The history of oil in the Middle East is essentially a story of giant oil fields (each containing over 500 million barrels).
Of the 932 known giants that researchers at the University of Texas in Austin have mapped, over 200 are located in the Persian Gulf region, which accounts for about 2 percent of Earth’s land area – and the “Elephant of All Elephants” (AAPG EXPLORER, January 2005) is Saudi Arabia’s Ghawar field.
Discovered in 1948, Ghawar started to produce oil in 1951 – 60 years ago – but to this day it remains the world’s richest and most productive oil field.
Today the oil industry in Saudi Arabia is in full control of a state-run company, Saudi Aramco. The company’s origin, however – as well as the history of oil discovery in the kingdom – dates back to the Arabian American Oil Company (Aramco).
The first oil field discovered in Saudi Arabia was not Ghawar but Dammam, in March 1938, followed by Abu Hadriyah (March 1940) and Abqaiq (December 1940). These fields are located in the Eastern Al Hasa region where pioneering mapping began by American geologists in the early 1930s.
The legendary Max Steineke and Tom Kock, both AAPG members with California Arabian Standard Oil Co. (Socal) in 1935 first spotted topographic indications of the En Nala anticline on which Ghawar sits.
In 1940, Ernie Berg, a young Aramco geologist who was mapping areas near the Abqaiq field, noted that the Wadi Sahaba, a seasonal river valley in the Haradh area, took a sudden bend from its east-west direction toward the south.
Berg related this wadi diversion to a north-south trending subsurface anticline. Steineke, his boss, supported the idea.
Shallow structural-stratigraphic drillings in the desert (a technique Steineke had developed to map the subsurface geology and collect pre-Neogene information) confirmed the existence of what came to be called the En Nala (“the Slippers”) anticline.
After World War II, exploration resumed on the Arabian Peninsula, and the information from shallow drillings were supplemented with gravity and magnetic surveys. The En Nala anticline was thus better imaged.
This“whale back” structure, about 280 kilometers long and 30 kilometers wide on average, contains six major structural culminations; from north to south, they are Fazran, Ain Dar, Shedgum, Uthmaniyah, Haradh and Hawiyah.
In 1948 Aramco drilled a test well at Ain Dar, which hit oil in June, marking the first post-war discovery in the kingdom. In a letter dated July 6, 1948, S.V. Campbell, an Aramco manager, reported the good news to the Saudi finance minister Shaikh Abdullah Sulaiman:
“In a 20-minute test at 6,685 to 6,746 feet, gas in the Ain Dar well rose to the surface in six minutes and oil rose to the surface in 11 minutes.”
More wildcats on the anticline, Haradh No. 1 (February 1949), Uthmaniyah No. 1 (April 1951), Shedgum No. 1 (August 1952) and Hawiyah No. 1 (1953) all discovered light crude (32-36° API) from the Upper Jurassic carbonate reservoir (the 100-meter Arab-D member) at depths of 2,000-2,330 meters.
By 1953, the geologists recognized that all these prospects were actually parts of a single field; they named it Ghawar, after the wide pastoral landscape that local Bedouins called Al Ghawar.
The northernmost part of the supergiant, Fazran, was discovered in 1957. By then 129 wells were producing 0.6 million barrels of oil per day. Except for Uthmaniyah No. 1, all the other discovery wells at Ghawar still produce oil.
The first detailed report about Ghawar by the Aramco geologists was presented at the AAPG convention in Los Angeles in March 1958 and published in AAPG BULLETIN in February 1959 – a report that, amazingly, remains the cornerstone of our knowledge of this field.
In the 1970s, deeper drillings in the Ghawar field discovered enormous volumes of natural gas from the Permian carbonates of the Khuf Formation.
Public knowledge about the world’s largest field ironically remains scanty. This has led to speculative debates about Ghawar’s peak production and near-future demise – for example, Matthew Simmon’s 2006 book Twilight in the Desert.
AAPG member Abdul Kader M. Al-Afifi, a senior geologist with Saudi Aramco, reported in his 2004 AAPG Distinguished Lecture that Ghawar produced 4.6-5.2 MMbopd from 1993 through 2003.
The Ghawar anticline is draped over a basement horst, which started to develop during the Late Carboniferous extensional uplift in the region, which, in turn, eroded the middle Paleozoic sediments at Ghawar. Bounding normal faults have throws as much as 3,000 feet at the Silurian level, but they die out in the Triassic section, according to Afifi, who is past president of the AAPG Middle East Region (AAPG EXPLORER, January 2005).
The Cenozoic anticline at Ghawar, called the En Nala structure, is asymmetrical with a steeper western flank, and a minor component of right lateral strike slip.
The oil at Ghawar was sourced from Jurassic organic-rich marlstone.
The producing oil reservoir is the late Jurassic Arab-D limestone, which is about 280 feet thick and occurs 6,000-7,000 feet beneath the surface. Afifi also noted that reactivation of the structure during Arab-D deposition localized grain-dominated shoals in the north, upgrading the quality of the reservoir, which improves upward as it progresses from lime mudstone to skeletal oolitic grainstone.
Fracture density increases going deeper in the section, enhancing permeability in the finer-grained mudstones and carbonates.
Overall, 50-60 percent of Saudi oil production has historically come from Ghawar. The field’s highest production was 5.7 MMbopd in 1981. Water cut (ratio of water to total liquid production) in the field was about 35 percent in 2003. Gas production was about eight billion cubic feet per day, out of which two billion was associated gas and six billion non-associated gas.
The International Energy Agency has placed Ghawar’s ultimate oil reserves at 140 billion barrels, including 66 billion barrels already produced and 74 billion barrels remaining oil.
How accurate these estimates are remains to be seen – but to put these figures in context, consider that the proven U.S. oil reserves currently stand at about 22.3 billion barrels.
It is apt to end this essay with a note on Steineke, a Stanford graduate and Aramco’s chief geologist, who contributed so much for the early oil discoveries in Saudi Arabia. He died in 1952, one year after Ghawar came onstream.