Describe the Geological Factors for the Formation and Accumulation of Economic Quantities of Oil and Natural Gas.

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Describe the geological factors for the formation and accumulation of economic quantities of oil and natural gas. For an economic accumulation of oil and natural gas to form there need to be six requirements. These are for there to be a source rock, maturation, migration, a reservoir rock, a cap rock and a trap. First of all the oil and natural gas if formed when marine plankton die and sink down to deep marine basins. There plankton is then buried and compacted under the different layers of sediment being deposited, this is the source rock. The source rock must be a fine grained, organic rich sedimentary rock. These source rocks are black oil shale and mudstone which are very dark in colour due to the high amount of organic carbon content. These mudstones and shale’s are fine grained due to the low energy environment. As the source rock goes under further compaction, due to the geothermal gradient the temperature increases. Gradually over time the organic matter breaks down to form a mixture of organic compounds of carbon, hydrogen, oxygen, nitrogen and sulphur called Kerogen and then petroleum. This is the process of maturation. Petroleum will form between the temperatures of 50 to 200 degrees. This temperature range is known at the ‘oil window’. Below 50 degrees biogenic gas forms but due to a shallow burial this gas is usually lost. Most oils will form between 50 to 100 degrees and natural gas is also produced mainly consisting of methane will form at 100 to 200

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