Research On Reservoir Deformation In Natural Gas Hydrate Mining

The deformation effect of hydrate reservoir during mining is very important for safe and smooth exploitation.The East China Sea is one of the most important marginal seas in China,existing exploration data show that the Okinawa Trough West slope(Slope of the East China Sea)and the bottom region has gas hydrate.In this paper,we selected the natural gas hydrate prospect area in the Okinawa Trough as the research object.Based on the existing data we have,used the model of Mohr-Coulomb geotechnical constitutive relation and Biot consolidation theory,the deformation process of hydrate reservoir caused by intermediate step-down mining method based on ABAQUS finite element software is used to analyze the deformation process.The results show:1.The simulation results show that the hydrate is more easily decomposed in the deep reservoir,and the hydrate is decomposed from bottom to top in the reservoir.The decomposition distance of the reservoir is more than 2 times the decomposition distance at the top of the reservoir,and the reservoir deformation range is about 2 times that of the hydrate decomposition range.2.In the early stage of mining,the effective stress of the hydrate reservoir increases sharply,which makes the reservoir deformation in the early stage of mining,and the deformation amount is about 79% of the total deformation in 30 days.3.According to the results of the model calculation,the depressurization rate and range of deformation should be monitored slowly in the early stage of mining according to the different types of hydrate reservoir.Through appropriate differential pressure control reservoir deformation rate in the safe range,to achieve the purpose of evading disasters.