Elastic-wave velocity in marine sediments with gas hydrates: Effective medium modeling

We offer a first-principle-based effective medium model for elastic-wave ve locity in unconsolidated, high porosity, ocean bottom sediments containing gas hydrate. The dry sediment frame elastic constants depend on porosity, e lastic moduli of the solid phase, and effective pressure. Elastic moduli of saturated sediment are calculated from those of the dry frame using Gassma nn's equation. To model the effect of gas hydrate on sediment elastic modul i we use two separate assumptions: (a) hydrate modifies the pore fluid elas tic properties without affecting the Framer (b) hydrate becomes a component of the solid phase, modifying the elasticity of the frame. The goal of the modeling is to predict the amount of hydrate in sediments from sonic or se ismic velocity data. We apply the model to sonic and VSP data From ODP Hole 995 and obtain hydrate concentration estimates from assumption (b) consist ent with estimates obtained from resistivity, chlorinity and evolved gas da ta.