| Today,with the rapid development of world,the demand for energy is gradually increasing,and the use of fossil fuels will cause the greenhouse effect and environmental pollution increasingly aggravating.Therefore,in recent years,most countries in the world have adjusted energy structure and increased the proportion of clean and renewable energy in the total energy consumption.As a big coal consumer,China is also gradually optimizing energy structure.Geothermal energy,as a renewable green energy,has the advantages of huge reserves,wide distribution,stability and cleanliness,so it gradually gained people's attention.As a new geothermal resource,supercritical geothermal system has the characteristics of high enthalpy and mobility compared with traditional geothermal system.Therefore,it has attracted most countries and scholars in the world to conduct research in this field.At present,several projects have carried out or planned to carry out the development of supercritical geothermal resource around the world.The development of supercritical geothermal resource is related to the development and utilization of important national strategic resources and clean energy.However,the development of supercritical geothermal resources in the world is only in the exploratory stage,and the mechanism of multiphase fluid hydrothermal transport in the system is still unclear.Therefore,this article focuses on the key scientific problem of hydrothermal transport characteristics in the development of supercritical geothermal,based on the supercritical geothermal project of Iceland IDDP-2,by means of data collection,parameter identification and numerical simulation.And establish a three-dimensional supercritical geothermal system wellbore-reservoir coupling model on the actual site,with the data of injection test to identify reservoir parameters,determine the best development layer,and analyze the law of hydrothermal transport of multiphase flow in supercritical mining and the phase change phenomenon of wellbore.Provide an effective method for future Reykjanes geothermal field supercritical geothermal development productivity optimization,reservoir and wellbore hydrothermal evolution characteristics.In this paper,based on the IDDP-2 well of Reykjanes geothermal field in Iceland,the regional geological survey was collected to carry out numerical simulation study.Based on the injection test of IDDP-2 well,identifying the key parameters of reservoir.The identified three layers of reservoir permeability are:400?800 m D,2 m D,2 m D.The reservoir with higher permeability is determined as the development layer,and combined with IDDP-2 well,a supercritical duble well-reservoir coupling numerical model is established to study the mechanism of hydrothermal transport and phase change.The study found that in the initial stage(the first three years),the fluid in the production well is supercritical and gas phase,and the production temperature was stable;then there was a steep drop,a phase change phenomenon occurred in the wellbore,and the fluid was a supercritical and gas-liquid mixed phase;As the system runs,the final fluid is a liquid and gas-liquid mixed phase.There are two phases in which the temperature of the production fluid decreases rapidly:in the first phase,the fluid undergoes a"phase change"phenomenon in the wellbore,and the temperature drops sharply;in the second phase,the fluid flows toward the production wellhead in a gas-liquid mixture,and the temperature-pressure curve It evolves along the phase transition line,and the temperature of the upper part of the wellbore drops faster than that of the lower part of the wellbore.The supercritical geothermal system has a huge productivity advantage over the normal temperature geothermal system(reservoir temperature 428.5?).Under the condition of only changing the temperature of reservoir,the heat extraction efficiency is twice as high as that of normal temperature geothermal resources(reservoir temperature 300?).Comprehensively considering power generation efficiency and energy loss,from the perspective of energy efficiency,the supercritical geothermal system has higher wellhead pressure,increased pump energy consumption,and lower energy efficiency than normal temperature geothermal systems.However,as the system runs,it gradually increases,and in terms of heat extraction efficiency,it has greater development and utilization value.In addition,the method of reducing the pressure of the production well and increasing the roughness of the wellbore can be used to reduce the energy consumption.This paper provides a development scheme for the geothermal engineering of IDDP-2 well in the future,and analyzes the effects of rejection temperature,production and injection rate,well spacing,wellbore roughness and the mode of more injection and less production on hydrothermal output.After the comprehensive analysis of heat extraction efficiency,power generation efficiency and energy efficiency,the variable parameters of engineering are optimized.When the rejection rate is 76 kg/s and the production rate is 60 kg/s,it can effectively avoid the problem of reservoir damage caused by the high bottom hole pressure,realize the long-term stability of reservoir pressure.The increase of wellbore roughness can reduce the energy consumption of wellhead pump in producing Wells.With the decrease of rejection temperature and the increase of well spacing,the thermal extraction efficiency will increase.In this study,the optimal rejection temperature is 50?,the well spacing was 1000 m,and the wellbore roughness is 1×10-4.The corresponding optimal heat extraction efficiency,power generation efficiency and energy efficiency are 85.82 MW,32.43 MW and 37.1,respectively. |
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