Equivalent Compressional Wave Velocities Of Gas Hydrate Bearing Rocks And Their Influencing Factors

Natural gas hydrate as a potential clean energy caused the wide attention from all over the world,countries around the world in terms of natural gas hydrate is inversion made many achievements,on the seismic identification of natural gas hydrate(NGH)also found many problems,including natural gas hydrate formation recognition based on BSR reflection interface went wrong,In the forward aspect,for application of rock physics model,predecessors have given a lot of ways,for the past such as Wood,rock physics model equation,Lee weight equation and Wyllie time average equation and its application in rock containing gas hydrate has achieved very good results,but these models are not considering the influence of rock pore shape.This paper based on the predecessors’ research results,considering the recognition of gas hydrate and its complex in the nature of the deposit,containing porous media,several classical equivalent model is employed to make the calculation of equivalent velocity analysis,studied the different mineral constituent,porosity,and hydrate saturation effect on the rock containing gas hydrate p-wave velocity,The advantages and disadvantages of different models and their applicable scope are analyzed.Then,the SCA self-consistent model is used to study the effects of different pore shapes on the physical parameters and compressional wave velocity of NGH bearing rocks.Finally,the relationship between the equivalent compressional wave velocity and the hydrate saturation of surrounding rock and the fracture parameters is calculated based on Hudson’s theoretical model.Research has shown that different pore shape for the elastic modulus of the rock containing gas hydrate and p-wave velocity has a big impact,in the needle and the contrast of spherical pore,the longitudinal wave speed can reach more than 200 m/s the biggest difference,in coin form pore,the bigger the aspect ratio of the pores of the rock,its corresponding the smaller the elastic modulus and longitudinal wave velocity.From Hudson model,the equivalent of compound rock filling type including hydrate p-wave velocity will increase with the increase of surrounding rock of hydrate saturation,whatever the fissure filling material in the overall trend is the same,compared with fracture density,in the case of low fracture density,its equivalent longitudinal wave velocity will decrease with the increase of fracture density.