A Quick Look Method to Assess the Dependencies of Rock Physical Sediment Properties on the Saturation With Pore-Filling Hydrate

Within the framework of the national German hydrate project Submarine Gas Hydrate Reservoirs (SUGAR) we promised to deliver dependencies of compressional-wave velocity and electrical resistivity on hydrate saturation within sand sediments of the paleo Danube channel-levee system in the Black Sea. These data supported starting models for joint inversion of seismic and electromagnetic geophysics data for that area. Because hydrate formation in sediment samples under laboratory conditions is a complex and particularly time-consuming procedure, we developed a quick look experimental methodology. We used ice as an analogue for methane hydrate to simplify the experimental procedure for laboratory studies. The difference from existing approaches is the way the ice and water saturation of the porous sediment is determined. To verify this approach, we compared the new data measured on ice-bearing sand with measurements on hydrate-bearing sediments, where methane hydrate was produced from methane dissolved in water. The main result from this study is that ice forming from a salt solution in the pore space of sand forms like methane hydrate as a noncementing solid pore fill. The method does not require a pore pressure system and produces a homogeneous ice distribution, as long as homogeneous temperature distribution throughout the sample can be guaranteed. For compressional-wave velocity measurements we demonstrate that ice can be used as an analogue for noncementing methane hydrate. Therefore, the complete dependence of velocity on ice saturation, depending on the saturation increment, can easily be measured in 1 to 2weeks.