Experimental Study And Prediction Model Of Thermal Conductivity Of Hydrate-Bearing Sediment

Natural gas hydrates,found beneath permafrost and in marine continental margin sediments have gained worldwide attention because of its role of carbon cycle in the global and its character of high purity,high-energy density.At present,the world's explored organic carbon reserves are close to twice over total amount of the world's proven fossil fuels(coal,oil,natural gas).Distribution characteristics of Gas hydrate reservoir in the the south China sea sediments can be cementation,the phase change of the hydrate production process can be very violent,gas water transport and the change of composition,the characteristics of thermal conductivity of hydrate reservoir control and formation of the hydrate have important effect on heat transfer control,at the same time,characteristics of thermal conductivity is an important physical parameters of mining simulation program.As a crucial thermodynamic parameter,the thermal conductivity is essential to the study of the thermal properties of multiphase materials and is broadly adopted to evaluate the heat transfer process.The thermal conductivity of gas hydrate-bearing sediment must be given in order to do numerical or experiment research of decomposition and evaluate the economics of gas production.In this paper,the influence of the porosity and hydrate saturation on hydrate in the south China sea sediment samples of thermal conductivity properties has been studied,the influence of the thermal conductivity by heating and cooling samples gradient formation and decomposition of hydrate in samples has been studied,result shows that high saturation of the sample with a slight drop in hydrate decomposition coefficient of thermal conductivity,is likely to affect the heat and mass transfer process of hydrate production process;Due to the formation and decomposition of hydrate,the thermal conductivity of 100% hydrate saturated samples will change obviously.On the other hand,the artificial synthesis montmorillonite soil which is similar to the particle size distribution of Marine sediment has been made,experiments under different working conditions on thermal conductivity change caused by the internal phase has been made,the ice melts ice particles within the pore thermal bridge is destroyed,thermal conductivity droped 11%-30%,hydrate formation leads to the formation of a system of internal particles between the stability of the thermal bridge,thermal conductivity increases about 12% to 40% generally,thermal conductivity droped about 5%-29% which was caused by gas hydrate decomposition water moving and skeleton reconstruction,the rate are positively correlated with initial water saturation.The results show that the change of hydrate phase can cause the change of reservoir thermal conductivity,so the heat transfer should be strengthened in the recovery process.This paper compared the experimental results with the effective medium model,most existing model error is larger than expected,and make difficult to apply for South China sea sediment system,based on the formula of Pythagoras,a new fitting model which has the hydrate saturation variable parameter is established,the data of thermal conductivity in mining projects compared with result calculated by the prediction model,the average error is less than 13%;In addition,a thermal conductivity model suitable for spherical glass sand containing hydrate was proposed.The thermal resistance principle was introduced into the model.It was assumed that there was a thermal bridge of hydrate in the contact area of spherical particles,and a water layer was attached around spherical particles,the prediction error is acceptable.