Application Of Pre-stack Elastic Impedance Inversion In The Identification Of Gas Hydrate

As a highly promising new clean energy, natural gas hydrates has attracted wideattention of countries around the world due to its wide distribution, large reserves andclean burning. Theoretical studies show that the presence of gas hydrate can only bestable in the environment of low temperature and high-pressure. Once the temperatureand pressure conditions change, its stability will be destroyed. If hydrates exist underthe sea, it is likely to induce submarine slump followed by a series of natural disasters.It’s important to study its geophysical characteristics for both the pursuit of economicvalue of gas hydrates as energy sources and the will to prevent the disaster fromhappening.The purpose of this paper is to combine the elastic wave impedance technologywith gas hydrate exploration, and study characteristics of the geophysical parametersof gas hydrates. In terms of the identification of lithology and fluid, elastic waveimpedance inversion technique has become more and more reliable after beingapplied for years in the field of oil and gas exploration. The application of elasticwave impedance inversion technique in the field of gas hydrate has significantmeaning for the further research of hydrates.Firstly, using an appropriate rock physics model to study the relationshipbetween various lithologic parameters of the hydrate reservoir, analyze the changingtrend of the P-wave velocity, shear wave velocity and density under conditions ofdifferent porosity, different water saturation, different gas saturation and different gashydrate saturation. Then select the appropriate P-wave velocity, shear wave velocityand density information to forming a two-layer model of different hydrate reservoirand the overlying layer or the underlying layer for the theoretical researching.Analyzing the reflective properties of the hydrate reservoir at the top and the bottominterface, also analyzing the geophysical differences between the hydrate reservoir and the other layers around under this reflecting circumstance. According to thisdifference, select representative parameters to forming models contain several layersincluding hydrate reservoir.In majority of gas hydrate area, BSR can be obviously seen on the seismic profile.According to the formation mechanism of the BSR, with the condition of differentsurrounding layers, forming models of different classes of BSR to do research ofelastic impedance, analyzing its characterization of geophysics, especially thecharacters of P-wave impedance, shear wave impedance, density and lame constant.After a theoretical analysis, combining log data with seismic data of Marine gashydrate reservoir to do the pre-stack elastic wave impedance inversion of twodifferent areas, respectively. It turns out that using pre-stack elastic impedanceinversion technology can get good results in terms of identification of gas hydrate.