Theory of deepwater hydrocarbon accumulation controlled by progressive tectonic cycles of marginal sea in the South China Sea

At present, non-Atlantic continental margins such as marginal sea are a frontier of global deepwater oil-gas exploration. The South China Sea is one of the most famous marginal seas in the world, and its deepwater oil and gas accumulation mechanism is a scientific problem in frontier research. Based on the data analysis of geological transects and findings from ocean drilling, it has been proposed that the formation of the South China Sea is characterized with progressive tectonic cycles of marginal sea, 1. e., the SN-trending opening of the New South China Sea Basm was extending from east to west in the Late Oligocene to Miocene, and the SN-trending closure of the Ancient South China Sea Basin was extending from west to east in the Oligocene to Quaternary. The progressive tectonic cycles of marginal sea in the South China Sea controls the orderly development of basins and hydrocarbon accumulation factors. In the northern part of the New South China Sea, the formation of passive continental margin basins is characterized by "early in the east and late in the west". Specifically, the development of the Pearl River Mouth Basm in the east section began from the Eocene, which developed the Eocene and Lower Oligocene source rocks, the Eocene to Lower Miocene reservoir, and the Miocene to Quaternary thick mudstone cap rocks, showing a distribution of hydrocarbon-bearing strata from buried hill to Miocene. The development of Qiongdongnan Basin in the west section started from the Oligocene, which developed the Lower Oligocene source rocks, the Oligocene to Pliocene reservoir, and the Upper Miocene to Quaternary thick mudstone cap rocks, showing a distribution of hydrocarbon-bearing strata from buried hill to Pliocene. In the Ancient South China Sea, the formation of active continental margin basins is characterized by "early in the west and late in the east". To be specific, Zengmu Basin in the west section was formed in the Oligocene, which developed the Oligocene and Miocene source rocks, the Oligocene to Middle Miocene reservoir, and the Pliocene to Quaternary cap rocks, showing a distribution of hydrocarbon-bearing strata from Oligocene to Pliocene. The development of Brunei-Sabah Basin in the eastern section was initiated from the Middle Miocene, which developed the Miocene source rocks, the Lower to Middle Miocene reservoir, and the Quaternary mudstone cap rocks, showing a distribution of hydrocarbon-bearing strata from buried hill to Lower-Middle Miocene. Based on the above understandings, the paper proposes a new direction for oil-gas exploration in the marginal sea of the South China Sea. The new exploration strata of the deepwater area in the northern continental margin of the South China Sea are from the Paleogene to the buried hill reservoirs, and those in the southern active continental margin of the South China Sea are from Oligocene to Lower Miocene reservoirs. © 2023 Science Press. All rights reserved.