KUWAIT - Geological Profile.

Kuwait is one of the world's prolific oil provinces, despite its small size, with an area of just over 18,000 sq km. Most of its oil reserves so far lie in relatively shallow formations (Fms) found before the 1970s.

Compared to its neighbours, Kuwait is still not rich in natural gas other than the one associated with oil. Most of its non-associated gas discoveries have been of poor quality. But like Iraq (see survey of Iraq in APS Review 17-20), there could be a good potential for oil and gas in deep formations yet to be explored.

Petroleum discoveries in Kuwait have been concentrated in the eastern portion of the onshore area. Excluding Kuwait's share of the Khafji and Hout fields which are offshore and part of the Divided Zone with Saudi Arabia, all of Kuwait's 11 producing oilfields are onshore and some of them are connected. The big ones, like Magwa and Ahmadi, are part of the Burgan super-giant which was first discovered in 1938. Little exploration has been carried out in western Kuwait, although the most interesting discoveries were made there in the 1980s, and in the offshore. There has been no exploration in Kuwait's easternmost waters which are subject to territorial dispute with Iran.

The fields in Kuwait are generally oriented north-south, as in the case of Rumaila on the Iraqi side of the border. They follow trends seen in Iraq and in Saudi Arabia. The pattern, well developed in the Arabian Peninsula, is related to deep-seated salt tectonics associated with basement faulting. Despite the great thickness of sediment overlying the salt, the deeper structures have had expression up to the surface and have produced broad, gently dipping folds in the younger strata. The presence of paleostructures, i.e. structures growing during deposition, may have been responsible for the excellent primary porosity seen in many of the reservoirs. So, as in much of the eastern part of the Arabian Peninsula, the juxtaposition of adequate source rocks, optimal geothermal conditions, and satisfactory migration paths have resulted in the concentration of large volumes of oil in the available closed structures.

Oil in Kuwait lies mainly in the Middle and Lower Cretaceous Burgan sand. Big quantities also occur in the Upper Cretaceous Mauddud limestone and Wara sandstone Fms. Below the Burgan, the Ratawi limestone and the Minagish oolitic limestones act as major reservoirs. But Minagish oolites contain high-sulphur hydrocarbons with toxic hydrogen sulphide. To the south, in the Divided Zone and in a similar tectonic setting, the Eocene Umm Er Radhuma and Dammam limestones are also productive.

The Ghar sandstone, a lateral equivalent of the Asmari limestone, is the reservoir in Kuwait's most northerly field as it is in several Iraqi fields to the north. Called Ratqa, it is a southern extension of Iraq's Rumaila super-giant. When it was found in 1978, it was thought to be a separate reservoir in a shallower Oligo-Miocene Fm. Ghar was found in the first half of the 1980s, when Iraq was at war with Iran. Below Ghar at Ratqa is an Early Cretaceous Fm, explored on the Iraqi side and known as Yamamah. It contains oil of 37-40 deg. API with low sulphur. It could be a giant. On the Iraqi side the Fm is more than 4,000 metres deep. Before the war to liberate Kuwait from Saddam's Iraq in early 1991, Rumaila, 80 km long, straddled the border and extended 3.6 km into Kuwait.

(Ratqa was one of the causes of conflict with Iraq in 1990. Much of its oil used to be pumped by Kuwait during the Iran-Iraq war. Just as a pump at the edge of a lake can pull water from an entire basin, Kuwait's wells there could in theory bring up oil from the Rumaila pool. During the weeks that preceded Iraq's invasion of Kuwait in August 1990, Baghdad had accused Kuwait of stealing its oil and had put the value of oil taken in the 1980s at "billions of dollars" - see background in Vol. 56, No. 21).

In 1984, a field was discovered at Abdali, on the border with Iraq to the east of Ratqa. But the oil, from a Miocene Fm, is heavy with a very high sulphur content.