Seismic interpretation and hydrocarbon accumulations implication of the Miocene Meishan Formation reefs in southern Qiongdongnan Basin, northern South China Sea

Deepwater oil and gas exploration has become a global hotspot in recent years and the study of the deep waters of marginal seas is an important frontier research area. The South China Sea (SCS) is a typical marginal sea that includes Paleo SCS and New SCS tectonic cycles. The latter includes continental marginal rifting, intercontinental oceanic expansion and oceanic shrinking, which controlled the evolution of basins, and the generation, migration and accumulation of hydrocarbons in the deepwater basins on the continental margin of the northern SCS. In the Paleogene, the basins rifted along the margin of the continent and were filled mainly with sediments in marine-continental transitional environments. In the Neogene-Quaternary, due to thermal subsidence, neritic-abyssal facies sediments from the passive continental margin of the SCS mainly filled the basins. The source rocks include mainly Oligocene coal-bearing deltaic and marine mudstones, which were heated by multiple events with high geothermal temperature and terrestrial heat flow, resulting in the generation of gas and oil. The faults, diapirs and sandstones controlled the migration of hydrocarbons that accumulated principally in a large canyon channel, a continental deepwater fan, and a shelf-margin delta.

Section: Petroleum Geology In Deepwater Settings In a Passive Continementioning

confidence: 99%

Petroleum Geology in Deepwater Settings in a Passive Continental Margin of a Marginal Sea: A Case Study from the South China Sea

Zhang

Feng

Yao

et al. 2021

“…The Qiongdongnan Basin is located at the northwestern part of the SCS, which is a Cenozoic quasi-passive continental margin petroliferous rift basin, structurally clamped between the Eurasian plate, the Pacific plate and the Indo-Australian plate (Taylor and Hayes, 1983;Dai et al, 2014;Wang et al, 2013;Qiu, et al, 2019). The deep-water area is about 9 × 10 4 km 2 in the south of the basin, containing a Central Depression zone and a Southern Uplift zone (Feng et al, 2017;Zhang et al, 2016) (Fig. 1).…”

Section: Geologymentioning

confidence: 99%

“…in recent years. These moundy reflectors have been understood differently: some were considered as reef (Wu et al, 2009;Ma et al, 2009;Chen et al, 2011;Feng et al, 2017); some as contourite deposits (Zhao et al, 2013); sediment waves ; channel deposits (Tian et al, 2016;Li., 2019); or results of water-rock reaction (He et al, 2012). So far, there is no clear answer to the scale, distribution, sedimentary characteristics, and sedimentary facies model of the contourite deposits in the southern Qiongdongnan Basin.…”

Section: Introductionmentioning

confidence: 99%

Seismic Recognition and Origin of Miocene Meishan Formation Contourite Deposits in the Southern Qiongdongnan Basin, Northern South China Sea

Feng

Ren

Lyu

et al. 2021

Research into the contourite deposits in the Upper Meishan Formation of the southern Qiongdongnan Basin in South China Sea is weak; their characteristics, distribution and original geological conditions are not clear. Using geological and geophysical methods including seismic and drilling data, based on seismic reflection characteristics, geometrical configuration description, and wave impedance inversion, two types of contourite deposits are recognized. Contourite deposits have blurred boundaries between each deposit and disordered internal seismic reflections; They are mound-shaped only in transverse section, and banded in the longitudinal direction. Type I contourite deposits are conical, with mediumhigh amplitude, low-continuity, low-frequency mound-shaped seismic facies, and subparallel-chaotic reflections internally. These deposits are conical with sharp tops, the canal between mounds is V-shaped and deep. The western wing is gentle and the eastern wing is steep, with the slope toe mostly between 10° and 20°, and width height ratio about 1-2. Type II contourite deposits are flat, exhibiting medium-amplitude, medium-continuity, low-frequency mound-shaped seismic facies, with subparallel weak reflections internally. Their mounds are flat with gently arced tops, with shallow canals between. The slope toe is between 5° and 10°, with a width height ratio of about 2-5. The wave impedance value of these contourite deposits is 4.6 kg/m 3 ×m/s to 6.8 kg/m 3 ×m/s, about 5.8 kg/m 3 ×m/s on average, which is presumed to represent marlycalcareous clastic sediments. The contourite deposits mainly develop beneath the slope break at the margin of the faultcontrolled platform in the Southern Uplift zone of the basin. In plane view, they are distributed approaching a west-to-east direction, and in section, lie in low-lying areas near the faults at fault-controlled terraces of the Southern Uplift zone, with a paleo-current direction nearly west-to-east. The paleotectonic setting of the gentle monoclinic platform was favorable for the development of such contourite deposits. The intensification of the Mid-Miocene deepest bottom current gave rise to the contourite-forming currents around the Southern Uplift zone in the northern South China Sea, which flow from Hainan Island to the Xisha Trough in a nearly west-to-east direction leading to the contourite deposits developing in the late Mid-Miocene transgressive environment, with multiple slow sea-level fall cycles.

“…Because of the important role of faults in hydrocarbon accumulation, the deformation and activity characteristics and activitymigration mechanisms of faults have been analyzed. Furthermore, the sealing capacity of faults was qualitatively evaluated, and then the formation models of composite migration transportation systems dominated by faults were also established (Nie et al, 2001;Yu et al, 2007;Hou et al, 2008;Shi et al, 2009;Zhang et al, 2010;Shao et al, 2013;Li et al, 2014;Sun et al, 2014;Xu et al, 2016;Zhang et al, 2016;Feng et al, 2017;Ye et al, 2017;Xie et al, 2017). The Yunkai low uplift is located in the southwestern part of the Baiyun sag in the Pearl River Mouth Basin.…”

Section: Introductionmentioning

confidence: 99%

Structural Characteristics and its Significances on Hydrocarbon Accumulation in the Yunkai Low Uplift, Pearl River Mouth Basin

Yang

Tianlong

Zhang³

et al. 2021

The Yunkai low uplift with low exploration degree is close to the Baiyun sag, and has hydrocarbon exploration potential in the deepwater area of the Pearl River Mouth Basin. Based on seismic and drilling data, balanced profiles and growth strata, this paper mainly discusses geological structures and formation processes of the Yunkai low uplift, and also analyzes the characteristics of fault system and their influence on hydrocarbon migration and accumulation. The EWtrending basement faults divide the Yunkai low uplift into two parts, i.e. the southern sector and the northern sector. The northern sector is a relatively wide and gentle uplift, while the southern sector is composed of two secondary half-grabens with faulting in the south and overlapping in the north. The Yunkai low uplift experienced three major formation stages, including the rapid uplifting stage during the deposition period of the Eocene Wenchang Formation, the slow uplifting stage during the deposition period of the Late Eocene-Middle Miocene Enping-Hanjiang formations, and the whole burial stage from the Middle Miocene to present. The extensional faults in the Yunkai low uplift and its adjacent areas strike mainly along the NW, NWW and near-EW directions. Also, the strikes of faults present a clockwise rotation from the deep to the shallow strata. According to effects of faults on hydrocarbon accumulation, the faults in the Yunkai low uplift and its adjacent areas can be divided into trap-controlled faults and source-controlled faults. The trap-controlled faults control trap development and can effectively seal oil and gas. The source-controlled faults connect directly source rocks and reservoirs, which are highly active during the rifting stage and weakly active since the Miocene. This activity features of the source-controlled faults is beneficial to migration of the early crude oil from the Baiyun sag to the high part of the Yunkai low uplift, but is not good for migration of the late natural gas. In the Yunkai low uplift and its adjacent areas, the traps in the deep Zhuhai and Enping formations that are close to source rocks in the Baiyun sag should be the favorable exploration objectives.