Ghawar oil field, Saudi Arabia

 American Assoc. Petroleum GeologistsLocation of the Ghawar oil field. Source: American Assoc. Petroleum Geologists

Ghawar is by far the largest and most productive oil field in the world. It is located in the eastern part of the Kingdom of Saudi Arabia in a region known as the Empty Quarter desert.

 

It is about 200 east from the capital Riyadh and about 100 km WSW from the city of Dhahran. The field was discovered in 1948 by the Arabian American Oil Company (now Saudi Aramco), the nationalized Saudi oil company. The northern portion of Ghawar lies about 90 km west of the Arabian Gulf. From its northern extremity, the field extends southward some 230 km as essentially one long continuous anticline, about 40 km across at its widest point.

Although Ghawar is a single oil field, it is divided into six areas: Fazran, Ain Dar, Shedgum, Uthmaniyah, Haradh and Hawiyah. Geologically, the field is categorized as a fairly simple underground structure with a complete closure, a typical Middle East reservoir of porous limestone and dolomite. The oil comes almost entirely from a producing zone known as Arab D, about 2,100 meters below the surface.

Currently, the estimated proven reserves of Ghawar are about 70 billion barrels Arabian Light crude oil (33° API). Commercial production from Ghawar began in 1951 and reached a peak of 5.7 million barrels per day in 1981. This was the highest sustained oil production rate achieved by any single oilfield in world history. Cumulative production from the field is about 55 billion barrels. Today, Ghawar remains the world’s most important oilfield with a daily production rate of 4.5 to 5 million barrels per day. This represents nearly 6 percent of global oil production, a remarkable number given Ghawar is one of thousands of identified oil fields worldwide.

Ghawar’s amazing oil production has been aided by water injection that was initiated in 1965. Estimated injection rates are in the range of seven million barrels of seawater per day. This has produced an effect known as “water cut,” which is the joint production of oil and water from a well. Ghawar’s water cut currently is about 30-35 percent.

Ghawar also produces about 2 billion cubic feet of associated gas per day, and it has the capacity to produce upwards of 5.2 billion cubic feet of non-associated gas from the deeper Paleozoic section, where it’s trapped in Permian, Permo-Carboniferous and Devonian reservoirs at depths between 10,000 and 14,000 feet. This deep gas is generated from Silurian shales, which are the main Paleozoic source rocks in the Middle East and North Africa.

There remains considerable debate about the future ability of Ghawar to sustain its current rate of oil production. In 1975 Exxon, Mobil, Chevron and Texaco estimated that the ultimate recovery from the field would be about 60 billion barrels. Saudi Aramco claims that it can recover another 125 billion barrels from Ghawar, due largely to improved recovery technologies. Most analysts agree that better technologies have boosted ultimate recovery, but are very skeptical of the company’s more optimistic claims.

The debate about Ghawar’s future is largely speculative because the Saudi government closely guards field performance information and field-level production details. Much of the information about Ghawar is historical (pre-nationalization), comes from technical publications of unknown accuracy, or is anecdotal in nature.

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