Seismic Data Processing And Hydrate Identification Of ODP Leg 204 On Hydrate Ridge

Gas hydrate is by hydrocarbon gas(mainly methane)and water under high pressure in low temperature environment formation of ice crystals compounds,mainly in the form of solid state occurrence in permafrost for land or sea sediments because of its huge reserves,clean pollution-free and the characteristics of the widely distributed,in today's growing energy shortage situation is known as the 21 st century most has the exploitation value of new energy source,attracted much attention.Bottom simulating reflector(BSR)has always been the important basis for hydrate identification,but in many cases BSR and hydrate are not one-to-one correspondence;then the feature that p-wave velocity and s-wave velocity in hydrate-contained sediment are increasing is used to identify gas hydrate.However,some non-hydrate factors could lead to the increasing of the p-wave and s-wave velocity.In order to improve the reliability of gas hydrate identification,the ratio of P-wave velocity increment to S-wave velocity increment which is proved by Professor Liu Xuewei can distinguish the high velocity characteristics caused by hydrate factor from non-hydrate.The research area of this paper is the ridge on the Cascadia accretion wedge on the edge of Central Oregon.In the past 20 years,a large number of geological,geochemical and geophysical data have been obtained in this area,and gas hydrate core samples have been obtained by drilling in the south of Hydrate Ridge.In this paper,the seismic response and physical characteristics of hydrate are analyzed by using the geological and seismic logging data of the study area,and the purpose of hydrate identification in the study area is finally realized.The research contents of this paper are mainly included three parts: Firstly,according to the characteristics of seismic data of ODP leg 204 and the geological task of hydrate identification,to obtain high signal-to-noise ratio sectionand angle stacking section for AVO inversion,we design a reasonable processing flow upon a seismic data processing software GeoEast.Through the analysis of the section,the possible seismic response characteristics of hydrate are identified,such as BSR,gas chimney,fault and so on.Then,pre-stack constrained sparse spike inversion is carried out by using inversion software Jason to obtain P-wave and S-wave velocity information of the study area.Finally,we use ?V_p/?V_s to obtain the ?V_p/?V_s section which could be used to complete the identification of hydrate.Through analysis,it is found that the position of hydrate in ?V_p/?V_s section profile corresponds to the position of high resistivity and high P-wave velocity of logging data,and the intersection diagram of bulk modulus and shear modulus in hydrate-free area is smaller than that in hydrate area,which accords with the results of theoretical research and confirms that the identified hydrate occurrence location is basically reliable.