Genesis of Miocene litho-stratigraphic trap and hydrocarbon accumulation in the Qiongdongnan Basin, northern South China Sea

Geoscience Letters, Apr 2018

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.

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Genesis of Miocene litho-stratigraphic trap and hydrocarbon accumulation in the Qiongdongnan Basin, northern South China Sea

Fan et al. Geosci. Lett. Genesis of Miocene litho-stratigraphic trap and hydrocarbon accumulation in the Qiongdongnan Basin, northern South China Sea Caiwei Fan 1 Tao Jiang 0 Kun Liu 1 Jiancai Tan 1 Hu Li 1 Anqi Li 1 0 Key Laboratory of Tectonics and Petroleum Resources of Ministry of Education, China University of Geosciences , Wuhan 430074 , China 1 Zhanjiang Branch of CNOOC Ltd. , Zhanjiang 524057, Guangdong , China 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. Qiongdongnan Basin; Ledong sag; Lingshui sag; Axial channel; Submarine fan; Litho-stratigraphic trap; Overpressure; Hydrocarbon accumulation Introduction 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. It stretches northeastward with alternating depressions and uplifts framework and can be subdivided into northern depression, middle uplift zone, middle depression, and south uplift zone, including 10 sub-depressions, such as Yannan sag, Yabei sag, Ledong sag, Lingshui sag, and so on (Fig.  1). The Ledong and Lingshui Sags are the two largest sags in the Qiongdongnan Basin, characterized by deep burial strata, thick deposition, high temperature, and overpressure (Xie et  al. 2006; Pettingill and Weimer 2002) . However, the hydrocarbon exploration potential in these two sags was not considered to be promising for a long time due to three reasons. Firstly, the resource potential was quite uncertain. Limited by poor seismic data in the past, the scale and distribution of Oligocene source rock (the Yacheng Formation) could not be clearly identified. Secondly, fault activity in most regions was absent or resting since Neocene. Possibility and efficiency of hydrocarbon vertical migration were dubious. Thirdly, owing to a lack of well and 3D seismic data, there were enormous controversies on provenance, formation mechanism, and reservoir spatial distribution of axial channels (Antbreh and Krastel 2006; Su et  al. 2013; Xu et  al. 2012; He et  al. 2011) . The shortage of basic geological information restricted the understanding of the petroleum system in western Qiongdongnan Basin. Moreover, exploration confidence in this field was severely defeated by all failures in well drilling in the past. In recent several years, large-scale high-quality 3D seismic acquisition and application, including the widespread application of pre-stack depth migration in slope break belt, make it possible to identify and evaluate Paleogene the Yacheng Formation as source rock, which is also favorable for Miocene seismic sedimentology, paleotopography, and sedimentation researches. With the help of high-resolution electric image logging technology, sedimentary textures associated with reservoir formation environment can be clearly identified. Moreover, this study conducted the pressure–accumulation relation research and description of fracture net which can be served as vertical migration paths. Research results illustrate reservoir-forming mechanism using new 3D data and advanced imaging logging technology, which is helpful for gas exploration and leads to the recent breakt (...truncated)


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Caiwei Fan, Tao Jiang, Kun Liu, Jiancai Tan, Hu Li, Anqi Li. Genesis of Miocene litho-stratigraphic trap and hydrocarbon accumulation in the Qiongdongnan Basin, northern South China Sea, Geoscience Letters, 2018, pp. 13, Volume 5, Issue 1, DOI: 10.1186/s40562-018-0112-0