Characteristics and Hydrocarbon Generation of the Marine Source Rock of the Upper Oligocene Zhuhai Formation in the Baiyun Sag, Pearl River Mouth Basin, South China Sea

Abstract

The Baiyun Sag, located in the northern South China Sea, is rich in oil and gas. The marine mudstone in the Upper Oligocene Zhuhai Formation of the Upper Oligocene has not previously been considered as the main source rock and was thus selected for a thermocompression simulation experiment to verify its hydrocarbon generation potential. The experimental results were used to calculate the hydrocarbon generation kinetic parameters, and the hydrocarbon generation process of the marine mudstone was simulated. The mudstones of the Upper Oligocene Zhuhai Formation in the deepwater area of the Baiyun Sag are effective source rocks. The dark shallow marine mudstones of the Upper Oligocene Zhuhai Formation from well C generate hydrocarbons at a rate of 179.79 kg/ton of total organic carbon. As a set of active source rocks, the Upper Oligocene Zhuhai Formation has reached the low mature to mature stage and mainly generates oil in the marginal areas of the Baiyun Sag, whereas they have reached a highly overmature stage and generate both oil and gas in the central areas.

Impact of Paleosalinity, Dilution, Redox, and Paleoproductivity on Organic Matter Enrichment in a Saline Lacustrine Rift Basin: A Case Study of Paleogene Organic-Rich Shale in Dongpu Depression, Bohai Bay Basin, Eastern China

“…Dilution is defined as the organic-carbon-free sedimentation rate, which is mainly terrigenous detrital matter for lacustrine basins. , The major element contents of Fe and K can be used to trace the influence of the terrigenous detrital matter . The (Fe + K) contents in the Es 3 L shale are generally greater than that of the Es 3 U shale, indicating that the terrigenous detrital matter amounts are much greater in the Es 3 L shale, especially in the depth interval of 3340–3385 m with the highest content of 10.35% (3374.56 m) (Figures e and e), and the frequently interbedding of shale and siltstones in this depth interval further illustrates the great terrigenous detrital matter input in this depth interval (Figure b).…”

“…Dilution and Its Control on Organic Matter Enrichment. Dilution is defined as the organic-carbon-free sedimentation rate, 6 which is mainly terrigenous detrital matter for lacustrine basins. 25,28 The major element contents of Fe and K can be used to trace the influence of the terrigenous detrital matter.…”

“…The shale gas and oil revolution of North America changed the world energy structure and stimulated shale oil exploration and research in many other countries around the world. Precise prediction of “sweet spots” is one of the key musts for successful shale oil exploration. − Recent studies indicate that the organic matter content in a shale determines the hydrocarbon generation capacity of the shale, − affects the pore space development, ,− and strongly correlates to the residual hydrocarbon (adsorption) capacity. ,,,− Therefore, shale oil “sweet spots” and organic-rich intervals are closely related, − , and determination of the main factors controlling organic matter enrichment in shales is of great significance.…”

“…On the basis of the above models, some scholars studied the organic matter enrichment conditions in the shales in the Yangtze Platform, , northern South China Sea, and Jianghan Baisn with respect to paleoproductivity, redox conditions, and dilution. Massive shale oil resources were recently discovered in many SLRBs in China, such as the Paleogene shale oil plays in the Dongpu Depression, Bonan Sag, and Dongying Depression , in the Bohai Bay Basin; Biyang Depression in the Nanxiang Basin, Jianghan Basin; − , and the Permian shale oil plays in the Jimusar Sag in the Junggar Basin. , However, studies on the main factors controlling organic matter enrichment in shales of the SLRBs are still lacking. − Recently, some research started focusing on SLRB shales. Ding et al.…”

Mechanism of Organic Matter Accumulation in Residual Bay Environments: The Early Cretaceous Qiangtang Basin, Tibet

“…Developing an understanding of the properties and genesis of hydrocarbon source rock is of the utmost importance in oil-gas exploration. − Generally, depositional environments of source rock can be divided into two end-member settings, i.e., shallow-to-open marine and continental lacustrine, − while during the change from marine to continental deposition, a residual bay basin can develop, whereas, during the transition from continental to marine deposition, a transgressive lacustrine basin (a coastal lacustrine basin) can form. − Such kinds of modern examples/analogues include the Bohai Bay Basin in eastern China and the bay of Brest in France, which were both influenced by the Holocene marine transgression. , They have become research highlights for decades and set the controlling mechanisms related to the accumulation, and preservation of organic matter in these transitional settings are not well understood due to the complex compositions of bioprecursors, although oil–gas source rocks can form in this setting. ,,, …”