Gullfaks Sør

Location and Geology

The Gullfaks Sør oil field is located in the northern part of the North Sea, specifically in blocks 34/10 and 33/12, near the main Gullfaks field. The water depth in this area ranges from 130 to 220 metres.

The field produces oil and gas from several geological formations, including the Middle Jurassic sandstone in the Brent Group, and the Lower Jurassic and Upper Triassic sandstone in the Statfjord Group and the Cook and Lunde Formations. The reservoirs are situated in several rotated fault blocks at depths of 2400-3400 metres, with the Statfjord formation being particularly complex due to its heavily segmented nature with many internal faults.

Discovery and Development

Gullfaks Sør was discovered in 1978, although it comprises several discoveries made in later years. The initial plan for development and operation (PDO) for Gullfaks Sør Phase I was approved in March 1996, with production starting in October 1998. Phase II was approved in June 1998, with production commencing in October 2001.

The field has been developed using a total of 13 subsea templates tied-back to the Gullfaks A and Gullfaks C facilities. Additional developments include the inclusion of the Gulltopp discovery in 2004, the Skinfaks discovery and Rimfaks IOR in 2005, and the redevelopment of the Gullfaks Sør Statfjord Formation with new subsea templates approved in 2012. The Gullfaks Rimfaksdalen project, which includes the Rutil and Opal deposits, was approved in 2015.

Production

Production from Gullfaks Sør began in 1998. The field initially produced oil and condensate, with associated gas being reinjected. In the second phase, gas production and export were initiated, with gas being processed on the Gullfaks C platform and exported through the Statpipe to the Kårstø terminal.

As of recent data, the Gullfaks Sør field has recovered 91.72% of its total recoverable reserves, with peak production achieved in 2017. Production is expected to continue until the field reaches its economic limit in 2032. The field currently accounts for approximately 3% of Norway's daily oil output.

Recovery Strategies

The recovery strategy for Gullfaks Sør involves various techniques to maximize oil and gas extraction. The Brent reservoir is mainly produced by pressure depletion after gas injection ceased in 2009. For other deposits, such as the Lunde Formation, production involves depletion as well as pressure support from gas injection. Gas lift is used for the Skinfaks deposit, while the Gullveig, Gulltopp, and Rutil deposits are produced by pressure depletion and partial aquifer drive. Since 2017, gas production has been enhanced by two subsea wet gas compressors tied-back to the Gullfaks C platform.

Ownership and Operation

The Gullfaks Sør field is owned by Equinor, OMV AG, and Petoro AS. Equinor, formerly Statoil, operates the field as part of the larger Gullfaks complex.

Infrastructure

The oil produced from Gullfaks Sør is transported to the Gullfaks A facility for processing, storage, and further transport by tankers. Rich gas is processed on the Gullfaks C platform and exported through the Statpipe to the Kårstø terminal. The field's subsea templates are remote-operated from the Gullfaks A and C platforms.

Future Prospects

Despite being on production decline, Gullfaks Sør still has significant remaining gas volumes. New wells are continuously drilled in the area using a licence-owned rig. There are ongoing efforts to improve oil recovery, including the use of horizontal and extended reach wells, new completion and sand control technologies, and water alternating gas (WAG) injection. A study aimed at achieving an additional 10% improved oil recovery (IOR) from the Statfjord formation within Gullfaks Sør is also underway, focusing on various development scenarios and addressing geological uncertainties.

Economic and Resource Estimates

The total reserves and recoverable resources in the Gullfaks Sør field include significant amounts of oil and gas. As of 2015, the in-place reserves were estimated at 37.62 million Sm³ of oil and 17.61 billion Sm³ of gas. The field's current predicted oil recovery factor is around 18.75% up to 2030, with efforts to increase this through improved recovery strategies.

In summary, the Gullfaks Sør oil field is a complex and significant production asset in the North Sea, operated by Equinor and involving multiple stakeholders. Its development and production involve advanced technologies and strategies to maximize hydrocarbon recovery.