Estimation of in-situ mechanical properties of gas hydrate-bearing sediments from well logging

Taking Well SH7 in South China Sea and Well Mount Elbert in Alaska North Slope permafrost as examples, mechanical properties of gas-hydrate-bearing sediments (GHBS) in ocean and permafrost were estimated based on the method used in conventional oil and gas reservoirs with log data, and the results were compared with other tests or calculations. The correlations between mechanical parameters and log velocities in conventional oil and gas industry can obtain reasonable strength parameters of oceanic GHBS, such as cohesion, internal frictional angle, tensile strength and shear strength. However, the estimations of shale content of oceanic GHBS, internal frictional angle of permafrost GHBS, elastic parameters such as Young's modulus and bulk modulus of oceanic and permafrost GHBS have big errors. In the future, more efforts should be given to build suitable relations between mechanical parameters and velocities or more accurate correlations between mechanical parameters and hydrate saturation. Thus, with the aid of velocities and hydrate saturations from well logging, the mechanical properties of GHBS can be more accurately evaluated.