Energy

Origins of oil

The most favourable environment for the formation of new hydrocarbons includes areas marked by a limited circulation at the bottom and constant accumulation of debris by rivers (ancient seas or lakes), as well as sedimentary basins where the Earth’s crust is lowered gradually or quickly following natural geological processes (see image). Those areas are inhabited by numerous organisms which, when they die, lye at the bottom and are constantly covered by the debris (soil and minerals). The layers of mud rich in organic substances (mother-rock) slowly sink owing to the pressure of new layers. At a given depth and temperature the organic substance “ripens”, at first turning into “Kerogen” (approximately 1000 metres and 50°C), then into actual hydrocarbons. The length of the process ranges from 10 to 100 million years according to the temperature. If the organic substances are abundant, remarkable fields of coal and natural gas can result. If the kerogen does not ripen, and its concentration exceeds 8%, liquid oil can be obtained by heating it artificially. At greater depth methane and light hydrocarbons are produced. Several kilometres away from the surface and at a temperature ranging from 150 to 200°C, kerogen turns into pure crystal carbon (graphite).