Study On Influencing Factors And System Optimization Layout Of Pumping And Injection Effect Of Mid-deep Geothermal Resources In Meixian City

As a renewable and clean energy,geothermal energy is of positive significance to the realization of the goal of carbon peaking and carbon neutrality,among which the middle and deep geothermal energy with great potential for development has attracted wide attention.Located in Guanzhong Basin,Meixian County has abundant geothermal resources and great potential for development.However,its research degree is relatively low.This paper carries out numerical simulation research on mid-deep geothermal energy in Meixian urban area,and the main research contents are as follows:The water-thermal coupling model of the study area was constructed to optimize the design of geothermal resource pumping and injection scheme.The influence of design and operation parameters of geothermal pumping and injection system and thermal reservoir parameters on the effect of pumping and injection was analyzed.Different pumping and injection conditions were designed to simulate,and the optimal pumping and injection scheme of geothermal well in the study area was simulated and predicted.The main research results are as follows:(1)The reasonable distance between pumping and injection wells in upstream recharge is200～300 m,and that for downstream recharge is 150～300 m.Upstream recharge is recommended when the design distance of pumping and injection wells is between 200 and 300m.Without considering the influence of downstream recharge on downstream geothermal resources,the design distance of pumping and injection wells is between 150 and 200 m,so downstream recharge is recommended.(2)The Lantian-Bahe Formation thermal reservoir and weathered fissure zone thermal reservoir are jointly developed.This development model has high geothermal quality,small variation of geothermal system head and slow decrease of thermal reservoir temperature,so it is suggested to adopt the dual thermal reservoir development model.(3)The larger the flow rate of pumping and injection,the faster the temperature of thermal reservoir drops,and the greater the influence range of pumping and injection system on thermal reservoir temperature field.The lower the recharge temperature is,the faster the temperature of the thermal reservoir drops,and the larger the influence range of the pumping and injection system on the thermal reservoir temperature field is.The recommended flow rate of injection is 3000 m~3/d,and the recharge temperature is 15℃.(4)The larger the permeability coefficient is,the faster the temperature of the thermal reservoir drops,and the larger the influence range of the pumping and injection system on the thermal reservoir temperature field is.The smaller the porosity is,the faster the temperature of the thermal reservoir drops,and the larger the influence range of the pumping and injection system on the thermal reservoir temperature field is.The greater the thermal conductivity,the greater the influence range of pumping and injection system on thermal reservoir temperature field.The smaller the volume heat capacity is,the faster the temperature of the thermal reservoir drops,and the larger the influence range of the pumping and injection system on the thermal reservoir temperature field is.(5)The influence of continuous pumping and injection on the geothermal system is much greater than that of intermittent pumping and injection,and the thermal breakthrough phenomenon has occurred in the pumping wells of continuous pumping and injection during the 20-year operation period.After 20 years of operation of the pumping and injection system,if the life of the pumping and injection well is prolonged,there will be no thermal breakthrough phenomenon in the pumping well within a certain number of years(8 years).The geothermal system with one pumping and two injection systems can not only achieve the equal balance of pumping and injection,but also achieve better geothermal pumping and injection effect under this mode.The service life of the geothermal pumping and injection system is 33 years.(6)Through the optimization design of the pumping and injection scheme in the study area,the optimal scheme is determined to be the pumping and injection well matching mode(upstream recharge 250 m well distance).Under the optimal pumping and injection mode,no thermal breakthrough occurred in all pumping Wells in the study area during the 20-year operation period.During the pumping and injection cycle,the head of all pumping wells decreased slightly and the head recovered well.The upstream recharge mode with the distance of 250 m pumping and injection wells was suitable for the exploitation of geothermal water in the study area.