| The development and utilization of traditional fossil energy sources have made the greenhouse effect increase seriously,and the exploration and development of new energy sources have become a breakthrough for the development of an environmentfriendly society and an important development path to achieve the great goal of carbon neutrality in China.Currently,new energy sources are increasingly to replace conventional fossil fuels since they have large and wide reserves as well as high energy utilization rates.Nuclear,wind,clathrate hydrate and other new forms of energy have the advantages of vast reserves and high efficient energy use,and are gradually replacing traditional fossil fuels.However,uranium ore and natural gas hydrate are mostly located in loose and broken strata with high water content and poor stability,which are prone to core dropping or pressure-holding failure by conventional drilling methods,resulting in low core extraction rate and the problems of low face-in efficiency and long drilling cycle,which seriously restrict the development and utilization of new energy sources.The emergence of ice coring technology provides a new possibility to solve the above problems.The formation does not require complicated mechanical parts in the drilling tool,the pressure-retaining capacity of the ice valve at 78 mm height is up to 58 MPa,which is several times of the drilling coring requirement and is expected to be a new type of drilling coring means.Therefore,combining the law of heat transfer and refrigeration mechanism to reveal the growth characteristics of the ice valve provides a reference for optimizing the heat transfer structure of the ice valve tube,improving the growth rate of the ice valve and shortening the formation time of the ice valve,which has important guiding significance for the performance optimization of the ice coring apparatus.Based on the above-mentioned problems and the actual engineering needs,this paper carries out research on the optimization of ice valve growth rate through a combination of theoretical research,numerical simulation,and simulation tests,and the specific research contents and conclusions are as follows.(1)Analyze the complex formations and evaluation of particle composition of the core samples,particle gradation,and cementation capacity,and two different new ice seal corers are proposed and designed.The inner-plane structure ice-sealed coring device is suitable for the formation with small particle size,loose and weak cementation or even non-cementation,finally,in the ice valve pipe,the bottom sample is completely frozen and then the drilling is carried out,after the core is clipped,the brush of the natural convection blocking device between the inner and outer tubes rebounds,which accelerates the freezing process of the fluid at the bottom of the ice valve tube and shortens the freezing time.(2)The relationship between the thermal conductivity of the wall material of the ice valve tube and the ice valve formation rate was analyzed,and the temperature variation curves of the monitoring points in the model were obtained.Build the simulation test equipment,carry out the test and obtain the key data,the test data and simulation data comparison and analysis.The results show that there is a great difference between the growth rate of pure water ice valve and ice rock composite valve and the thermal conductivity of the ice valve tube.The difference of thermal conductivity between different materials is 24 times,but the thickness of thermal coupling wall of ice valve tube is only 2mm,which can not play a key role in increasing the cold transfer At the later stage of ice valve growth,the main medium of cold energy transfer changes,and the ratio of cold energy to internal energy and phase change energy increases,which further reduces the cold energy transfer efficiency.The growth rate of pure water ice valve increases by 5.2% under different conditions,the growth rate of ice-rock composite valve increased by 6.7%.(3)To accelerate the fluid freezing process at the bottom of ice valve tube,a natural convection blocking device is proposed.In order to study the relationship between the natural convection intensity and the growth rate of ice valve,the natural convection was analyzed based on the Boussinesq hypothesis,the brush arranged in a matrix and the fluid in the region are abstracted into a porous medium model.The effect of natural convection on the growth of ice valve is evaluated based on the temperature monitoring data of horizontal and vertical distribution,and the cloud images of temperature and solid-liquid phase.The results show that the natural convection intensity is the key factor affecting the growth rate of ice valve for pure water and sea water,the growth rates of pure water ice valve and sea ice valve were 19.6%,24.5% and 28.5%,21.8%,28.1% and 34.3%,respectively.In the direction of gravity,the growth rate of ice valve is greatly affected,while in the radial direction,it has little influence.(4)The different structure of evaporation cavity in ice valve tube is studied.The evaporative cavity models with 150 mm height were established,and the evaporative phase transition was simulated to reveal the evaporative law of refrigerant.The results show that the liquid refrigerant tends to diffuse horizontally under the influence of gravity,while the gas refrigerant tends to move toward the outlet side under the influence of pressure.The temperature distribution on the wall of the evaporator is uneven,and the maximum temperature difference is about 5 ° C.The refrigerant in the spiral groove evaporating chamber is drained by the spiral channel,and evaporates fully along the outer wall under the action of centrifugal force.The spiral groove structure can reduce the disturbance and turbulence in the evaporation chamber,reduce the eccentricity in the freezing process,and shorten the ice valve formation time by 2 min.(5)To verify the numerical simulation results,experimental observation was carried out to study the effect of different structure of evaporation chamber on the growth of ice valve.According to the Comprehensive Evaluation and analysis,the height of evaporation chamber and the evaporation efficiency of refrigerant can affect the growth of ice valve,the temperature change law of the monitoring point is in good agreement with the numerical simulation results.The spiral groove structure can effectively improve the refrigerant evaporation efficiency,homogenize the temperature distribution in the evaporation chamber,reduce the temperature difference on the opposite side,and reduce the eccentricity of ice valve growth.The height of evaporating cavity was positively correlated with the evaporating efficiency of refrigerant in different cavities.When the height of evaporating cavity was shortened to 50 mm,the eccentricity of the ice valve obtained from the structure of the tube-type evaporating cavity decreased obviously.(6)Based on the above research results,the material,structure and dimension parameters of the ice valve pipe are optimized comprehensively according to the drilling condition of sandstone uranium deposit,a new type of ice-sealed coring device at the bottom of hole was used to test the coring performance.The results show that the evaluation criteria of parameters obtained by numerical simulation and simulation test play a key role in the optimization of ice valve pipe in ice-sealed coring device.The theory of optimizing the growth rate of ice valve based on the heat transfer and refrigeration theory has been verified in the coring test.The optimized structure of the ice valve tube is Φ62MM in diameter and 40 mm in height of the evaporation chamber.A complete ice-rock composite valve can be obtained in the ice valve tube within 30 min to meet the requirement of supporting the samples in the core tube,the coring rate is more than 90%,which can meet the actual performance requirements of the project and lay a foundation for the application of the new type of ice-sealed coring device. |
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