4.2 Sedimentary basins

Giant petroleum fields and significant petroleum-producing sedimentary basins are closely associated. In some basins, huge amounts of petroleum apparently have been generated because perhaps only about 10 percent of the generated petroleum is trapped and preserved. The Arabian-Iranian sedimentary basin is predominant because it contains more than 20 supergiant fields. No other basin has more than one such field. In 20 of the 26 most significant oil-containing basins, the 10 largest fields originally contained more than 50 percent of the known recoverable oil. Known world oil reserves are concentrated in a relatively small number of giant fields in a few sedimentary basins.

Worldwide, approximately 600 sedimentary basins are known to exist. About 160 of these have yielded oil, but only 26 are significant producers and 7 of these account for more than 65 percent of total known oil. Exploration has occurred in another 240 basins, but discoveries of commercial significance have not been made.

4.3 Geologic study and exploration

Current geologic understanding can usually distinguish between geologically favourable and unfavourable conditions for oil accumulation early in the exploration cycle. Thus, only a relatively few exploratory wells may be necessary to indicate whether a region is likely to contain significant amounts of oil. Modern petroleum exploration is an efficient process. If giant fields exist, it is likely that most of the oil in a region will be found by the first 50 to 250 exploratory wells. This number may be exceeded if there is a much greater than normal amount of major prospects or if exploration drilling patterns are dictated by either political or unusual technological considerations. Thus, while undiscovered commercial oil fields may exist in some of the 240 explored but seemingly barren basins, it is unlikely that they will be of major importance since the largest are normally found early in the exploration process.

The remaining 200 basins have had little or no exploration, but they have had sufficient geologic study to indicate their dimensions, amount and type of sediments, and general structural character. Most of the underexplored (or frontier) basins are located in difficult environments, such as Polar Regions or submerged continental margins. The larger sedimentary basins—those containing more than 833,000 cubic kilometres (200,000 cubic miles) of sediments—account for some 70 percent of known world petroleum. Future exploration will have to involve the smaller basins as well as the more expensive and difficult frontier basins.

1. Make up sentences and translate them

1. To, worldwide, 600, basins, approximately, sedimentary, are, exist, known.

2. Associated, and, petroleum-producing, giant, closely, petroleum, significant, sedimentary, fields, are, basins.

3. An, modern, is, process, exploration, efficient, petroleum.

2. Add the sentences and translate them

1. Known world oil reserves are concentrated in a relatively small number of………. .

2. Exploration has occurred in another 240 basins, but discoveries of …….. .

3. Future exploration will have to involve the smaller basins as well as ……. .

4. More than 90 percent of these fields are insignificant in ……. .

5. In any region, the large fields are …….. .

6. The Arabian-Iranian Sedimentary basin in the Persian Gulf region contains two-thirds of …….. .

7. These fields account for some 14 to 16 percent of ……. .

( the world’s known oil; commercial significance have not been made; giant fields in a few sedimentary basins; the more expensive and difficult frontier basins, these supergiant fields; their impact on world oil production; usually discovered first)