Energy

Transformation of organic material

The sediments that are progressively deposited bury the ones below, that are therefore covered by growing layers of material that accumulate in time. As they are pushed deeper and deeper in the Earth’s crust, the sediments slowly loose the water that they contained originally, become denser and more compact and are subjected to growing temperature and pressure. The ‘oil window’ is defined as the set of particular pressure and temperature conditions that are required for the transformation of organic material into hydrocarbons. For an important oil-yielding province to be formed, it is also necessary that the mother rock should reach the conditions of an ‘oil window’. The transformation can take place at low temperatures but over a long lapse of time (as in older rocks) or in a short time but with higher temperatures (as in younger rocks): the age of the mother rock is not a determining factor in the production of hydrocarbons but the temperature it reaches is. The initial characteristics of the organic substance in addition to the conditions and the time required to reach the ‘oil window’ can be decisive to determine a greater production of gas rather than oil. The researchers carry out a series of tests on the possible mother rocks to establish whether these have reached the conditions that are necessary for transformation, or not, by checking some specific ‘indices’: the reflecting power of vitrinite (an organic substance that increases, reflecting the higher the temperature to which it is subjected) and the colour of pollen spores (that become darker as the temperature rises).