The Bạch Hổ oil field (White Tiger oilfield) is a major

oil field A petroleum reservoir or oil and gas reservoir is a subsurface accumulation of hydrocarbons contained in porous or fractured rock formations. Such reservoirs form when kerogen (ancient plant matter) is created in surrounding rock by the presence ...

in the Cuu Long basin of the East Sea located offshore due east of the

Mekong Delta The Mekong Delta ( vi, Đồng bằng Sông Cửu Long, lit=Nine Dragon River Delta or simply vi, Đồng Bằng Sông Mê Kông, lit=Mekong River Delta, label=none), also known as the Western Region ( vi, Miền Tây, links=no) or South-weste ...

Vietnam Vietnam or Viet Nam ( vi, Việt Nam, ), officially the Socialist Republic of Vietnam,., group="n" is a country in Southeast Asia, at the eastern edge of mainland Southeast Asia, with an area of and population of 96 million, making i ...

. The field contains major reserves hosted within highly fractured granitic basement rocks. The Cuu Long basin is a

rift In geology, a rift is a linear zone where the lithosphere is being pulled apart and is an example of extensional tectonics. Typical rift features are a central linear downfaulted depression, called a graben, or more commonly a half-grabe ...

zone developed during the

Oligocene The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but the ...

to Early

Miocene The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recen ...

. The rift occurred in

Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The J ...

to Late

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...

granite Granite () is a coarse-grained (phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies undergro ...

granodiorite Granodiorite () is a coarse-grained (phaneritic) intrusive igneous rock similar to granite, but containing more plagioclase feldspar than orthoclase feldspar. The term banatite is sometimes used informally for various rocks ranging from gra ...

intrusions.Nguyen Du Hung and Hung Van Le, ''Petroleum Geology of Cuu Long Basin - Offshore Vietnam'', Search and Discovery Article #10062 (2004), http://www.searchanddiscovery.net/documents/2004/hung/index.htm The fractured granitic rocks occur as a horst overlain and surrounded by Upper Oligocene

lacustrine A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much larger ...

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especial ...

source rock In petroleum geology, source rock is rock which has generated hydrocarbons or which could generate hydrocarbons. Source rocks are one of the necessary elements of a working petroleum system. They are organic-rich sediments that may have been depos ...

s. Bạch Hổ is not the only oil field convincingly shown to be hosted in granite;http://www.geoscience.co.uk/geofrc/geobaseasia.html Basement reservoirs in Asia however, inspection of the seismic profile of the area shows faulted basement passive margin which is sealed by an onlapping

sedimentary Sedimentary rocks are types of rock (geology), rock that are formed by the accumulation or deposition of mineral or organic matter, organic particles at Earth#Surface, Earth's surface, followed by cementation (geology), cementation. Sedimentati ...

sequence. It is plausible that the oil has migrated laterally from the lowermost, mature sediments into the fault systems within the granite. The

seismic Seismology (; from Ancient Greek σεισμός (''seismós'') meaning "earthquake" and -λογία (''-logía'') meaning "study of") is the scientific study of earthquakes and the propagation of elastic waves through the Earth or through other ...

profile shows a definite basement horst with onlapping sedimentary

s, draped by a reservoir seal.http://www.aapg.org/explorer/2005/02feb/vietnamcuulong.cfm CuuLong This trap view would see the oil migrate up the horst bounding faults from the lower source units, into the trap unit draped over the top.

Mobil Mobil is a petroleum brand owned and operated by American oil and gas corporation ExxonMobil. The brand was formerly owned and operated by an oil and gas corporation of the same name, which itself merged with Exxon to form ExxonMobil in 1999. ...

struck oil in the Bạch Hổ field in February 1975, shortly before the

Fall of Saigon The Fall of Saigon, also known as the Liberation of Saigon by North Vietnamese or Liberation of the South by the Vietnamese government, and known as Black April by anti-communist overseas Vietnamese was the capture of Saigon, the capital of ...

. It was later developed by the joint Vietnamese-Russian entity

Vietsovpetro Vietsovpetro, headquartered in Vung Tau, Vietnam, is a joint Russian-Vietnamese enterprise for oil and gas exploration. According to the VNR500 (Top 500) ranking, Vietsovpetro is Vietnam's 8th largest company. It was established in 1981 under ...

in the 1980s and 1990s. Upon examination of the source rock and oil content, petrogeologists have emphasized that the oil's components indicate a

organic

facies In geology, a facies ( , ; same pronunciation and spelling in the plural) is a body of rock with specified characteristics, which can be any observable attribute of rocks (such as their overall appearance, composition, or condition of formatio ...

with lipid-rich, land-plant debris and fresh-water algal material, refuting theories of abiogenic origin in this area.

References

See also