Multi-field Coupling THM Process In Carbonate Reservoirs And Numerical Simulation

In recent years,China attaches great importance to carbon emission reduction.In2021,the two sessions will write carbon peak and carbon neutral into the government work report for the first time.Geothermal energy has been vigorously developed and utilized as a clean,environmentally friendly and renewable energy source.It is expected to play an important role in helping my country achieve its carbon peak by 2030 and carbon neutrality by 2060.An important part of geothermal development is geothermal reinjection,which can effectively deal with geothermal tail water and maintain thermal storage pressure.However,the temperature of reinjection tail water is usually low,which will lead to the decrease of reservoir temperature and even thermal breakthrough.Geothermal reinjection involves a complex process of multi-physical coupling of seepage field,temperature field and stress field.Therefore,the study of thermal-hydro-mechanical coupling process is an important basis for evaluating production efficiency,predicting the thermal breakthrough time of pumping wells,and optimizing the design of extraction and irrigation schemes.Geothermal development usually focuses on the well production and irrigation system.With the large-scale development,the multiple well system is gradually formed.It is of great significance to carry out the research on the small-scale and large-scale of geothermal wells for the actual thermal storage and reinjection project.In this thesis,by means of reinjection tracer test,theoretical analysis and numerical simulation,different scale studies from geothermal wells to multiple well system are carried out to reveal the thermal-hydro-mechanical coupling of thermal reservoir under the condition of low temperature tail water reinjection,and to clarify the dynamic response process of temperature field of carbonate thermal reservoir under well production and irrigation in the study area,In order to provide scientific support for the large-scale development of geothermal resources,the influence of different mining and irrigation schemes on the temperature field of geothermal field is predicted and analyzed.The main conclusions are as follows:(1)The low temperature tail water reinjection leads to the coupling process of hot water and power in carbonate reservoir.The low temperature tail water reinjection into the reservoir changes the reservoir stress and displaces the reservoir rock mass.At the initial stage of operation,the reservoir pressure,fracture opening,permeability and flow velocity on the reinjection side increase significantly,and the convective heat transfer effect is obvious,and the reservoir temperature decreases rapidly.The decrease of reservoir temperature and the shrinkage deformation of rock mass also lead to the increase of fracture opening.With the long-term operation of the production and irrigation system,the reservoir temperature and pressure gradually tend to be stable,and the variation range of reservoir permeability decreases.The reinjection pressure and temperature are important factors that affect the temperature of heat storage.(2)The quantity of water production is an important factor to maintain the long-term performance of thermal storage.Increasing the production and irrigation quantity will accelerate the cold front migration,and make the thermal breakthrough time of the well advance.The time of thermal breakthrough can be prolonged by reinjection deeper than the mining depth.When the geothermal development is large,there are many geothermal wells,and there will be mutual influence among different wells,and obvious cluster effect will occur.(3)The expansion of the interval between wells can effectively delay the thermal breakthrough of the well and maintain the stability of the reservoir temperature.On the surface of simulation results,the interval between wells is more than 500 m,which can obviously extend the thermal breakthrough time of the well.