school energy&environment

Oil fields in the world

The distribution of the principal oil fields in the world is not uniform, but neither is it random, and it depends on particular geological conditions that are necessary for the formation of large reserves and the difficulty of exploring and researching oil in isolated areas that are not well known, such as areas characterized by particularly severe environmental conditions (the vast areas of Siberia, the areas of the rain forest in South America and the deep offshore areas). The more important oil fields have geological characteristics that are very different from each other, but they have some common elements.
According to the above stated considerations, the first areas in which to search for hydrocarbons are the areas in which sea sediments are present, where the seas are not very deep and are rich in organic substances developing in anoxic environments, which are the ideal mother rocks for hydrocarbons. These conditions are to be found in the fields that are near to stable continental areas (the so-called cratons), where detritus sediments coming from the emerged lands form powerful and thick deposits of permeable material (reservoir rock) covered with fine marine deposits (cap rock).  For this reason, many of the more productive fields are to be found along the borders of the continents: in the North American fields in Texas and Louisiana, in the Gulf of Mexico, in the Mexican fields in Tampico-Misantla and Sureste, in the Central African fields of the Niger delta and the Congo Basin and the enormous fields  in Western Siberia.
Similar situations with longer, narrower fields also form in the rifts along the borders of subduction areas. In these areas the tectonic deformations can create efficacious structural traps, as in the Venezuelan fields along the Andes mountain range or as in the Sumatra field. Also deep fields characterized by a rapid sedimentation  are favourable regions for the formation of important reserves, as for example in Europe in the small province of the Rhine basin or in Graben in the North Sea, that are the most important reserves in Western Europe. Also the large Sirte field in Libya has a similar origin.
However, it is in the continental collision areas, that lead to the formation of mountain ranges, that  the more favourable situations for the formation of numerous and important structural traps are generally found. In these areas the reserves are very often numerous and their volume is large. The enormous oil fields in the Middle East, that are the most extensive and important in the world, follow the trend of the mountain ranges that were formed from the collision of the Euro-Asiatic plate and the Arabian plate.
Also the large fields of the Volga and the Urals, are in a continental suture area, but they belong to a more ancient orogenetic cycle. The collision of the African plate and the European plate in the Mediterranean area, created numerous mountain ranges, among which the Pyrenees, the Alps and the North-African ranges. Near these areas, in particular in the accumulation reservoirs on the front of the mountain range, we find the largest Mediterranean oil fields, such as the Sahara field, but also the largest Italian oil provinces (such as the Po valley, the Adriatic coast, South East Sicily and the Sicily Channel).Important reserves are also to be found, all over the world, in areas where the presence of levels of evaporitic rocks has led to the formation of  diapiric salt as for example in many reserves in Central Europe and in the area around the Gulf of Mexico.