--> --> Petroleum System Criticals of Cenozoic Rift Basin in the Northern East China Sea from Seismic Stratigraphy and Borehole Basin Modeling

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Petroleum System Criticals of Cenozoic Rift Basin in the Northern East China Sea from Seismic Stratigraphy and Borehole Basin Modeling

Abstract

The East China Sea Shelf Basin (ECSSB), one of most prospect area for oil and gas exploration in the world is the largest Cenozoic sedimentary ranging from the offshore of Jeju Island, South Korea to the north of Taiwan in the East China Sea. The northern ECSSB consists of three typical rift basins such as Domi, Socotra and Jeju basins filled by Cenozoic fluvio-lacustrine sediments with volcanic clastics and sills. Dragon Basin, a sub-basin of Jeju Basin in the northern ECSSB is developed along a series of NE-trending basement faults generally dipping toward SE. Through the analysis of 2D/3D seismic and the borehole basin modeling, we constrain the petroleum system criticals in this basin. The calculated burial history of the basin reveals the subsidence and uplift pulses. Uplift 1 from a regional crustal emergence which began in the Cretaceous and ended in the Paleocene, Eocene Tectonic Subsidence of Rift 1, Late Eocene to Early Oligocene Crustal Uplift 2, Early Miocene to Late Miocene Rift 2, and Late Miocene Crustal Uplift 3, and Pliocene Rift 3 Subsidence. According to seismic interpretation, three major uplifts are indicated by three major unconformities; the late Cretaceous unconformity at the top of the reflection-free to chaotic basement, the top of Eocene capping semi-continuous medium amplitude reflectors indicating the second major uplift, and the late Miocene unconformity caps semi-continuous bright reflectors, some exhibiting excellent offlapping wedges which maps the latest uplift. The top of Oligocene though demonstrating gentle sub-parallel truncation of the underlying semi-continuous reflectors does not show a distinct unconformity. The main potential source rocks in this basin are the Eocene lacustrine sediments which have good TOC (>1 wt%) with several hundred meters thick. Basin modeling suggests the Eocene sediment entered the oil window in the late Miocene (∼10 Ma), however, the upper formations of the basin are mostly immature. The maturity modeling of the basin is consistent with the result of Rock-Eval pyrolysis of core samples. A total of ∼45 mg/gTOC hydrocarbons were generated and charged to the Eocene formation, and no expulsion occurred due to over-burden rocks. Furthermore, several high amplitude anomalies are observed in 3D seismic data where the Eocene syn-rift sediments filled in half-grabens along NE-trending basement faults, suggesting that pre-Oligocene formation may have reservoirs charged with oil and/or gas potential.