Sometimes, the escape of gaseous or liquid hydrocarbons through cracks in the ground, or the identification on the surface of traces indicating the presence of fossil fuels such as asphalt, for example, facilitate the investigation task. Usually, it is necessary to carry out complex and expensive studies that only in 10% of the cases manage to discover oil, and only 0.2% of which are rich enough to be exploited profitably.
The most diverse and modern sciences and technologies participate in the search for new deposits. It works by analyzing aerial and satellite photographs, which allow the reconstruction of the internal structure of the terrain, the variations in the terrestrial magnetic and gravitational field are studied, or the characteristics of the stones collected by geological surveys are analyzed with X-rays. With the information obtained, a geological map of the place is drawn, the first step in oil exploration.
One of the most widely used methods is the study of the characteristics of the underground layers, through seismic waves caused artificially. This system is based on the study of the behavior of a sound wave when it crosses or bounces in the subsoil strata. The waves are collected by highly sensitive seismographs located on the surface - the same devices used to detect earthquakes - and the data is analyzed in a computer. The propagation speed of the waves makes it possible to determine the structure of the terrain, the existence of hard layers and their depth. The operation is repeated several times from different locations to produce a detailed map of the depths.
Once the prospecting phase is finished, a survey is carried out to find out if a well contains enough oil to make its exploitation profitable.
This survey is carried out with a very powerful drill installed in a drilling tower, which slowly bores holes into the ground, until it reaches the point where the deposit is. As the drill progresses, tubes are placed through which the oil will be driven to the surface. In cases where the survey is carried out at sea, special platforms or boats are used, equipped with all the necessary elements to carry out the surveys.
When, finally, the layer that contains oil is accessed, one must work very carefully when extracting it, since extremely high pressures are released that must be controlled to avoid leaks and explosions. Once the well has been opened, the tower is removed, a pumping machine is installed and the extraction of crude oil begins. Thus begins the journey of oil that will take it to all parts of the planet and will make its derivatives one of the most precious consumer goods for today's civilization.
In Spain, hydrocarbon exploration operations began in 1941 without success. The first positive result occurred in 1960. Near Vitoria, a small accumulation of natural gas was found. In 1964, the first oil deposit in Spain was discovered, Ayoluengo in La Lora (Burgos), reaching a production of 1000 barrels per day of very poor quality.
In 1970, the offshore deposit of Tarragona de Amposta was discovered and, in 1975, that of Casablanca. In relation to natural gas, in 1978 a deposit was discovered in Jaca and another in the Gulf of Cádiz. In 1980, another gas field was found off Bermeo.