Giant oil and gas fields

Giant oil and gas fields

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The world's 932 giant oil and gas fields are considered those with 500 Moilbbl of ultimately recoverable oil or gas equivalent. Geoscientists believe these giants account for 40 percent of the world's petroleum reserves. They are clustered in 27 regions of the world, with the largest clusters in the Persian Gulf
Persian Gulf
The Persian Gulf, in Southwest Asia, is an extension of the Indian Ocean located between Iran and the Arabian Peninsula.The Persian Gulf was the focus of the 1980–1988 Iran-Iraq War, in which each side attacked the other's oil tankers...

 and Western Siberian Basin. The past three decades reflect declines in discoveries of giant fields. The present decade (2000–2011), however, reflects an upturn in discoveries and appears on track to be the third best for discovery of giant oil and gas fields in the 150 year history of modern oil and gas exploration.

According to analysis led by Paul Mann of the University of Texas' Jackson School of Geosciences
Jackson School of Geosciences
The Jackson School of Geosciences at The University of Texas at Austin unites the Department of Geological Sciences with two research units, the Institute for Geophysics and the Bureau of Economic Geology....

, almost all of the 932 giant oil and gas fields cluster within 27 regions, or about 30 percent of Earth's land surface. Since 2003, Mann and colleagues M.K. Horn and Ian Cross have tracked the giants on a map that highlights the tectonic and sedimentary basin maps of the 27 key regions. The map is in the public domain and available as a high-resolution pdf on the Web site of the Jackson School of Geosciences.

Recent work in tracking giant oil and gas fields follows the earlier efforts of the late exploration geologist Michel T. Halbouty
Michel T. Halbouty
Michel Thomas Halbouty was an American geologist, petroleum engineer, and wildcatter. Credited with discovering more than 50 oil and gas fields, he twice declared bankruptcy, but came back each time to regain wealth...

, who tracked trends in giant discoveries from the 1960s to 2004.

Tectonic settings


Geophysicists and exploration geologists who look for oil and gas fields classify the subsurface characteristics, or tectonic setting, of geological structures that contain hydrocarbons. Any one oil and gas field may reflect influences from multiple geological periods and events, but geoscientists often attempt to characterize a field based on the dominant geological event that influenced the structure's ability to trap and contain oil and gas in recoverable quantities.

A majority of the world's giant oil and gas fields exist in two characteristic tectonic settings—passive margin
Passive margin
A passive margin is the transition between oceanic and continental crust which is not an active plate margin. It is constructed by sedimentation above an ancient rift, now marked by transitional crust. Continental rifting creates new ocean basins. Eventually the continental rift forms a mid-oceanic...

 and rift environments. Passive margins are found along the edges of major ocean basins, such as the Atlantic coast of Brazil where oil and gas has been located in large quantities in the Campos basin. Rifts are oceanic ridges formed when tectonic plates separate and a new crust is created. The North Sea is an example of a rift setting associated with prodigious hydrocarbon reserves. Geoscientists theorize that both zones are especially conducive to forming giant oil and gas fields when they are distant from active tectonic areas. Stability appears to be conducive to trapping and retaining hydrocarbons under the subsurface.

Four other common tectonic settings, including collisional margins, strike-slip margins, and subduction margins, are associated with the formation of giant oil and gas fields, though not to the dominant extent of passive margin and rift settings.

Recent and future giants


Based on the locations of past giants, Mann et al. predicted new discoveries of giant oil and gas fields would mainly be made in passive margin and rift environments, especially in deepwater basins. They also predicted that existing areas that have produced giant fields would be likely targets for new discoveries of "elephants," as the fields are sometimes known in the oil and gas industry.

Data from 2000-2007 reflect the accuracy of their predictions. The 79 new giant oil and gas fields discovered from 2000-2007 tended to be located in similar tectonic settings as the previously documented giants from 1868–2000, with 36 percent along passive margins, 30 percent in rift zones or overlying sags (structures associated with rifts), and 20 percent in collisional zones.

Despite a recent uptick in the number of giant oil and gas fields, discovery of giants appears to have peaked in the 1960s and 1970s. Looking to the future, geoscientists foresee a continuation of the recent trend of discovering more giant gas fields than oil fields. Two major continental regions—Antarctica and the Arctic
Arctic
The Arctic is a region located at the northern-most part of the Earth. The Arctic consists of the Arctic Ocean and parts of Canada, Russia, Greenland, the United States, Norway, Sweden, Finland, and Iceland. The Arctic region consists of a vast, ice-covered ocean, surrounded by treeless permafrost...

—remain largely unexplored. Beyond them, however, trends suggest that remaining giant fields will be discovered in "in-fill" areas where past giants have been clustered and in frontier, or new, areas that correspond to the predominant tectonic settings of past giants.

Giant field production properties and behaviour


Comprehensive analysis of the production from the majority of the world's giant oil fields has shown their enormous importance for global oil production. For instance, the 20 largest oil fields in the world alone account for roughly 25% of the total oil production. The majority of the world's giants are already in decline and this will have dramatic consequences for future oil supply.

Further analysis shows that giant oil fields typically reach their maximum production before 50% of the ultimate recoverable volume has been extracted. A strong correlation between depletion and the rate of decline was also found in that study, indicating that much new technology has only been able to temporarily decrease depletion at the expense of rapid future decline. This is exactly the case in the Cantarell Field
Cantarell Field
Cantarell Field or Cantarell Complex is an aging supergiant oil field in Mexico. It was discovered in 1976 by a fisherman, Rudesindo Cantarell. It was placed on nitrogen injection in 2000, and production peaked at in 2003. In terms of cumulative production to date, it is by far the largest oil...

.

See also


  • Hydrocarbon exploration
  • List of countries by oil proven reserves
  • List of natural gas fields
  • Oil megaprojects
    Oil megaprojects
    -Megaprojects predicted for individual years:-New supply addition per country from oil megaprojects:Volumes shown are in thousand barrels per day. The summary table below is produced by a Perl script parsing each annual table...

  • Peak oil
    Peak oil
    Peak oil is the point in time when the maximum rate of global petroleum extraction is reached, after which the rate of production enters terminal decline. This concept is based on the observed production rates of individual oil wells, projected reserves and the combined production rate of a field...

  • List of largest oil fields

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