SAUDI ARABIA - The Ghawar Fields.

Discovered in 1948 by the then US-owned Aramco (Chevron, Texaco, Exxon & Mobil), Ghawar is by far the largest axis of fields in the world and is the main producer of Arab Light in Saudi Arabia. It is 250 km long and 15 km wide. It contains several fields, of which eight are major oil producers, and huge fields of natural gas in a Khuff reservoir deep beneath the oil formations. Ghawar's proven recoverable oil reserves exceed 70 bn barrels. Oil in place is over 300 bn barrels.

It was Exxon which found the first Ghawar structure at Ain Dar in 1948, having joined Aramco in 1947. It led to discovery and development of other fields by Exxon. The bulk of Ghawar's currently produced oil reserves occur in limestones of the Jurassic Arab A, B, C and D units, mostly at a depth of 6,920 feet, with substantial amounts in older Jurassic limestone members. Beneath them lie giant Khuff and pre-Khuff gas formations.

The main oil producing Ghawar fields are, from north to south: Ain Dar, Shedgum, Uthmaniyah, Farzan, Ghawar, Al Udayliyah, Hawiyah and Haradh. Their installed capacity is 5.3m b/d, of which most of the heavier oil production streams have been mothballed. It was said in early 1990, when total Saudi capacity was less than 8m b/d, these fields still had the potential to produce 4m b/d, as some of the wells were filled with diesel to keep them ready. In 1980, as Saudi Arabia's output totalled 9.9m b/d, Ghawar at times produced over 6.5m b/d; but the reserver was damaged as a result, and now some of the older fields like Ain Dar have begun to decline and need EOR facilities. Haradh, in the southern part of Ghawar, would also require extensive EOR facilities in the coming years. The main boost to Arabian Light capacity has come from the 520,000 b/d expansion at Hawiyah. A $2 bn, 1,440 MCF/d gas processing plant being built at Hawiyah, will be on stream in late 2001 as the 4th in the Master Gas System (MGS). Hawiyah is rich in natural gas and condensates. On July 21, 1994, the Hawiyah-200 exploratory well yielded 20.2 MCF/d of sweet gas and 3,286 b/d of condensates from an interval of 13,650-14,353 feet. The well was spudded in January 1994 and was the first in a series of deep tests to explore new gas reserves on the flanks of Ghawar. It encountered zones bearing extensive sour and sweet gas deposits in a Khuff formation at 12,500 feet.

Deeper drilling through the Jurassic beneath other Ghawar oil structures had already since the 1980s proved up large reserves of gas sometimes with condensate in Permian Khuff limestones and pre-Khuff sandstones. These deposits had been actively sought since industries and utilities in the Eastern Province, which depended on associated gas for power or feedstock, had been deprived since oil production was cut back and associated gas production was curtailed. Now Saudi Aramco is developing Khuff and pre-Khuff gas reserves beneath Ghawar. A 300,000 b/d GOSP expansion at Haradh was completed in late 1995. A second 300,000 b/d GOSP will raise the field's capacity to 600,000 b/d by 2003 with some of the heavy oil the Ghawar area to be shut in. A $2 bn, 1,400 MCF/d gas processing plant at Haradh, the 5th, will raise capacity of the MGS to almost 9,000 MCF/day by 2005.

At Uthmaniyah, a major gas processing plant with a capacity of 1.6 BCF/day has been expanded to 2,400 MCF/d. A 152 km underground gas pipeline, known as UBTG-3, has been built to link Uthmaniyah's gas plant to the plants of Juaymah and Berri. Two new GOSPs at Uthmaniyah were built in late 1992. The Ghawar fields are now producing well below capacity, with the output being Arabian Light. The other Ghawar fields producing this grade are Khurais, Harmaliya and Abu Hadriya.

Gas production capacity at Ghawar has been expanded steadily, meanwhile, thanks to Khuff reserves developed in the past 12 years. Gas production should raise close to planned processing capacity of 9,000 MCF/d by 2005, with a major part to involve non-associated gas.

With oil production costs at Ghawar being the lowest in Saudi Arabia, the average cost of producing associated gas at the well-head is 20 cents/m BTU. Costs up to local buyers' receiving end exceed 65 cents/m BTU, with the price of gas being supplied to Saudi-based industries having been raised from 50 cents to 75 cents/m BTU as from the beginning of 1998. The well-head cost of producing non-associated gas is higher than 20 cents/m BTU. But it compares favourably with production cost estimates for Qatar's North Field. Total costs of non-associated gas up to the buyers' receiving end are believed to average about 55 cents/m BTU.

Associated gas at Ghawar contains 51% methane, 18.5% ethane, 11.5% propane, 4.4% n-butane and isobutane, 1.6% pentane, 0.4% hexane, 0.2% heptane, 0.5% N2, 9.7% CO2, and 2.2% H2S. Its calorific value is 1,300 BTU per cubic foot, compared with 1,270 in Qatar's associated gas, 1,200 in Algeria, and 1,130-1,134 in Egypt. The non-associated gas is richer in methane but poorer in ethane and LPGs.