Modeling The Dissociation Of Methane Hydrate By Depressurization In Different-scale Cores

Methane hydrate is one of the most promis ing future energy resources for humankind.In recent years,due to its vast existence in permafrost regions and deep ocean beds,increasing attention has been paid to the extraction,transportation and utilization of methane hydrate.At present,with the joint efforts of scholars and researchers in the world,hydrate experiments,simulation,exploitation,theory and other aspects have made great progress.Knowledge system about hydrate is constantly being improved.Through the hard work of scholars and researchers in various countries,the theory of decomposition and formation of gas hydrate has been greatly developed,and the appropriate model has been put forward and verified experimentally.However,there are less attention paid to simulate the large-scale cores using the existing mature models.Based on the existing model,a two-dimens ional axisymmetric mathematical model of hydrate dissociation by depressurization in natural gas hydrate core is established,which includes three phases of water,gas and hydrate.The UDF program is written to solve and analyze the mathematical model in Fluent.By changing the parameters such as boundary conditions,thermodynamic conditions and specific surface area,time variations of different pressure,temperature,saturation,gas production rate,water production rate and heat absorption distribution are obtained to investigate the hydrate dissociation theory of large scale.The results show that: the rate of hydrate dissociation is a sensitive function the thermal conditions,ambient conditions,as well as of the outlet pressure;core porosity in porous media also affect the decomposition of gas hydrate;the temperature of hydrate close to the leading edge will first break down as hydrate dissociation,and then increase to ambient temperature with natural convection between core and the ambient temperature;the increase of ambient temperature will accelerate the rate of hydrate dissociation,while the gas production rate and water production rate will also be accelerated;the decrease of pressure will accelerate the rate of hydrate dissociation,and the rate of gas generation will also be improved;the UDF program help to simulate the hydrate dissociation in porous media,and construct a solid foundation for future research;hydrate began to dissociate at the outlet with time away from the outlet,and the gas saturation and water saturation are gradually increased;the results got from the small-scale and large-scale zones are nearly same.