Energy

The extraction

In terms of extraction and processing, during the production stage a sufficient number of wells is drilled to maximise the exploitation of the oil field. Every day, over a period of approximately 20-30 years, a well produces between 500 and 1,000 tonnes of oil (a few thousand barrels) and a few hundred thousand cubic metres of natural gas. Initially, the oil flows up the pipes owing to the pressure of the water and the gas contained in the field. Thus, 30% of the oil and 90% of the natural gas are extracted. An additional 10-15% can be extracted by keeping up the pressure and adding more water or gas. Finally, an additional 10-15% can be extracted by injecting emulsions, steam or solvents washing the rocks and removing more oil. Approximately 1/5 of the world production of oil comes from the sea, a percentage bound to increase in the next years. In this case, during the first stages many wells are drilled a few meters away from each other. Then, to drain all the fields, also horizontally, the wells are deviated to reach locations up to a few kilometres away from each other. If the sea bottom is more than 400-metre deep, undersea plants are necessary and the opening of the well is on the sea bottom.