A case study on the applicability of elastic velocity models to hydrate-bearing sediments

Abstract

Acoustic properties play an important role in the identification of natural gas hydrate resources, the estimation of their potential yield and the evaluation of soil stabilisation during exploration. Physical properties, such as hydrate saturation, porosity and clay content, are dominant factors that affect the acoustic properties of sediments. When considering these properties, the modified Biot–Gassmann theory of Lee (BGTL), the effective-medium theory (EMT) and the Frenkel–Gassmann equation (FG) are adopted to show the characteristics of compressional and shear wave velocities due to variation of the physical properties of different sediments. The results show that hydrate saturation has the highest sensitivity in the three models, followed by the porosity and clay content. To evaluate the applicability of different models, the data from two case studies are compared – actual survey data from the site995 stations and 2L-38 logging. The results indicate that the BGTL and EMT models are more suitable for hydrate-bearing sediments with a hydrate saturation less than 10%, a clay content of 50–70% and a porosity of 60–70%, while the FG model is more suitable for hydrate-bearing sediments with a hydrate saturation of 30–70%, a clay content of 30–60% and a porosity of 30–50%.