Structural controls on hydrocarbon migration traced from direct hydrocarbon indicators at the southwestern margin of the Ulleung Basin, East Sea

Abstract

This study presents a model for structural controls on hydrocarbon migration under the neotectonic regime at the southwestern margin of the Ulleung Basin in the East Sea, a marginal basin in the western Pacific. Based on comprehensive 3D multichannel seismic reflection and well data, we map the fault system and direct hydrocarbon indicators, including seismic chimneys and bright spots, at depths shallower than 1000 ms TWT (1144 m). We analyze the slip tendency of the 3D fault system based on current stress conditions newly estimated using focal mechanism data. Our results show that dextral strike-slip movements of NE–SW Group A faults, resulting in damage zones composed of subsidiary NW–SE to E–W Group B faults at tips and stepover zones, mainly accommodate the neotectonic deformation. The distribution of hydrocarbon indicators demonstrates spatial correlations with the fault system, indicating deformation-induced hydrocarbon migration and accumulation patterns. We emphasize that (1) along-fault zones and (2) releasing stepover zones of NE–SW Group A faults with a high tendency to slip have acted as main hydrocarbon migration pathways and accumulation zones. In addition, we suggest that trishear fault-related folding in a local transpression zone (the Gorae V anticline) can generate a forelimb with a high density of sub-seismic scale fracture corridors acting as active hydrocarbon pathways. Our findings increase the understanding of neotectonic deformation-induced hydrocarbon migration/accumulation patterns in the southwestern margin of the Ulleung Basin, contributing to assessment of hydrocarbon prospects, carbon dioxide capture and storage (CCS) opportunities, and submarine geohazards in western Pacific marginal basins with a similar tectonic setting.