Operator Phillips made the fateful discovery in 1969 in southern North Sea block 2/4. The Norwegian Continental Shelf had been open for exploration for only a few years, and this was the first commercial oil find.
The US oil company, now known as ConocoPhillips, was able to take the field into production using a modified jack-up rig in a record-breaking 18 months. The average time from first discovery to first oil is currently about 10 years and five years for smaller discoveries under fast-track developments.
The Greater Ekofisk Area, which comprises several fields, was originally expected to finish production before 2011. The Ekofisk field was estimated to recover only about 17-18% of its reserves. That has since been extended to more than 50% recovery rate and potentially 40 more years of production, thanks largely to improved oil recovery methods.
Pioneer in Water Injection
One of the greatest contributors to increasing petroleum output in the Ekofisk area has been the introduction of water injection into the fields during the 1980s. Phillips conducted a pilot water injection into the chalk reservoir as early as 1981. Prior to that water injection for pressure maintenance and as a mean for increased recovery had only been tried in sandstone reservoirs. Chalk posed the problem of lower permeability and being more fragile and hence could be potentially damaged by water injection.
“Some thought at the time it wasn’t possible to produce from such a chalk reservoir at all,” said Stig S. Kvendseth, Conoco Phillips’ spokesman in Norway. “When it comes to water injection it was normal in sandstone. But it hadn’t been done with chalk.”
After positive reactions from the pilot project, Phillips made an agreement with the authorities for a new water injection platform. The company began injecting in 1987, which resulted in increased production. By the late 1990s, the company was injecting at peak as much as 900,000 barrels per day into the reservoir. Today, it still injects more than 500,000 barrels per day of water.
Water injection also ended up helping the field with another problem, subsidence. The company found in late 1984 that the Ekofisk Complex platforms were sitting lower in the sea compared to when installed. The breakwater wall around the Ekofisk tank had sunk several metres since it was installed in 1973. The cause was compaction in the Ekofisk reservoir 3,000 metres below the seabed as a result of oil and gas production, which made the seabed subside.
In 1987 Phillips jacked the steel platforms at the Ekofisk Complex six metres up and installed extension pieces on the legs of the platforms and reinforced the Ekofisk tank with a protective wall in 1989. The subsidence continued, and in 1996 and 1998 two new platforms were installed to replace some of the old Ekofisk Complex platforms.
“Water injection had a positive effect,” said Kvendseth. “It increased pressure gradually in the reservoir and today we are controlling subsidence with water injection.”
The introduction of new drilling and well technology – including horizontal wells – in the 1990s was the second major method for improving recovery at the field. The new methods also enabled oil companies to target reserves in shorter and wider reservoirs from one location.
“Other methods of increased recovery are studied, but for the time being, water flooding is most effective,” said Kvendseth.
40 More Years
The Greater Ekofisk Area has generated NOK 1,804 billion (2010 NOK) in value creation from oil and gas and processing services since its first started 40 years ago. The license partners have invested NOK 594 billion into the field and recouped NOK 206 billion in net profits. NOK 902 billion has been paid in taxes and royalty to the Norwegian state.
Now ConocoPhillips, together with partners Total, Eni, Statoil and Petoro, are about to invest a further NOK 70 billion to extend the life of the field for several more decades. The group submitted a plan for development and operation of Ekofisk South and Eldfisk II – the two largest producing fields in the Greatest Ekofisk Area – that will increase recovery by more than 470 million barrels of oil equivalents by 2028.
“Ekofisk is the oldest field complex in operation on the Norwegian Continental Shelf,” said Ole Borten Moe, Norway’s minister of petroleum and energy, in June. “It has been in production for 40 years, and with this decision we pave the way for 40 new years.”
The Ekofisk South plans call for building a new wellhead platform with slots for 36 production wells and a seabed facility with eight water injection wells. The project is expected to lift the recovery rate from the Ekofisk field from 49.5% to 52% (25-35 million cubic metres). Production is set to start-up late in 2013.
The plans for Eldfisk II comprise a new integrated platform – equipped with 40 new wells for production and water injection – that will be connected to the existing Eldfisk Complex. The new platform will also enable continued use of the existing platforms on the Eldfisk and Embla fields and two new wells drilled from the existing 2/7 A platform. Together, this will raise recovery from Eldfisk from 22% to 28.5% (35-45 million standard cubic metres), with production starting in 2015.
“This is a gigantic industrial project that will give large value creation and employment effects,” said Moe. “This will have a large significance for the Norwegian supplier industry.”