The Deeper and the Deeper, New Plays in the Ulleung Basin, Offshore Korea

Chang Seok Jeong, Kook-Sun Shin, Kiho Bae, Donghyun Lim, Hyeongyu Kim, Suyoung Choi, Seongwan Park, Chulbaek Kim, and Kyoung A. Lee
Domestic Exploration, Korea National Oil Corporation, Anyang, South Korea

A series of gas discoveries since '80s resulted in the first gas production of the Ulleung Basin in 2004. Additional gas reserves have been discovered around the gas field from the present shelf environment, water depth around 200 meters and the depth of reservoirs about 3,000 meters from mean sea level. The gas production and additional discoveries proved the acting petroleum system of the Miocene clastic sediments in the basin.

Based on the petroleum system analysis, new two plays are identified in the basin. The first is the Miocene and Pliocene submarine fan systems in the present deep water. The northeast trending prograding features of the Miocene sediments are dominant seismic characteristics. Hydrocarbon explorations have been limited up to the water depth of around 300 meters in the basin up to now. New exploration potentials from the deep water area have been emphasized by 2-D and 3-D seismic data evaluation recently.

The deepest well in the basin is 4,600 meters which was designed for drilling of thrust structures and the old sediments which were deposited during basin opening and early post-rift stage have not been penetrated. There were two distinguished tectonic movements associated with structural forming; the first was compression stress caused by the collision between the Asian and the Pacific plates at around 10.5 Ma age and the second was shear stress caused by oblique subduction of the Pacific plates due to its change of plate movement direction at around 5.5 Ma age.

Most of the gas production and discoveries are from the structures associated with the recent wrench movements. The older structures which were created by the compression are not well tested in the basin due of their burial depth. The significant potential of the deeper water and the deeper formation plays will be revealed by the scheduled exploration activities in the near future.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas