Abstract
In recent years, several large gas fields have been discovered in western Qiongdongnan Basin. It is important and necessary to illustrate their sedimentary characteristics and hydrocarbon migration so that more gas fields could be discovered in the future. Previous regional tectonic-sedimentary researchers show that large-scale source rock of the Yacheng Formation developed in the Ledong and Lingshui sags due to the Red River Fault pull-apart strike slip in early Oligocene. The main targets for hydrocarbon exploration in this area are the Miocene deep water reservoirs. In late Miocene, the Huangliu Formation reservoirs are composed of the early channels which were sourced by river systems in Hainan uplift and the consequent channels were sourced by Qiupen River in Kunsong uplift. Both axial channels exhibit unique spatial distribution patterns and geometries. The other kind of reservoir developed in the middle Miocene Meishan Formation, which compose of slope break-controlled submarine fan. They can be further classified into three types—slope channelized fan, basin floor fan, and bottom current reworked fan. The various fans have different reservoir quality. These two kinds of reservoirs contribute to four types of litho-stratigraphic traps under the actions of sedimentation and subsidence. The overpressure caused by hydrocarbon generation can fracture deeper strata and result in regional fractured network for hydrocarbon migration. Therefore, free gas driven by overpressure and buoyancy force can be migrated into Miocene litho-stratigraphic traps to accumulate. The revealed genesis of Miocene lithologic trap and hydrocarbon accumulation in the Qiongdongnan Basin would greatly contribute to the further hydrocarbon exploration in northern South China Sea and can be helpful for other deep water areas around the world.
Highlights
Seismic stratigraphic correlation shows the super-thick early Oligocene (the Yacheng Formation) developed in the Ledong and Lingshui sags, while the Eocene is only restricted to subsidence centers, and its range of distribution gradually decreases from north to south
Qiongdongnan basin is a Cenozoic petroliferous extensional basin which is located in the continental margin of the northern South China Sea and southeast of the Hainan Island
The terrigenous clastic sediments carried by the Qiupen river flowed down from the Kon Tum Uplift were accumulated in the Ledong Sag, and moved eastward, so the abundant sediment supply from the west increased the topographic gradient of the eastern Qiongdongnan Basin, accelerating effect of gravity fluid flow which led to the formation of deep straight restrictive canyon
Summary
Seismic stratigraphic correlation shows the super-thick early Oligocene (the Yacheng Formation) developed in the Ledong and Lingshui sags, while the Eocene is only restricted to subsidence centers, and its range of distribution gradually decreases from north to south. The terrigenous clastic sediments carried by the Qiupen river flowed down from the Kon Tum Uplift were accumulated in the Ledong Sag, and moved eastward, so the abundant sediment supply from the west increased the topographic gradient of the eastern Qiongdongnan Basin, accelerating effect of gravity fluid flow which led to the formation of deep straight restrictive canyon.
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