Mathematic Forward Modeling Research On Seismic Characteristic Of Marine Gas Hydrate

Marine gas hydrates represent a potential future energy resource and might have a strong greenhouse effect on global climate. In seismic data, it is often associated with bottom simulating reflectors (BSR) and blanking zone. Therefore the research on the cause of BSR and blanking zone is very necessary in gas hydrate research.In this thesis, the hydrate formation is classified into three micro models according to rock-physics research on hydrate. The three models are: (A) hydrate is part of the pore fluid, (B) hydrate becomes part of the solid frame, and (C) hydrate cements grain contacts together. Then by comparing five methods of estimating the elastic parameters of hydrate sediments, I select the suitable one for each micro model. Finally, using the forward 1-D modeling and amplitude versus offset (AVO) technology I examine the three micro models to infer the possible cause of BSR, blanking zone and analyze the validity of AVO in hydrate research.The research on BSR shows that there exists a critical saturation and for different micro model, its critical saturation is also different. When the hydrate saturation is less than the critical saturation: a) the AVO curve can indicate whether there exists any free gas below the BSR; b) if there is no free gas below, only when the micro model is model C can BSR be visible in seismogram. While the hydrate saturation is more than the critical saturation: a) the AVO cannot curve indicate whether there exists any free gas below the BSR; b) the BSR is always visible in seismogram whether there exists free gas below or not.The research on blanking zone shows that the variation hydrate saturation is altering with porosity in the blanking zone. The comparison between synthetic seismograms of different models indicates that the detail change of porosity and the mode of saturation changing with porosity are more complicated than assumed before.The thesis testifies that the cause of BSR and blanking zone can be explained with different models. It indicates that only integrated different methods such as geophysics and geology can overcome the nonuniqueness and improve the accuracy, credibility of inverse problem in marine hydrate research.