Research On Methods Of Gas Hydrate Identification Based On Two-Phase Media Theory

Gas hydrate is a widely distributed, clean and efficient new energy which has great potential value. South China Sea continental margin of the seabed and the plateau permafrost gas hydrates are found to exist. Gas hydrates only is formed in the high pressure, low temperature stratum, climate change is very easy to break hydrate equilibrium temperature and pressure conditions, and cause significant harm. Therefore, knowledge of the basic nature of the hydrate such as porosity, saturation, permeability, is an important guarantee for the successful development of gas hydrate. Gas hydrate exists in a solid form of high porous unconsolidated rock matrix with various contact formation. In general, this medium is two-phase medium containing fluid, using the traditional single-phase theoretical analysis of seismic wave propagation characteristics hydrate is flawed.Based on the effective medium theory, this article analyze hydrates the elastic modulus of the rock matrix under different contact pattern, and the vertical gas hydrate formation, shear wave velocity and Poisson’s ratio with the formation porosity, saturation, and gas hydrate the variation of saturation; calculate the elastic modulus of gas hydrate formation in biphasic medium wave equation is based on the analysis under the influence of different factors porosity, hydrate saturation, gas saturation and permeability, speed P-wave, S-wave velocity and inverse quality factor versus frequency trends, to extract the relevant frequency and attenuation properties of the actual data from the theoretical basis.Two-phasic medium wave field is very complex, especially in multi-media, has many converted waves. In the solid phase, the energy of the fast compressional and shear wave is strong; in fluid phase, slow compressional wave energy is strong. From the Biot isotropic elastic wave equation, the polarization nature of the shear wave and compressional waves is different. So, seek divergence and curl, the wave field can achieve the separation. Established in line with the actual situation of hydrate formation, through the vertical separation of the transverse wave field snapshots and snapshots can be clearly identified formation interface, and can identify the BSR.AVO characteristics is an effective method for predicting reservoir lithology parameters require only a single-phase medium shear wave velocity and density can be expressed Zoeppritz equation, two-phase media need parameters, such as A, N, Q, R, ρ12, ρ11, ρ22, m1, m2. This paper presents the theory with walton instead Hertz-Mindlin theory, obtain the equivalent elastic modulus of rock when gas hydrates as a part of rock matrix, derive the Zoeppritz equations under different interfaces. Reflection coefficient variation with angle are discussed in detail under different model characteristics, and be compared with the single-phase medium AVO.According two-phase medium, velocity dispersion and attenuation characteristics is apparent, so the article apply two-dimension wavelet packet transform on the actual seismic data to isolate seismic records at different scales, extract properties such as dessert, attenuation, and other three instantaneous with different frequencies, and analysis BSR characteristics vary with frequency.