Distribution and origin of seismic chimneys associated with gas hydrate using 2D multi-channel seismic reflection and well log data in the Ulleung Basin, East Sea

Abstract

Analysis of multi-channel seismic reflection and well-log data from the Ulleung Basin, East Sea reveals that two distinct types of seismic chimneys have been identified in the basin, based on their geometries, seismic reflection patterns, well log response, and lithology. Type-I is a mound-like feature with a transparent or chaotic reflection pattern. Well log interpretation and lithology of this type indicate that Type-I consists of mobilized homogeneous mud including fracture-filling gas hydrate. This type is mainly located on the structural highs, and is mostly restricted to the Pliocene sedimentary succession. In contrast, Type-II is a pipe-like feature with vertically stacked distorted-reflectors. Based on well log data and lithology, Type-II filled with fracture-filling gas hydrate without breaking up primary sedimentary structure. This type appears along the deep-seated fault, and mainly developed within the Quaternary deposit. Our primary conclusion is that Type-I resulted from the subsurface sedimentary remobilization in response to regional uplift in the Pliocene whereas Type-II resulted from the focused vertical fluid flow through fractures triggered by reactivation of deep-seated fault during the Quaternary.