In 2008, we experienced a major incident in which injected oily water migrated from the reservoir to the sea floor. An oil sheen on the sea surface was observed close to the Tordis subsea field. The emergency response system was mobilised, and after surveillance of the seabed, a sink hole was discovered approximately 300 metres from the injection well. Oil-contaminated water was pouring from the hole. The migration of oily re-injected water to the surface had been caused by the fracture of overburden from the Utsira formation to the sea floor. The discharge was estimated to be at most 175 cubic metres of oil to the sea.

We have investigated the Tordis case, and the report identifies several serious matters related to planning and implementation of the injection well on Tordis. The company has proposed a number of measures to ensure that the identified impairments and faults are rectified. The Petroleum Safety Authority Norway (PSA) did not identify any matters beyond those described in StatoilHydro's investigation report.

In 2007 a similar case was reported at Visund. A pile of sediments was observed on the seabed beneath the Visund platform, which seemed to be linked to a drill cuttings injection well. The discharge was estimated to be between 5,000 - 7,000 cubic metres of drill cuttings to the seabed. There are several possible explanations for how this could happen - a shallow leakage, leakage along a casing, a formation fracture, opening of a possible fault or a combination of these. StatoilHydro is now working to identify the cause of this leakage.

It is of great importance that the experiences from Tordis and Visund are communicated internally in StatoilHydro and in the industry in general to ensure that storage in geological formations takes place in a safe and acceptable manner.

The injection of oil-contaminated produced water and injection of drill cuttings into geological formations are important technologies for oil companies to reduce the environmental impact from their operations. The injection of drill cuttings and produced water is an accepted technology according to international conventions.

Since the Tordis injection breakthrough passed through the Utsira formation - into which StatoilHydro is reinjecting carbon dioxide from the Sleipner field more than 300 kilometres to the south - questions have been raised about the reliability of the Utsira formation as a storage site for carbon dioxide. The Utsira formation at Tordis and Sleipner is part of the same geological formation, but the two fields are 300 kilometres apart. The Tordis field is located in a region where the Utsira formation displays very different rock qualities from those found at Sleipner. This means that fluids and gas do not migrate between the different regions within the Utsira formation. Carbon dioxide from Sleipner will eventually dissolve in the formation water and sink to the reservoir bottom long before it can reach the Tordis area. After carrying out several repeated seisimic, gravimetric and electromagnetic monitoring surveys over a 12-year period, most recently in the summer of 2008, we are confident that no leakage of carbon dioxide is either ongoing or expected from the Sleipner injection. Today the north-south extension of the Sleipner carbon dioxide plume is little more than three kilometres long.