Cenozoic fault system and its control on gas hydrate accumulation in the eastern Dongsha Island area, northern South China Sea: Insights from high-resolution 3D seismic data

Abstract

The enrichment and accumulation of natural gas hydrates depend on sufficient gas supply and effective migration pathways. The upward migration of deep thermogenic gases through fault systems is critical for seepage-type hydrate formation. This study aims to elucidate the developmental characteristics of Cenozoic fault systems in the eastern offshore area of Dongsha Island and their influence on natural gas hydrate formation. Utilizing high-resolution 3D seismic data, this study conducted a detailed structural interpretation and seismic attribute analysis to systematically investigate the spatial distribution, developmental stages, and dynamic mechanisms of the Cenozoic fault systems in this region. In addition, this study explored the role of these fault systems in facilitating the migration of deep thermogenic gases to the shallow strata. The study area is dominated by extensional and transtensional normal faults characterized by inherited development and relatively small fault displacements. The Cenozoic strata exhibit a tectonic framework of block-faulted uplift and subsidence with alternating highs and lows. Faults on either side of the central uplift dip in opposite directions and commonly exhibit parallel, step-like patterns. Differences in fault system attitudes were observed between the southern and northern parts of the study area. In the south, fault strikes remained consistent from deep to shallow levels, predominantly trending NE and NEE. In the north, fault strikes varied significantly with depth, transitioning from predominantly NEE in deeper strata to EW and NWW in shallower strata. The study identifies two distinct phases of Cenozoic fault activity: (1) 66-10 Ma, a regional extensional tectonic regime controlled fault development, resulting in the formation of NEE-trending normal faults; (2) 10-2.6 Ma, the Dongsha Movement influenced fault activity, during which EW- and NW-W-trending transtensional faults with dextral strike-slip characteristics developed in the Miocene strata of the northern region. The Cenozoic fault system played a significant positive role in facilitating the migration of deep thermogenic gas to shallow levels, thereby enabling the formation of natural gas hydrates.

Keywords

Gas hydrate / Combustible ice / Clean energy / Cenozoic / Structural features / Fault system / Geodynamic mechanism / Gas migration / Hydrate accumulation / High-resolution 3D seismic data / Geological survey engineering / Eastern Dongsha Island

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