The AVO Technique Used In Hydrate Investgation

Gas hydrate is a cage-like solid formed by gas and water in the high-pressure and low temperature. It is widely distributed in continental margin continental slope and permafrost zone,which is a promising alternative energy sources. Hydrate exploration and research on the development of new energy, environmental protection and disaster prevention are extremely important, because China has long stretches of the coast and extensive permafrost.BSR is an important sign of recognition of gas hydrate, which corresponds to the dynamic marine gas hydrate stability zone bottom. It is the main method of pre-seismic exploration to understand the basic characteristics of BSR and to find BSR in the seismic profiles.AVO technology is a seismic exploration techniques to identify the characteristics of changes in lithology and reservoir using the change in amplitude versus offset, or amplitude versus angle analysis. The theory is based on Zoeppritz equations and its various simplified style.For the wave and shear wave properties of hydrate deposits, AVO forward modeling and inversion can be widely used in BSR identification, estimation of reservoir parameters and other aspects.In this paper, the first two hydrate model A and B of the three hydrate reservoir model proposed by Ecker is used. According to effective medium theory, Gassmann equation, Hashin-Shtrikman-Hertz-Mindlin theory, and the Willy average time equation he calculates hydrate reservoir longitudinal wave velocity, poisson ratio, density and other physical parameters. Also he discusses the P-wave velocity– porosity, saturation curves and poisson's ratio– saturation curve of hydrate and free gas layer.And on this basis, he forwards the reflection coefficient curve of different saturation of the hydrate layer overlying a variety of free gas saturation or water-saturated sediment layer,under a certain porosity, using Shuey formula.Later, he carrys on AVO forward modeling of level hydrate (A-type) layer by Tesseral software based on the physical parameters of the elastic modulus the model.Therefore, he gets the different AVO characteristics of BSR and estimates the influence of gas hydrate or free content on the BSR.After the forward modeling, he discusses the influence of the sub-wave frequency, type, thin-layer, porosity, pore shape, quality factor and weak TIV medium on the AVO reflection coefficient curves.Finally, by the process of AVO seismic data in a sea,he gets the AVO attribute section, and confirms the existence of hydrate layer in the area.