Structure, stratigraphy and petroleum geology of the SE Nam Con Son Basin, offshore Vietnam

Abstract

New well and seismic data acquired during recent exploration of the SE Nam Con Son Basin, offshore Vietnam, have been evaluated to assess the tectonostratigraphic evolution. The offshore Vietnamese region has evolved in response to the complex relative motions of Indochina, Peninsular Malaysia, Borneo and the East Vietnam/South China Sea during the Cenozoic. On a regional scale these motions have been accommodated by strike-slip fault development, crustal extension and contraction. Rift pulses occurred in the SE Nam Con Son Basin from the Palaeogene to the earliest Late Miocene in response to the interaction of East Vietnam/South China Sea rift propagation and regional transtensional shear to the west of the evolving ocean basin. The structural evolution was complicated by mild contractional deformation during the Middle Miocene which was broadly synchronous with development of the largest inversion structures in the nearby West Natuna Basin. The oldest dated Tertiary rocks in the SE Nam Con Son Basin are fluvio-deltaic sediments of Late Oligocene age which have been penetrated by several wells. Early to Mid-Miocene depositional environments ranged from non-marine to outer shelf, with a predominantly clastic basin-fill. The thickest Lower to Middle Miocene occurs in N-S- to NE-SW-trending half grabens. A regionally recognized truncational unconformity of late Mid-Miocene age has resulted partly from the combined effects of the mild inversion and by the erosion of uplifted footwalls. During the Late Miocene there was rapid and widespread deepening of depositional environments, synchronous with net-extensional fault reactivation on many previously developed rift structures. The stratigraphic response to this increased bathymetry was the growth of isolated carbonate build-ups on pre-existing structural highs, progradation of the palaeo-Mekong delta system and associated deep-marine submarine channel development and erosion. This pulsed structural and stratigraphic evolution has resulted in deposition of source, reservoir and seals, and produced a variety of potential trapping styles.

Seismic reflection evidence for a Dangerous Grounds miniplate: No extrusion origin for the South China Sea

“…We follow the reconstruction of Lee and Lawver [1995] in placing the almost unextended Reed and Macclesfield banks adjacent to one another prior to breakup (Figure 12). Our reconstruction also accounts for extension in the Nam Con Son and Cuu Long basins [Matthews et al, 1997] and in the Nha Trang Basin [Roques et al, 1997a]. The former northeastern edge of Borneo is restored prior to addition of the Rajang/Crocker accretionary complexes, following the maps of Hall [2002].…”

“…The Mekong offshore region is characterized by two deep SW-NE oriented basins, the Cuu Long and the Nam Con Son (Figures 1 and 2), whose extensional history is closely linked to the southwestward propagation of the seafloor spreading center in the South China Sea during the early Miocene [Lee et al, 2001;Matthews et al, 1997]. South of where the now extinct propagating rift tip intersects the EVTZ, the continental margin is quite different in tectonic character compared to that seen north of that point.…”

Tectonic-stratigraphic division and blind fold structures in Nansha Waters, South China Sea

“…Based on drilling data from various basins circling the Nansha region, there have established several stratigraphic schemes by various researchers, e.g., Taylor and Hayes (1980) in Liyue (Reeds) Bank, Hinz and Schluter (1985), Schluter et al (1996), and Sales et al (1997) in offshore Palawan, Mohammad and Wong (1994) and Mat-Zin and Tucker (1999) in the deepwater area offshore Sarawak (Sarawak Basin), and Matthews et al (1997); Lee et al (2001) in the west Wan'an Basin (Nam Con Son Basin) offshore Southeast Vietnam. Within these basins, thick Cenozoic deposits developed pervasively.…”

Seismic Interpretation of the Nam Con Son Basin and its Implication for the Tectonic Evolution

“…This combination possibly derived N -S extension in the Sunda Shelf (Hall, 2002(Hall, , 2009(Hall, , 2013Hutchison, 2004;Clift, 2008). Matthews (1997) and Fyhn et al (2009) proposed the onset of rifting in the proto East Vietnam Sea (EVNS) as well as the NCSB initiated in the Eocene and lasted to the Early Oligocene (about 30 Ma). This rifting period is controlled by N-S extension, associated with E -W oriented faulting and deposition of rift-fill sediments in local W-E trending subbasins (Figure 2).…”