Ghawar
the largest oil field in the world
The Ghawar field in Saudi Arabia is the largest oil field in the world.
It was discovered in 1937 and is located about 100 kilometers from the city of Dhahran, in the Eastern Province of that country ..
It occupies an area of ​​8,400 square kilometers (280 kilometers long and 30 kilometers wide).
This site is currently capable of producing 3.8 million barrels of oil per day, which represents almost 5% of world production and 65% of Saudi production. It also produces about 2 billion cubic feet of natural gas a day.
Since its production began in 1951, about 60,000 million barrels have been extracted.
According to oil company Saudi Aramco, owner of Ghawar, it is still the largest oil field in the world.
Although its production level is reduced between 2% and 8% each year, there are a recoverable reserves of just over 70,000 million barrels.
Geology
The Ghawar oilfield is constituted by an anticline structure (convex fold) that is expressed on the surface by outcropping of tertiary rocks (relatively more modern).
To the north, this structure comprises two parallel anticline (convex folds) with a small depression between them.
The Ghawar anticline rests on a horst (raised block) of the crystalline basement that initially ascended during the carboniferous period (300 million years) and was reactivated, episodically, especially during the late Cretaceous (100 million years).
The Paleozoic section (ancient, at the base) was significantly eroded by Hercinian discordance (that is, erosion that occurred about 280 to 250 million years ago).
The structure is asymmetric, steeper to the west and becomes more complex in depth, where there are several horst (raised blocks) in the form of stairs.
The main reservoir of Ghawar is the Jurassic limestones (160-180 million years old) that are somewhat less than 100 meters thick and are 2,000-2,300 meters below the surface.
The deposition of calcareous rocks included grainy (marine) reefs in the north, improving the quality of the reservoir, which also improves upwards as it evolves from a relatively massive limestone limestone to a grainy skeletal oolithic limestone (oolites are micro-concretions spherical). The density of fractures increases with depth, increasing the permeability of fine grain limolites.
According to the most accepted hypothesis, oil comes from Jurassic limestone limolites, which were deposited in the inner basins of the shield. It is important to note that given the immense and sustained volumes of production it would be necessary to start considering its origin from deeper, non-biogenic levels.
The upper seal of the deposit is constituted by anhydrides and is favored by the general absence of failures in the Jurassic section.
In summary, if the biogenic origin is accepted, there would be a Jurassic mother rock (Hanifa formation) covered by the powerful and porous Arab-D reservoir and an anhydritic upper seal. In other words, a great structure with an appropriate thermal and dynamic history.
The abundant production of the deposit was favored through the injection of water that was initiated in 1965. The volumes of seawater injected have reached 7 million barrels per day
In addition to oil, the field produces about 2,000 million cubic feet of gas per day, and has the capacity to extract 5,500 million cubic feet of gas from the deep section of the Paleozoic (more than 200 million years) that are trapped in the reservoirs Permian, permo-carboniferous and devonic (that is, between 380 and 200 million years old). Apparently this gas would come from siluric shales (if the biogenic origin is accepted). The possibility of a deeper non-biogenic origin should also be taken into account.
Khuff Permian Calcareous Reservoirs are the main gas producing areas at depths of 3,000 to 4,000 meters.
In short, it is a sedimentary sequence of several thousand years with excellent storage conditions for hydrocarbons and a geological source that has supplied huge volumes of liquid hydrocarbons and natural gas from deeper levels. It is assumed that these levels are sedimentary and organic, but should not be excluded, following the theory of Thomas Gold, given the huge amount of accumulated hydrocarbons and their sustained production for a long time, which are of much deeper non-biological origin.