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Volume 24, Number 6November/December 1973

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Oscar For An Oilfield

Ghawar, an underground structure 150 miles long, is the largest—and most productive—oil field in the world.

Written by Brainerd S. Bates
Photographed by S. M. Amin

An oilman's map of eastern Saudi Arabia pinpoints the location of gas-oil separator plants, pump stations, pipelines, storage tanks, a refinery, a marine terminal and the many other kinds of installations required for the processing and shipping of petroleum. Clearly indicated too are all the oil fields whose production is sent through that myriad assortment of fixtures. One field shown on the map stands out above all others because of its sheer dimensions. Ghawar is the largest known oil field, not only in Aramco's concession area, but in the world. If there is one thing that is more impressive than Ghawar's size, however, it is its productivity. Along about the time this issue reaches its readers the field will be producing on the order of five million barrels of oil a day. Large as this figure is, however, the experts say it is modest when stacked up against Ghawar's potential.

The northernmost portion of Ghawar field lies about 60 miles west of the Arabian Gulf port city of Dammam, which is a 20-minute drive north of Aramco's headquarters community of Dhahran. From its northern extremity Ghawar extends southward some 150 miles as essentially one long continuous anticline, about 25 miles across at its widest point. Geologically, the field is categorized as a fairly simple 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 7,000 feet, on the average, below the surface.

Long before 'Ain Dar Well 1, the field's discovery well, was spudded in in 1948, geologists had a pretty good idea of Ghawar's potential. Along the whole piece of territory they could see, by means of detailed survey mapping, what they called "surface expression" of dips to the east and west. Later, as small, portable "structure drilling" rigs probed the earth, it was confirmed that these dips followed a somewhat parallel course below the surface on either side. It took little ingenuity on their part for geologists to reason that if two opposite sides slope outward from each other there must be a rise in between them, and this rise might be an anticline containing oil.

These structure indications were so clearcut that it was possible to bypass on Ghawar the use of technically complex seismic means of oil exploration (Aramco World Magazine, Jan.-Feb. 1966; Nov.-Dec. 1972). Structure drilling told the geologists all they needed to know before they recommended going for broke with wildcats and then production drilling. Development/ delineation drilling is still the means in progress of exploring and fully defining the oil-bearing anticline that has long given Ghawar its preeminence.

Before it became clear that Ghawar was actually one big field, wildcat wells were drilled over a period of nearly nine years in widely separated areas along the recognized Ghawar structural trend. Wildcatting began with 'Ain Dar in the north, then moved to Haradh at the extreme southern end. Success at these two broadly removed locations led to "fill-in" wildcats at 'Uthmaniyah, Shedgum and Hawiyah. Ultimately, on February 21, 1957, Arab D oil was also discovered at Fazran, the most northerly protuberance of Ghawar. There are today some 300 producing wells altogether in these areas of the field.

The oil being produced carries up gas dissolved in it, which must be separated out in stages in big vessels called traps before the oil can be pumped any distance for processing or export. There are, so far, 25 of these gas-oil separator plants (GOSPs) distributed over Ghawar field, with more in various stages of construction. The jumbo of all these plants, functioning up in the northern section of the field, is Shedgum GOSP No. 1, whose three pairs of traps operating in parallel together have a daily rated throughput capacity of 750,000 barrels of oil, piped in from wells producing in a surrounding area nearly 60 miles square.

After the two initial stages of pressure reduction, first down to 175 pounds per square inch and then to 50 psi, have been carried out in GOSPs at Ghawar, the oil with some gas still in it arrives by pipeline at Abqaiq, where stabilizers in the industrial area remove the corrosive and poisonous hydrogen sulfide initially present in all of Aramco's inland crude, making that oil "sweet" and fit for transporting further through pipelines and aboard tankers.

Everyone concerned with production at Aramco is acutely aware that oil is a highly valuable natural resource which must be brought out of the ground with techniques that make it as certain as is economically possible that first-rate oil field practices are maintained (Aramco World Magazine, Nov.-Dec. 1965). Saudi Arabian oil happens to rise through wells to the surface under its own innate pressure, but after a field has been produced for a long time that fortuitous force tends to diminish. A great deal of Aramco's best engineering talent concentrates exclusively on ways to maintain pressure in its fields by induced means.

In Ghawar this is accomplished by means of water, augmented in the 'Ain Dar area by gas. There exists in underground aquifers within the structure, but above the Arab D producing reservoir, water with such a high mineral content that it is completely unfit for human or animal consumption, or for agriculture. Some of this water flows downward by gravity through injection wells connecting the aquifer directly with the reservoir. Additional nonpotable water is pumped to the surface from specially drilled water supply wells and then pumped down with considerable force into the producing reservoir. A properly designed system with optimum strategic placement of the injection wells will maintain the reservoir pressure somewhere near its original force. At the same time, the water introduced under pressure into the reservoir will "sweep" the oil in the direction of the production wells.

Everything connected with a pressure-maintenance program in a field the size of Ghawar must obviously be on a massive scale to be at all effective. For example, the field has a total of 94 injection wells and 32 water supply wells, and more are being drilled. The pipelines which carry the great volumes of water for injection purposes must not only be huge in diameter but must have walls able to withstand extremely high pressures. No pumps previously existed in the marketplace large enough to handle all the water used in the injection program at Ghawar, so Aramco had to go out and have such pumps specially designed and built. The results were 20,000-horsepower giants able to handle a half-million barrels of water a day at approximately 2,000-pounds-per-square-inch pressure.

The planning, construction and operation of oil-production and pressure-maintenance facilities in such fields as Ghawar represents a deliberate, coordinated effort to produce crude oil in Saudi Arabia at optimum conditions. It is common knowledge in informed circles that the volume of crude produced daily by Aramco's fields, including Ghawar, is very substantial. While the company's storage tank capacity is large, and growing, it would take very little time to overflow its tanks with current production. This is a problem that company oil planners do not expect to face. Large quantities of oil are being produced in and exported from Saudi Arabia these days because there is a demand for it. Ghawar field is pulling its weight to help meet the world's urgent—and increasing—requirements for energy.

Brainerd S. Bates is Aramco's chief writer on petroleum and a regular contributor to Aramco World.

This article appeared on pages 14-15 of the November/December 1973 print edition of Saudi Aramco World.


Check the Public Affairs Digital Image Archive for November/December 1973 images.