Kashagan Field - Geology

Geology

The Kashagan contract area covers an area of over 5,500 square kilometres (2,100 sq mi) andconsists of five separate fields, producing formations from the Precaspian Basin. These fields are Kashgan, Kalamkas A, Kashagan Southwest, Aktote and the Kairan.

Kashagan is a carbonate platform of Late Devonian to middle Carboniferous age. The "reef" is about 75 kilometres (47 mi) long and 35 kilometres (22 mi) across with a narrow neck joining two broader platforms (Kashagan East and Kashagan West). The top of the reservoir is about 4,500 metres (14,800 ft) below sea level and the oil column extends for over 1,000 metres (3,300 ft). The field is in very shallow water being 3 to 9 metres (9.8 to 30 ft) deep. The seal is middle Permian shale and late Permian salt. The reservoir consists of limestones with low porosities and permeabilities. The oil is a light oil with 45 API gravity with a high gas-oil ratio and hydrogen sulphide (H₂S) content of 19%. The field is heavily overpressured which presents a significant drilling challenge. The figures for oil in place range between 30 and 50 billion barrels (4.8 and 7.9 billion cubic metres) with a common publicly quoted figure of 38 billion barrels (6.0×10^9 m3). The recovery factor is relatively low (15-25%) due to reservoir complexity, with between 4 and 13 billion barrels (640 and 2,100 million cubic metres) being the estimated ultimate recoverable resource.