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 prese ...

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

Mekong Delta The Mekong Delta ( or simply ), also known as the Western Region () or South-western region (), is the list of regions of Vietnam, region in southwestern Vietnam where the Mekong, Mekong River River delta, approaches and empties into the sea th ...

Vietnam Vietnam, officially the Socialist Republic of Vietnam (SRV), is a country at the eastern edge of mainland Southeast Asia, with an area of about and a population of over 100 million, making it the world's List of countries and depende ...

. 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-graben ...

zone developed during the

Oligocene The Oligocene ( ) is a geologic epoch (geology), epoch of the Paleogene Geologic time scale, Period that extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that defin ...

to Early

Miocene The Miocene ( ) is the first epoch (geology), 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 mea ...

. 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 143.1 Mya. ...

to Late

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

granite Granite ( ) is a coarse-grained (phanerite, phaneritic) intrusive rock, 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 coo ...

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 often a naturally occurring, relatively large and fixed body of water on or near the Earth's surface. It is localized in a basin or interconnected basins surrounded by dry land. Lakes lie completely on land and are separate from t ...

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of Clay mineral, clay minerals (hydrous aluminium phyllosilicates, e.g., Kaolinite, kaolin, aluminium, Al2Silicon, Si2Oxygen, O5(hydroxide, OH)4) and tiny f ...

source rock In petroleum geology, source rock is a sedimentary rock which has generated hydrocarbons or which has the potential to generate hydrocarbons. Source rocks are one of the necessary elements of a working petroleum system. They are organic-rich sedim ...

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 formed by the cementation of sediments—i.e. particles made of minerals (geological detritus) or organic matter (biological detritus)—that have been accumulated or deposited at Earth's surface. Sedime ...

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 (or generally, quakes) and the generation and propagation of elastic ...

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 Oil Corporation, now known as just Mobil, is a petroleum brand owned and operated by American oil and gas corporation ExxonMobil, formerly known as Exxon, which took its current name after history of ExxonMobil#merger, it and Mobil merge ...

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

Fall of Saigon The fall of Saigon, known in Vietnam as Reunification Day (), was the capture of Saigon, the capital of South Vietnam, by North Vietnam on 30 April 1975. As part of the 1975 spring offensive, this decisive event led to the collapse of the So ...

. It was later developed by the joint Vietnamese-Russian entity Vietsovpetro 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 distinctive characteristics. The characteristics can be any observable attribute of rocks (such as their overall appearance, composition, or con ...

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

References

See also