| As a clean energy,geothermal resources are regarded as one of the future energy development directions by countries around the world due to its huge reserves and wide distribution.According to its reservoir conditions,geothermal resources can be divided into hot dry rock and hydrothermal.Due to its huge theoretical reserves and considerable thermal output,hot dry rock geothermal resources have attracted government capital and social capital input in many countries for research and development,but the current development technology is still immature.Most areas in China are mainly based on hydrothermal geothermal resources,such as Yunnan Province and Sichuan Province.With the increased investment in improving air quality,the heating mode of coal-to-gas and coal-to-geothermal heating is rapidly expanding in North China,such as Xiong'an and Tianjin,indicating the spring of hydrothermal geothermal systems in the northern heating field has arrived.Tianjin is one of the regions that developed geothermal earlier in China,which is at the forefront of the country in terms of the number of geothermal wells,geothermal resource utilization,and geothermal heating area.However,early extensive development led to problems such as lower groundwater levels,lower hydrostatic pressure in the reservoir,and more difficult recharge.In view of these problems,it is urgent to carry out research work on sandstone reservoir water,heat conduction law and formation stress change law in the geothermal development site under well mining and irrigation mode to avoid problems such as excessive thermal breakthrough and land subsidence.In this paper,the sandstone-type thermal reservoir in the Panzhuang uplift structural area of Tianjin is taken as the research object.Based on the collected relevant geological,drilling,logging,and geological profile data,a three-dimensional geological solid model of the research area is established.The geothermal resource reserves were evaluated.Based on the analysis of the groundwater level drop and pressure drop in the actual project,and the analysis of the reservoir water-thermo-mechanical coupling process,a hydro-thermo-mechanical coupling model for the double well model in the study area is established,and the sensitivity analysis of the main factors of heat transfer and stress has been carried out.The research results provide some theoretical guidance for the development and utilization of hydrothermal geothermal resources in sandstone reservoirs in Tianjin.The following conclusions are drawn from the study:(1)GMS software is used to establish a three-dimensional geological entity of the reservoir based on information such as boreholes and geological sections;analysis of the geological entity constructed has found that it has a better control effect on the missing formations,and can characterize the striations at the fault.However,it cannot intuitively show the fault situation of the stratum.(2)Based on the established three-dimensional geological entity model,the thermal storage resources in the study area are estimated using Volume Method.Generally speaking,the thermal storage resources in the Panzhuang uplift structural area are abundant,equivalent to about 118.1×10~8t of standard coal;Wumishan Formation of Jixian(Jxw)is the dominant reservoir in the study area,and the proportion of thermal storage resources has reached about 50%.The thermal storage resources of Minghuazhen Formation(Nm)sandstone reservoirs are equivalent to 27×10~8t of standard coal,which is the second largest thermal reservoir.(3)Through analysis of factors such as flow rate,well spacing,opening length,and vertical distance of well bore,simulation studies on well production and irrigation under different schemes have been carried out.Under the condition that the physical parameters of the reservoir are not changed,the change in the upper pressure of the injection well and the production well is proportional to the flow rate and the well spacing.The increase in the flow rate and the well spacing less than 500 m results in a faster thermal breakthrough.In the open section length model,as the length increases,the pressure rise in the well decreases,which indicates that the pressure dissipation ability increases with the increase of the length of the well section,and it is recommended that it should not be less than 60m.(4)Porosity and permeability have a large impact on the water-conducting and heat-generating properties of the reservoir,and it has strong heterogeneity in the reservoir,showing a large uncertainty;well spacing and flow will affect the stress field near the mining well and injection well.As the flow rate increases,the stress on the overburden rock on the injection well and the mining well will increase,and the total displacement will increase.The maximum displacement can reach 8 cm in 50 years.Under the influence of thermal breakthrough,it is recommended that the well spacing should be controlled above 600m. |
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