Identification And Saturation Estimation Of Marine Gas Hydrate

Gas hydrate is regarded as a kind of new energy,with the advantages of high energy,large reserves,wide distribution and shallow burial.It is of great significance to accurately identify hydrate from marine sediments and estimate the hydrate saturation.Based on rock physics model,we simulate seismic attributes of the hydrate and non-hydrate bearing sediments.According to the difference properties,we put forward methods of hydrate identification and hydrate saturation estimation,which are verified by the data from the South China Sea and Hydrate Ridge successfully.Theoretical simulations show that there are differences on velocity and density between hydrate and non-hydrate bearing sediments.Therefore,we propose the new attributeV_p.⁰⁵/?⁵,which displays opposite trends increasing with saturation for hydrate and non-hydrate bearing sediments.We can compare the measuredV_p.⁰⁵/?⁵ to theV_p.⁰⁵/?⁵ of seawater-saturated sediments to identify hydrate.The logging data from the South China Sea and Hydrate Ridge has proved this method is feasible.The P-and S-wave velocity of hydrate and non-hydrate bearing sediments is also different.We use the P-and S-wave velocity of cross plot analysis to identify the hydrate and non-hydrate bearing sediments.Moreover,the hydrate saturation range can be estimated by the cross plot of P-wave and S-wave velocity increment.The logging data of Hydrate Ridge verifies this method,and the estimated hydrate saturation is mainly in line with the saturations estimated by Cl^-concentration.The amplitude-versus-offset(AVO)patterns of reflection interfaces beneath different minerals bearing sediments are studied in this paper,which provides an approach to identify pore-filling hydrate deposits.The forward simulations obtain class?AVO patterns for pore-filling gas hydrate deposits and class ?AVO patterns for other pore-filling minerals deposits.We verify this method by the actual seismic data from the South China Sea,in agreement with theoretical results.We also propose different inversion methods to estimate hydrate saturation for pore-and fracture-filling hydrate sediments.And the fracture dip angles are also considered for fracture-filling hydrate sediments.In the actual application,the estimated results are generally consistent with the measured saturations based on Cl^- concentrations.