Energy

Capacious reservoir

Reservoir rocks must have an elevated porosity and permeability: the higher these values are, the greater the quantity of hydrocarbons that the reservoir rock can contain and the easier it will be to extract oil and gas. Naturally, the greater the volume of the reservoir rock, the greater the volume of the oil field. The most efficient reservoir rocks are the ‘silicoclastic’ ones, made up of granules and fragments of pre-existent rocks (sand, sandstone, conglomerate). These rocks are characterized by an elevated porosity and form high quality basins. It has been calculated that 60% of the oil fields discovered up to now are contained in rocks of this type. Even carbonate rocks (calcareous and dolomite) are good reservoir rocks when they are intensely fractured or of organic origin (such as coastal calcareous rocks), when karst processes are active and create big underground void spaces. A little less than 40% of the world oil fields is contained in rocks of this kind. All other kinds of rocks make good reservoirs only when they are intensely fractured: generally, they contain very small oil fields that are therefore practically irrelevant, Important fields in fractured granite rock can only be found in the area between Kansas and Texas (Anadark basin), in the Egyptian field of Ashrafi, in the Gulf of Suez and in the off-shore field of Bach-Ho, in Vietnam.