| Natural gas hydrate is a kind of clean energy with great development prospects.At present,the research on natural gas hydrate exploitation in China is at a critical stage.The thermal stimulation method is considered to be very effective,compared with other natural gas hydrate extraction methods,and the heat transfer characteristics of the thermal stimulation method are directly related to the temperature field distribution and effective thermal conductivities of hydrate-bearing sediments.Therefore,this study focuses on the effective thermal conductivities of hydrate-bearing sediments and the temperature field distribution of hydrate-bearing sediments during heat injection.First,the effective thermal conductivities of TBAB hydrate-bearing sediments and cyclopentane hydrate-bearing sediments under different temperatures,particle sizes and types of porous medium were measured by a probe-type thermal conductivity meter.The measurement results show that the effective thermal conductivities of the hydrate-bearing clay system has a weak positive correlation with temperature,while the effective thermal conductivity of the hydrate-bearing quartz sand system and the hydrate-bearing silicon carbide system have a weak negative correlation with temperature.The effective thermal conductivities of both TBAB hydrate-bearing sediments and cyclopentane hydratebearing sediments decreased with the increase of the particle size of quartz sand,and the effective thermal conductivity of cyclopentane hydrate-bearing sediments was larger.In addition,the effective thermal conductivity of hydrate-bearing sediments is greatly affected by the intrinsic thermal conductivity of porous media,and the effective thermal conductivities of hydrate-bearing sediments under different porous media systems are quite different.Among them,the effective thermal conductivity of the hydrate-bearing silicon carbide system is larger than that of the hydrate-bearing clay system,while the effective thermal conductivity of the hydrate-bearing quartz sand system is between the ones of these two systems.Then,a thermal infrared continuous temperature field measurement system for hydrate-bearing sediments was established,and the platform was used to directly and in situ perform thermal infrared imaging on the continuous temperature fields of hydratebearing sediments during electric heating and hot water injection,respectively.The obtained experimental data can comfirm the feasibility of the application of thermal infrared imaging technology on the hydrate research.Infrared thermal imaging technology was used to study the variation of the temperature field distribution of TBAB hydrate-bearing sediments under different TBAB solution concentrations,heating powers,water bath temperatures,particle sizes and types of porous media during electric heating.The experimental results show that when the concentration of TBAB decreases,the heating power increases,the temperature of the water bath increases,the particle size of the porous medium increases and the effective thermal conductivity of hydrate-bearing sediments decreases,the variation radius of the temperature field of the hydrate-bearing sediments is relatively larger.Infrared thermal imaging technology was also used to measure the temperature field distribution of TBAB hydrate-bearing sediments in the process of hot water injection.In addition,the effects of TBAB solution concentration,water injection flowrate,water injection temperature,water bath temperature,particle size of porous media and pipe structure on the temperature field distribution of hydrate-bearing sediments were investigated.The results show that the water injection flowrate increases,the water injection temperature increases,the water bath temperature increases,the particle size of the porous medium increases and the effective thermal conductivity of hydrate-bearing sediments decreases,the change radius of the temperature field of hydrate-bearing sediments increases,when the concentration of TBAB solution decreases.Finally,the numerical simulation of the temperature field distribution of hydratebearing sediments during the heat injection was carried out,and the effects of heat injection time,heat injection flowrate,heat injection temperature and porosity on the temperature field distribution of hydrate-bearing sediments are explored.The simulation results show that the heat injection flowrate has a significant impact on the temperature field distribution of the hydrate-bearing sediments.Meanwhile,the hydrate-bearing sediments with high porosity has a larger radius of variation of the temperature field during the heat injection process,which is relatively benefical to hydrate exploiration by heat injection. |
