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Size distribution of oil fields
Oil has been explored for and pumped from the earth for well over a century and the results have been impressive: over 41 thousand oil fields have been discovered worldwide. By no means are all of these fields of comparable size, however. (See the Table.)
| Table. Distribution of World Oil Fields by Size |
| EUR (million barrels) |
Size |
United States |
World Total |
| 50,000+ |
Megagiant |
None |
2 |
| 5,000 - 50,000 |
Supergiant |
2 |
40 |
| 500 - 5,000 |
Giant |
46 |
328 |
| 100 - 500 |
Major |
240 |
961 |
| 50 - 100 |
Large |
327 |
895 |
| 25 - 50 |
Medium |
356 |
1,109 |
| 10 - 25 |
Small |
761 |
2,128 |
| 1 - 10 |
Very small |
4,599 |
7,112 |
| 0.1 - 1 |
Tiny |
9,533 |
10,849 |
| 0 - 0.1 |
Insignificant |
11,021 |
11,751 |
| 0 - 0.5 |
Other tiny |
4,500 |
5,989 |
| Total |
31,385 |
41,164 |
| Source: L.F. Ivanhoe and G.G. Leckie, "Global Oil, Gas Fields, Sizes Tallied, Analyzed," Oil & Gas Journal, February 15, 1993, pp. 87-91. |
Of the fields found so far:
- Three quarters (31,000) are in the United States while only 537 are in the Middle East.[1]
- Both of the two Megagiant fields (more than 50 billion barrels ultimately recoverable) are in the Middle East, one in Saudi Arabia and one in Kuwait.
- Of the forty Supergiant fields (containing between 5 billion and 50 billion barrels) discovered, one is in Alaska and one is in the lower 48 United States.
- Of the 328 Giant fields (500 million to five billion barrels) found, 46 are in the United States.
The importance of the gigantic oil fields in global oil supply cannot be overemphasized.
- The 370 known oil fields containing 500 million barrels or more account for an estimated three quarters of all recoverable oil but less than one percent of the total number of fields.[2]
- The 1331 largest discovered oil fields -- each containing 100 million barrels or more of ultimately recoverable oil -- account for 94 percent of all discovered oil but only 3 percent of all oil fields.
At the other end of the spectrum, the 39,833 smaller fields contain only 6 percent of the crude oil that will ultimately be recovered.
The implications of this skewed distribution are aptly summarized by Riva:
"... most oil is contained in a few large fields, but most fields are small...as exploration progresses, the average size of the fields discovered decreases as does the amount of oil found per unit of exploratory drilling. In any region, the large fields are the biggest targets and are usually discovered first."[3]
In other words, exploration in the declining phase of oil development is a far different game than in the early phase. In the early stages, it is the large fields that are readily discovered; in the declining stages, geologists are much more likely to find small fields and oil companies must do a lot more drilling just to stay even.
Notes
1. L.F. Ivanhoe, and George G. Leckie, "Global Oil, Gas Fields, Sizes Tallied, Analyzed," Oil & Gas Journal, February 15, 1993: 87-91.
2. L.F. Ivanhoe, and George G. Leckie, "Global Oil, Gas Fields, Sizes Tallied, Analyzed," Oil & Gas Journal, February 15, 1993: 87-91.
3. Joseph P. Riva, "Oil Distribution and Production Potential," Oil & Gas Journal, January 18, 1988: 58-61.
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