The Acoustic Characterization Numerical Simulation Of Nature Gas Hydrate And The Geophysical Comprehensive Research Of Gas Hydrate Reservoir In The South China Sea

Nature Gas Hydrate(NGH)plays a significant role as a clean energy.It is important to research the geophysical characterizations(such as sonic velocity,resistivity,etc.)of NGH.The research of the influence of different NGH patterns for geophysical characterization by using numerical simulation method can provide evidence for the selection of exploration methods.Following this,the NGH patterns can be distinguished by the differences of geophysical characterization,which is helpful to explain the formation of NGH under the sea floor.At the same time,Geophysical research can verify the abnormal geophysical characterizations and the feasibility of exploration methods,while comprehensive evaluation of various geophysical methods is more conducive to NGH distribution research and reservoir formation analysis.This paper includes three research sections with innovative achievements:(1)In this paper,we focused on the characterizations of the difference between pore-filling and cementation NGH patterns,and then compared the advantages and disadvantages of various numerical simulation methods.Based on the discrete element method(DEM)theory,the two pattern models are built by using the constraints of position,contact model and force among particles.Their porosity and saturation of the models are calculated.(2)The established numerical models are used to study the law of acoustic characterization of different hydrate patterns.Based on the process of laboratory wave velocity measurement,an innovative set of wave transmitting-receiving measurement in numerical simulation is proposed.According to measurement for sonic velocity of pore-filling and cementation NGH models at different saturation,we made the following conclusions: The P-wave velocity is between 1580m/s and 1810 m/s with the hydrate saturation in 0-40%.The higher the saturation grows,the greater the sonic velocity is.However,the velocity growth rate of cementation hydrate is much greater than that of pore-filling hydrate below 10% point.Otherwise,both hydrate patterns have the similar velocity growth rate in 10%-40% saturation range.(3)According to the Marine Controlled-source Electromagnetic method(MCSEM)research in the northern South China Sea,this paper provided the data processing and interpretation results.The MVO(Magnitude Versus Offset)and PVO(Phase Versus Offset)curves have been drawn and the abnormal resistivity layer under the survey line has been obtained by inversion.Based on comprehensive geophysical research,the results verified the abnormal geological characterization of NGH resistivity and feasibility of MCSEM exploration.Then,combined with seismic and logging data in the same region,which have been completed,we evaluated the gas distribution structure and positioned the abnormal layers.According to geological characteristics,the NGH formation process,the free gas migration paths and accumulation areas are interpreted preliminarily.