Oil Extraction

There are two types of oil- conventional and unconventional where conventional oil is the oil extracted and used today whilst unconventional oil is either very hard to extract, economically unprofitable to do so or requires more complicated expensive methods of conversion of the original product into the oil that we use in our every day lives such as petroleum. Conventional oil is extracted via wells, which are drilled into the ground by drilling a long hole into the ground using oilrigs. Large reservoirs require multiple wells as the wells only reach the top layers of the oil reservoirs. Modern technologies mean that wells can be not only vertical but also horizontal thus allowing oil to be extracted from the edges of the reservoirs and decreasing the number of wells required per each reservoir. A steel pipe is placed into each hole that is dug into the ground to make the corridor to the well more straight and stable. Holes are made in the base of the well to enable oil to pass into the bore. A collection of valves is fitted to the top in order to regulate pressures and control the flow of oil. These valves are known as “Christmas Tree”.

Figure 1.

Source. Helicopters at oil rigs in the North Sea, Scotland.

There are three methods of oil recovery from the wells once the rigs have been put in place. First is primary recovery, which uses the fact that oil initially flows to the surface under its own pressure. Around 10-15% (Miller, 2013)  of the original oil in the reservoir can be removed using this natural method that does not require much effort. This is known as easy oil and most of this oil has now been extracted. Once the pressure starts to weaken, artificial lift mechanisms such as pumps and electrical submersible pumps (ESPs) or injecting water or gases into the field to maintain pressure are used to bring oil to the surface. This allows a further 35% of the reservoir oil to be extracted this way. (Miller, 2013). After a while a lot of dissolution of oil is seen and more water is actually being pumped out of the wells rather than oil so it becomes uneconomic to continue extraction so the rigs are either abandoned or enhanced oil recovery (EOR) techniques, also known as tertiary recovery are used. They increase the percentage of oil extracted from the reservoir by a further 5-15% with the ultimate results reaching recovery factors of over 70%. Tertiary recovery involves the use of steam injection, CO2 injection and chemical flooding with the aim to reduce oil viscosity thus preventing the unwanted flows of gases and water and pushing oil towards wells and hence the surface.

A more eco-friendly tertiary approach involves microbial treatments, which uses microbes to treat and break hydrocarbon chains in oil so it becomes possible to recover it. This method is very economically profitable in comparison to traditional approaches too. It is not widely used however governments such as that of the USA try to promote it by putting in place tax incentives (e.g. those seen in Texas) for using the microbes although there are still not many companies that even supply the microbes in the first place, Bio Tech being one of the few.