WP wellhead platform – a real success

History

Planning for a fourth installation on Valhall began in 1992. The original plan for development and operation (PDO) described further platforms as phases 2 and 3, but these were put on ice because of low oil prices and uncertain reserve estimates. By the early 1990s, however, new reservoir models had been constructed on the basis of information from the production wells drilled over the previous decade.

The initial proposal had involved a platform similar to the one installed on Hod, which stood some distance from the field centre and was unstaffed. But this was modified in the PDO submitted in 1994 to a structure standing close enough to the original facilities to be reached by a bridge.

Industry and energy minister Finn Kristensen appointed a committee in September 1993 which submitted a report on the competitive position of the Norwegian continental shelf (Norsok) the following February. In accordance with the recommendations in this document, Jens Stoltenberg – who had taken over as minister of industry and energy – appointed seven committees to come up with proposals for making Norwegian oil production more competitive.[REMOVE]Fotnote: Norsok, main report, 1995, 5.

The WP was built right in the middle of this “Norsok period”, when attention in the whole industry was turned towards improving competitiveness. Combined with Amoco’s contracting strategy and its new project management programme, this helped to reduce total development costs for the structure by NOK 600 million. That represented a cut of almost 30 per cent from the original estimate of NOK 2.1 billion. This project was in fact the only one during the period to meet the ambitious Norsok goals.[REMOVE]Fotnote: Ministry of Petroleum and Energy, Norwegian Official Reports (NOU) 1999: 11, Analyse av investeringsutviklingen på kontinentalsokkelen , 1999.

Heerema Tønsberg won the engineering, procurement, construction and installation (EPCI) job for the WP and the bridge linking it to the process and compression platform (PCP). Rather than issuing detailed specifications, Amoco followed up the Norsok proposals by establishing functional (performance) requirements which the structure had to meet. That in turn gave the contractor plenty of scope to adopt solutions which suited its own expertise and capacity, as well as allowing it to use its own preferred subcontractors.

Responsibility for hooking the new platform up to the PCP was allocated to a core team comprising personnel from Amoco and ABB Offshore Technology.

The module support frame (MSF) was lifted into position on the supporting steel jacket during the early morning of 20 April 1996, and the bridge was in place a few hours later. Hook-up work could then start. First oil flowed through the facility on 3 June – less than a year after construction began. That made this the fastest development project on the NCS until then.

One of the most important reasons for building and installing the WP was to help increase Valhall’s overall daily oil production from 40 000 to 125 000 barrels.

Two new export compressors were installed on the WP in 1998 in order to boost gas pressure so that supplies from Valhall could directly enter the Norpipe system to Emden in Germany. That avoided going through the Ekofisk facility, which incurred a high tariff, and was negotiated in connection with the planning and execution of the Ekofisk jack-up project. BP had a new 20-inch pipeline laid from Valhall, with a direct tie-in to the Ekofisk export pipeline a couple of hundred metres upstream from Norpipe.

The Valhall gas had a heating value (Wobbe index) close to the upper limit of the European standard for use with burners, while Ekofisk gas struggled to stay within the lower limit. Blending these two grades meant that the gas entering the pipeline to Emden was well adapted to the requirements of the European market.[REMOVE]Fotnote: Interview with Asbjørn Tansø.

Technical content

The four-leg steel jacket stands 90 metres high and weighs 2 400 tonnes, including the piles holding it place. Weighing a total of 2 000 tonnes, the topsides with modules measures roughly 28 x 22 metres and is nine metres tall from cellar deck to main deck. The vent pipes stand 11 metres high from the latter.

The WP provides 19 well slots, all there was space for. Every well was to be drilled horizontally – an entirely new technique at the time, particularly for the planned lengths. An innovative approach was also to be taken to boost output by fracturing the producing zones and filling the cracks with special sand to keep them open.

Plans called for seven wells to be drilled in the first year, but only three were brought on stream because of completion problems. Nevertheless, oil output reached the planned level since these initial wells turned out to yield twice the anticipated production.

Installing the WP allowed estimated recoverable reserves in Valhall to be increased by almost 80 million barrels of oil and more than four billion cubic metres of gas.[REMOVE]Fotnote: Rasen, Bjørn (2007): LF6A. Valhall at 25 … and it’s only the beginning , 110.

The process

The WP has the capacity to produce 40 000 barrels per day, with the whole unprocessed wellstream being transferred through pipes running over the bridge to the other platforms. Installation of two compressors in 1998 meant that gas processed on the PCP had to be returned to the WP for its pressure to be raised before being exported via the new link to Norpipe.