Study On Ex-situ Measurement Method Of Hydrate Thermal Conductivity

Natural gas hydrate is an ice-like clathrate compound formed by water molecules and gas molecules(mainly methane)under low temperature and high pressure conditions.It is widely distributed in permafrost and seafloor sediments on the continental margin.It is considered to be the 21st century One of the ideal new energy sources.Because the stability of natural gas hydrates is sensitive to temperature changes,when considering the exploitation of natural gas hydrates and the impact of changes in earth temperature and pressure on the hydrate layer,mastering its thermal properties can not only further understand its thermal conduction mechanism and Physical and chemical properties,but also plays an important role in the exploration,development,storage and transportation of hydrates.Natural gas hydrates are generally formed in deep seabed or Qinghai-Tibet Plateau and other permafrost regions.It is extremely difficult to measure the thermal conductivity of naturally occurring hydrates in situ.This study simulates the formation conditions of natural gas hydrates,and uses a Hot Disk thermal constant analyzer and a hydrate thermal conductivity test bench set up by the laboratory to conduct research on atmospheric hydrate(THF hydrate)and high pressure hydrate(methane hydrate)on ex-situ measurement,it has formed a complete set of ex-situ test methods and procedures for hydrate thermal conductivity.And compared with the in-situ measurement results under the same experimental conditions and the measurement results in the literature,the errors of the ex-situ measurement and the in-situ measurement are obtained.The influence of the errors generated in each step on the measurement results,thereby further improving the measurement accuracy and accuracy.Through a large number of ex-situ measurement experiments of THF hydrate and methane hydrate thermal conductivity,the main conclusions are as follows:(1)Under the same experimental conditions,the ex-situ measured THF hydrate thermal conductivity as a function of temperature are consistent with the in-situ measurement results.The ex-situ measurement of the thermal conductivity is slightly larger than the in-situ measurement.The absolute error is 0.045 W/(m·K)?0.065 W/(m·K),and the relative error is 8.65%?12.01%.(2)The ex-situ measurement of the thermal conductivity of methane hydrate is slightly larger than the in-situ measurement.The absolute error is 0.0061 W/(m·K)?0.062 W/(m·K).The relative error is 1.24%?12.66%,and its dependence on temperature is not obvious.(3)The frost layer on the surface of the sample during the transfer of THF hydrate will increase the measurement result of the thermal conductivity by 0.30%?0.38%;the surface ice generated by methane hydrate under normal pressure due to its self-protection effect will increase the measurement result of thermal conductivity by 0.75%?0.77%.(4)During the ex-situ measurement of THF hydrate and methane hydrate,the errors of frost layer and roughness caused by the natural convection heat transfer between the sample and the probe are 8.35%?11.7%and 0.48%?11.9%respectively.(5)During multiple measurements,the uncertainty of the surface roughness of the methane hydrate sample has a greater impact on the thermal conductivity measurement results than the uncertainty of the THF surface frost layer on the thermal conductivity measurement results.