Installations on the field have also produced oil and gas from Hod, about 13 kilometres further south. This small development was permanently shut down in 2013. Discovered in 1975, Valhall was the fourth commercial find made on the NCS. Amoco Norway Oil Company was the operator and responsible for drilling. Development of the field was approved in 1977, and production began in October 1982. Hod was discovered in 1974, but was so small that it remained non-commercial for many years. Development plans for this field were finally approved in 1988 and it came on stream in 1990.
Valhall produces from chalk formations deposited in the Late Cretaceous and known as Tor and Hod. The reservoir lies at a depth of 2 400-2 700 metres. The rock in the Tor formation is fine-grained and soft, with relatively large fractures which allow the oil and water to flow through more easily than in the Hod structure.
People who know Valhall well describe it as a very special field. The more it produces, the larger the remaining reserves appear to be. When the plan for development and operation (PDO) was originally submitted to the government in 1977, Valhall was estimated to contain 247 million barrels of recoverable oil. By 2014, it had yielded almost a billion barrels of oil equivalent and the vision is to recover a further 500 000. Both technological advances and enhanced efficiency will be needed to release the field’s full potential.
Little Hod was discovered in 1974 and began production on 30 September 1990. It was remotely operated from the main Valhall field.The field was originally developed in 1982 with a quarters platform (Valhall QP), a drilling platform (Valhall DP) and the process and compression platform (Valhall PCP).
A wellhead platform (Valhall WP) was installed in 1996 to provide an additional 19 well slots. Approval for a new PDO was obtained in 2000, and the injection platform (Valhall IP) was installed in the summer of 2003 to carry water injection equipment.
In connection with this approval, the licence expiry date was extended from 2011 to 2028. And yet another PDO secured a green light in 2001. A flank development embracing two wellhead platforms (flank south and flank north) was brought on stream in 2003 from the first of these units. The northern flank followed in 2004.
Yet another application to extend the licence was submitted to the government in 2006. The operator – by now BP – envisaged that the field would stay on stream for many years to come.
A new PDO entitled “extended producing life for Valhall” accompanied this request. The extension sought would mean keeping the licence until 2049.
The seabed over the Valhall field had subsided so much that the QP no longer met the applicable safety standards. A new process and hotel (PH) platform was planned to replace both the QP and the existing PCP. BP had also developed plans to meet the energy requirements of the field by transmitting electricity from shore, with the new PH facility as the reception point.
This platform was installed in 2012, making Valhall the first field on the NCS to be converted from locally generated diesel-generated electricity to power from shore.