The First Commercial Production of the Ulleung Basin, Offshore Korea

Byenggoo Choi, Choi Suyoung, Hun Jeong, Hyeon-gyu Kim, Yongsu Lim, and Byeongwook Yoo
Korea National Oil Corporation, Anyang, South Korea

Continued hydrocarbon exploration of offshore Korea Block VI-1 since 1970, resulted in the first gas and condensate production of the Ulleung basin, offshore Korea in 2004. Among 20 wells which have been drilled in water depth from 100 to 250 meters, 12 wells were recorded as discoveries.

Hydrocarbon accumulations in the Ullueng basin occur in shelf and deep water Miocene sediments, such as prograding deltas and submarine fans. Two petroleum systems are recognized in the basin by exploration activities: 1) middle to late Miocene terrestrial source rocks generated gas and condensate, and charged middle to late Miocene shelf sandstone reservoir rocks in Pliocene to Pleistocene time, 2) syn-rift and early post-rift sediments provided gas accumulations which were trapped mainly in middle Miocene deep water sediments. The former petroleum system has been evaluated by the production field data and the latter has been established by conceptual modeling and gas discoveries.

A distinct structure shows northeast-southwest trending faults which are probably related with the back-arc opening and closing movements. All of the drilled prospects in the block are within the structure created by compression and deformed by shear stresses.

The production of the gas field triggered the exploration of Miocene sediments within and around the structure and provided another discovery in 2005.