Oil fields

Once it has formed, oil is squeezed out of the mother rock (compressed by the layers lying on top) and it first moves through the microfractures (primary migration) and then into the small channels in the permeable adjacent rocks (secondary migration). In some cases hydrocarbons reach the earth’s surface and disperse. In others, their migration is blocked by impermeable rocks. In this case the hydrocarbons are trapped and they accumulate. An accumulation of hydrocarbons, in a quantity that can be exploited economically is known as a field.
A trap consists of two elements: below, a reservoir rock that holds the petroleum and above, a cap rock that forms a barrier. Cap rocks are convex on the upper side and are impermeable, so that they prevent the hydrocarbons from escaping. On the contrary the reservoir rocks must be permeable and porous like sponges in order to enable the hydrocarbons to move within, and to make the extraction procedures easy. The size of a deposit depends on the amount of the original reserve – from the over 11 billion tons in the Ghawar deposit (Saudi Arabia) to a few hundred tons in the smaller fields.

Special reports

From the Multimedia section

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    Classification of reservoirs

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    World oil reserves at 2018

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    Laying of a pipeline

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    Pipeline under construction

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    Men at work

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    Drilling of wells

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    Classification of reservoirs

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    World oil reserves at 2018

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    Laying of a pipeline

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    In order to improve supply security, and therefore the diversification of sources to produce electric energy...

    Cracking operations

    At the end of the fractional distillation, long hydrocarbon molecules can be transformed into lighter molecules by means of more…

  • Where does energy come from?

    Every day the Earth receives enough solar energy to satisfy the global energy need...

    Electricity and electrons

    In all electric plants, excluding photovoltaic solar plants, mechanic energy is transformed into electric energy through the same basic procedure...

  • Peat and peat-bogs

    The age of coal starts towards the mid 1600s, stimulated by the need for finding an alternative energy source to…

    Geographical distribution of energy

    Every day the Earth receives enough solar energy to satisfy the global energy need. Unfortunately we cannot exploit all this…

  • Orimulsion

    In order to improve supply security, and therefore the diversification of sources to produce electric energy...

  • Cracking operations

    At the end of the fractional distillation, long hydrocarbon molecules can be transformed into lighter molecules by means of more…

  • Where does energy come from?

    Every day the Earth receives enough solar energy to satisfy the global energy need...