothermal exploitation process in detail.In this paper,the exploitation process of deep geothermal reservoir is studied.By introducing the theory of heat and mass transfer in porous media,the physical model of dynamic characteristics of the exploitation process of deep geothermal reservoir is established according to the geological characteristics of geothermal reservoir.The geothermal reservoir in the development process is horizontally divided into the original area at infinity,the development area near the hot well and the fluctuation area affected by the two.Based on the REV(Representative Elementary Volume)characterization method,the REV description method for porous media of deep geothermal reservoir was established.The characterization and analysis of the deep geothermal reservoir are carried out,and the related description parameters of the geothermal reservoir are given,including basic parameters such as porosity,pore impurity and pore water content.The cross-scale modeling method is analyzed,and an analytical method connecting local and whole is proposed.Based on the analysis of karst geothermal reservoir and sedimentary geothermal reservoir,porous media can be divided into pore type and bedding type according to the structural characteristics of porous media.The static heat transfer analysis model of layered structure geothermal reservoir is established for layered porous media.At the same time,the analysis process and action mechanism of the two models are further discussed.1.For the static heat transfer analysis model of pore structure geothermal reservoir,taking granite as an example,the application analysis based on numerical calculation shows that the model can be flexibly applied in three intervals of geothermal reservoir development process,and the three intervals are all affected by porosity.The microscopic composition of the original zone is relatively stable,and the influence of impurity content and pore water content on thermal conductivity can be ignored.In development zone and fluctuation zone,the influence of impurity rate and pore water content should also be considered.2.For the static heat transfer analysis model of stratified structure geothermal reservoir,taking sandstone as an example,the application analysis based on numerical calculation shows that the thermal conductivity of original area,development area and fluctuation area all shows a decreasing trend with the increase of porosity.The third interval increases with the influence of the impurity content,and the growth rate increases with the increase of the porosity.The thermal conductivity of the development area increases obviously with the increase of pore water content,and the change rate increases with the increase of porosity.The fluctuation area is less affected by pore water content and the variation range is not as obvious as the development area.The thermal conductivity of the original area,development area and fluctuation area increases with the increase of tortuosity and pore channel distribution coefficient.With the increase of the interval influence coefficient,the thermal conductivity in the fluctuation area shows an upward trend.