Determination of the Physical Properties of Sediments Depending on Hydrate Saturation Using a “Quick Look” Method

Abstract:

Seismic and electromagnetic measurements are promising tools for the detection and quantification of gas hydrate occurrences in nature. The seismic wave velocity depends among others on the hydrate quantity and the quality (e.g. pore filling or cementing hydrate). For a proper interpretation of seismic data the knowledge of the dependency of physical properties as a function of hydrate saturation in a certain scenario is crucial.

Within the SUGAR III project we determine such dependencies for various scenarios to support models for joint inversion of seismic and EM data e.g. for the shallow gas hydrate reservoirs in the Danube Delta. Since the formation of artificial lab samples containing pore filling hydrate from methane dissolved in water is a complex and time consuming procedure, we developed an easier alternative. Ice is very similar to hydrate in some of its physical properties. Therefore it might be used as analogous pore fill in a “quick look” experiment to determine the dependency of rock physical properties on hydrate content. We used the freezing point depression of a KCl solution to generate a dependency of ice saturation on temperature. The measured seismic wave velocity in dependence on ice saturation compares very well with data measured on a glass bead sediment sample with methane hydrate formed from methane dissolved in water. We could also observe that ice, formed from a salt solution in the pore space of sediment, behaves similar to methane hydrate as a non-cementing solid pore fill.