Physical property interpretation of gas hydrate-bearing sediments using log data in the Ulleung Basin, East Sea

In order to investigate the presence of gas hydrate in the Ulleung Basin, the East Sea of Korea, Logging-While-Drilling (LWD) was conducted. The logged data acquired from LWD are electrical resistivity, acoustic velocity, neutron density and porosity, and natural gamma. In addition, density porosity was calculated using densities (log density and grain density). Clay volume and water saturation were also calculated based on log data using IP software. LWD data showed the evidences (e.g., velocity, resistivity, and density anomalies) indicating the presence of gas hydrate. The relationships among the physical properties showed the anomalous patterns relative to normal marine sediment, due to gas hydrate presence within sediments. In some depth intervals, clay volume calculated from log data deviates from core data. This is probably responsible for abundant volcanic ash and illite affecting natural gamma in the Ulleung Basin. Also the large amount of silt contents in the study area are likely affect to clay volume calculation. Based on water saturation, gas hydrate saturation is high above the gas hydrate stability zone. Occurrence type of gas hydrate is probably fractured-dominated within chimney structures.