Extraction and uses

Before becoming petrol and plastic, oil needs to undergo a very complex artificial production process which starts with the search for oil fields and, through the extraction, processing and transportation stages (often taking place in countries very far away from each other), it ends with the petrol available at the local gas station or the rubber hose at the shop round the corner. Drilling wells is the only way to assess the value of a field, i.e. the type and quantity of the hydrocarbons contained therein.

The search for new fields

The search for new field is very expensive, and therefore it must be carried out with great care. The initial information is obtained by studying aerial photographs made from planes or satellites, which provide a map of the surface rocks, using the Geographic Information System (GIS) mapping to integrate the data, and for the reconstruction of digital models of the ground. Subsequently, geochemistry, micropaleontology and petrography provide all the information that is required with regard to the physical and chemical characteristics of the rocks, their age and composition. When a potentially interesting area is located, a series of inquiries are necessary in order to classify the nature of the rocks and their geological structure in the deeper layers underground, many thousands of metres in depth.

Drilling of onshore oil wells

Drilling a well is a long and expensive, albeit simple, operation. Rocks are drilled with a rotating bit mounted at the end of a series (battery) of mutually screwed steel pipes (rods), which is extended as the well becomes deeper. The rods are supported by a 50-meter tall tower (derrick) and their rotation is ensured by a rotating plate operated by means of a dedicated electric engine. The bit is made of very hard material and, in some cases, equipped with components of synthetic diamond.

Offshore drilling

The need to transfer drilling and production facilities off the coasts, with the consequent difficulties in setting up a plant capable of enduring particular environmental conditions, has resulted in innovative and state-of-the-art offshore research and engineering as far as technological development is concerned.
Offshore facilities are of different types and differ depending on the seabed, water depth and the prevailing climatic conditions.

Oil rigs

The first offshore drilling operations took place in the Gulf of Mexico in the late 1930s. The first predecessors of modern offshore platforms were installed at the beginning of the Fifties, but it was not until the Seventies that the offshore industry really started booming. In the Eighties, there were advances in drilling technology for moderately deep sea exploitation, while in the Nineties, more attention was focused on oilfields of small dimensions (but not economically attractive) and on the search for deep sea hydrocarbon reserves.

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.

On extraction, crude oil contains a mixture of hydrocarbons along with water, dissolved natural gas, salts, sulphur and inert substances such as sand and heavy metals. Prior to being introduced into the pipelines, crude oil must undergo a number of processes such as degasification, dehydration, desalting and desulphurisation.

Treatment and storage

During the degasification stage, crude oil is separated from associated gas. In order to do this, crude oil is made to pass through a series of separators (3 or 4); separators are particular pressure vessels. This separation process in different stages allows the maximum recovery of liquid hydrocarbons.

The transport

Oil is present in sufficient quantities to start production only in certain areas of the world, therefore most of it needs to be transported to reach refineries and the place of consumption. In terms of transport, there are two complementary ways to transport oil: pipelines and oil tankers.

Refining

Crude oil includes a large range of hydrocarbons with different quantities of carbon atoms. The ratio of the components varies according to the place of origin. For example, the oil of Venezuela is rich in long molecules making it thicker, whereas the crude oil from the North Sea is more liquid. To subdivide crude oil into its components, while providing its optimum exploitation, a fractioned distillation (or refining or cracking) is necessary.

Vapour plants

In particular, thermoelectric plants exploit vapour energy, which is produced by a “boiler” that burns a liquid fuel, such as fuel oil and naphtha or methane (usually modern boilers can burn the three types of fuel without distinction). Usually large thermoelectric power plants are installed close to big consumption centres and need suitable water supplies for vapour production and fuel storage.

Turbogas plants

Another type of plant uses a gas turbine instead of a boiler. The gas turbine is a rotating thermal machine that converts the heat into work, by directly using combusted gases as working fluid, supplying mechanic power on a rotating shaft.

Decommissioning

When an oil field is depleted, the decommissioning of the production facilities follows. The activities carried out during the decommissioning phase include the safe removal of the pre-treatment plant, the platform structures, the compression structures and the hydrocarbon dispatch facilities and the removal of the wellheads and the pipelines that connect to the collection points. Following the dismantling of the production facilities, there is the environmental restoration phase.