Hydrocarbons in shallow sediments of the western Ulleung Basin

서부 울릉분지 천부 퇴적층의 탄화수소

Studies on the hydrocarbons in shallow sediments of the East Sea of Korea have been carried out by the Korea Institute of Geoscience and Mineral Resources (KIGAM) since 2000. 4946 L-km of 2D multichannel reflection seismic data, 3250 L-km of high-resolution Chirp profiles and 16 selected piston cores were analyzed to determine the presence of hydrocarbons in shallow sediments of the western deep-water Ulleung Basin. The seismic data show a number of blanking zones that probably reflect widespread fluid and gas venting. The blanking zones are often associated with velocity pull-up structures. These upwelling structures are interpreted to be the result of high-velocity natural gas hydrate. There are also several bottom-simulating reflectors that are associated with free gas and probably overlying gas hydrate. Numerous pockmarks were also observed in the Chirp profiles. They are seafloor depressions caused by the removal of near-seafloor soft sediments by escaping of fluid and gas. In piston cores, cracks generally oriented parallel to bedding suggest significant gas content some of which may have been contained in gas hydrate in situ.