Sulphide stress corrosion is the direct cause of the gas leaks at the Kashagan field, according to North Caspian Operating Company B.V. (NCOC), the Kashagan field operator.
Replacing the pipelines at the oilfield, which lies in the Caspian Sea off western Kazakhstan, will cost between US$ 1.6 billion and US$ 3.6 billion, says the Kazakh Energy.
The multinational consortium developing Kashagan has identified stress cracking due to sulphur-laden gases as "the root cause of the pipeline issues" at the oilfield.
The final cost of the replacement will depend mainly on the resistance to corrosion of the pipes used in laying the new pipelines, the energy ministry said in the document sent to the Kazakh parliament.
The field's oil is 4200 m below the seabed at very high pressure, and associated gas reaching the surface is mixed with some of the highest concentrations of toxic, metal-eating hydrogen sulphide (H2S) ever encountered.
Edited from various sources by Elizabeth Corner