Kashagan, Caspian Sea, Kazakhstan

Discovered in July 2000, Kashagan could prove to be the world’s fifth largest oilfield. It is owned by a group of partners led by Agip.

A US$300 million regional eco-seismic research study was conducted in the Kazakhstan sector of the Caspian Sea, providing 26,180km of 2D data, covering 110,000km².

The entire Caspian Sea is around 30m below sea level and while the mean water depth as a whole is 208m, this is considerably shallower to the north-east. The field, 75km SSE of Atyrau, lies in just 3.7m of water.

Temperatures can fall below -20°C in winter and a coating of ice, several metres thick, forms in this part of the Caspian Sea for many months of the year.

FLOATING PRODUCTION VESSEL

The drilling programme is being carried out by the Sunkar (which means 'falcon' in Kazakh) floating production vessel.

This converted swamp barge was re-designed and modified specifically for Caspian service, in a US$100 million engineering exercise, which included the installation of two 4m-high steel deflector tanks to protect the rig from the ice. The barge measures 85x53m and is 5.5m high - the largest of its type in the world. It weighs 6,000t.

In order to minimise supply operations, the platform design required storage-tank volumes that were as large as possible. The tanks include 19 ballast tanks (18,869m³), five drill water tanks (1,854m³), five fuel oil tanks (1,364m³), one pollution tank (516m³), four potable water tanks (513m³), one base oil tank for mud (385m³) and one brine tank (224m³).

SUPPORT FACILITIES

The platform can accommodate 96 people, although under typical conditions, there are usually only 80. Support facilities include a bacterial sewage unit, capable of handling 9.5m³ and two electrically driven Alfa Laval freshwater distillers, consisting of two units each capable of 33m³/day. Communication is maintained by radio and a satellite voice-and-data link, and there is a 19x19m helicopter deck. Power is provided by four 1,500kW power generators and one 860kW standby generator. Emergency power is available through the 420kW diesel-driven generator.

The rig barge sits on submerged limestone berms that stand less than a metre high. The berm is surrounded by 24 ice-resistant piles, each weighing 70t. They are 1.6m in diameter and 30m tall. These are used to break up ice sheets and reduce forces on the barge.

DISCOVERY WELL

The discovery well, Kashagan East, was a single vertical well, drilled to a total depth of 4,500m. The first stage of the well involved drilling a pilot hole of a starting diameter of 9 7/8in, to check for shallow gas. The main well commenced at a diameter of 26in (which increased to 1000m). The well plan envisaged drilling a 17 1/2in hole to 2310m, a 12 1/5in hole to 3,933m and a 5in hole to 4450m. The planned drilling time is 120 days (150 days with testing). Dresser Services won the integrated drilling contract. The drilling was carried out from a 47m-high drilling mast, rated at a 624t (1,375,000lbs) maximum hook load. It has a 9,144m (30,000ft) drilling capability.

Because of the environmental conditions, icebreaking supply boats are used. Most icebreakers work using the weight of the ship, coming down from above, to crack the ice, however this system will not work in shallower waters. These vessels - delivered in October last year - break ice in reverse, using specially designed propellers. Special tugs also had to be designed to work in waters under 4m deep. They were newly built in a Helsinki shipyard and arrived in the Caspian sea in September 2002.

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