Because of the Frigg reservoir’s special qualities, with high permeability, the production wells were concentrated in a small area of five square kilometres. The whole reservoir covered 115 square kilometres. Twenty-four wells were drilled with a maximum deviation of 45 degrees. Following a reassessment of the reservoir in 1990, CDP1 on the UK side was shut down and wells were drilled from DP2 to replace those on the abandoned platform. Drilling technology had advanced so far by then that wells could be driven horizontally over long distances.
DP2 stands on a eight-leg steel jacket piled to the seabed. The topsides with all equipment was 25 metres above the sea surface. Four modules were positioned one after another on the support frame. Each had two stories, with the lower for production and upper for drilling modules.
The wellheads were installed on the lower deck in module one, with 12 wells on either side of a firewall, while the derrick stood on the upper deck. Each wellhead was equipped with three safety valves – one downhole, one remotely operated master valve and one manually operated master valve.
Module 2 initially treated gas from the wellheads to remove water, condensate (light oil) and sand. However, it soon transpired that the reservoir produced little water or sand and this equipment was disconnected.
The volume of gas flowing from each well was controlled by a choke valve in module 3. From there, the gas (which still contained some condensate) flowed via a manifold to one of two 26-inch flowlines for onward transport to TCP2.
Workshops, transformers, fire pumps and an instrument room were located on the lower deck in module 4, with the control room and communication equipment on the top deck. The living quarters, with a helideck, were positioned on top of module 4. The quarters module was upgraded in 1980.
DP2 was shut down on 26 October 2004 together with the rest of the Frigg field.Elf’s corporate assembly formedDivision of resources clarified