SEISMIC ANISOTROPIC MODELING OF FRACTURE-FILLING GAS HYDRATE

Gas hydrate, existed as solid nodules or near-vertical veins filled in high angle fractures, is widely developed in the argillaceous deposits in deep basins. Such a fracture-filling gas hydrate may produce an anisotropic anomaly of high apparent resistivity. However, seismic wave propagation in the anisotropic hydrate layer is unclear. In this paper, a geophysical model of hydrate layer as such is established on the basis of logging data including velocity, density and dip of NGHP01-10 in the Krishna-Godavari (KG) basin of India. Then seismic response and propagation of gas hydrate-filled in fractures are modeled both in isotropic and anisotropic elastic wave conditions using the staggered-grid finite-difference method. Seismic modeling results show that isotropic velocity and amplitude are significantly different from anisotropic velocity and amplitude for gas hydrate-filled in fractures. Not only there are more reflections in anisotropic hydrate than those in isotropic hydrate, but also the average velocities of anisotropy are faster than those of isotropy.