Testing was conducted on a single well in 1990-93 to investigate the potential and assess the risk of a large-scale injection project. This trial provided positive signals.
A new platform with 15 injection wells and nine slots for production wells was therefore proposed in 1997. Experience with this installation would provide the basis for later development of the flanks.
Uncertainty over the proportion of oil in place which could be extracted meant that the profitability of the project was fairly questionable, and a dialogue had to be conducted with the authorities over the financial terms.
These negotiations took time, but a tax package offered by the government in the spring of 2000 involved scrapping royalty with retroactive effect if the licence submitted a plan for development and operation (PDO) before the summer holiday.
The background for this offer was that the partnership had applied in December 1999 for royalty to be dropped and for the licence term to be extended by almost 20 years.
Given the big drop in oil prices at the end of the 1990s, which generated widespread pessimism in the industry, the government was keen to encourage increased activity as a means of providing new work for Norwegian industry.
A PDO for construction and installation of an injection platform was submitted ahead of the deadline and finally approved in November 2000.
The tight schedule meant that the cost estimates were inadequate or insufficiently prepared, and needed further work. Nor had all technical and structural aspects been fully developed.
The contract to design and build the platform was awarded to Aker in competition with Heerema, with Aker Verdal responsible for fabricating the steel jacket.
However, certain aspects of Aker’s jacket design were criticised by a number of experienced specialists. That related particularly to the question of whether the piling system would function, but Aker’s engineers gave assurances that such a solution had been used earlier and with good results.
The general view among personnel out on the field was that nothing was easy on Valhall, and this again proved to be the case. Problems with piling to the seabed meant that installation of the topsides was delayed for a whole year.
Aker Stord built the platform topsides, which had to sit at the yard while the experts worked out a solution to the piling problem.
But the waiting time proved a blessing in disguise, since it was used for a new review of the technical facilities. Alarming faults were found in the ultra-modern drilling rig, which the project team was now able to correct.
The topsides were installed in the summer of 2003, but not all the errors had been fixed and operation was further delayed. Initial water injection began on 24 January 2004, more than a year behind the original schedule.
Total investment in the platform ended up at NOK 7.2 billion, NOK 2.8 billion above the original estimate. Piling work alone cost NOK 1 billion.
An advanced life-of-field seismic (LoFS) system was installed on the field in 2003 (see separate article). This was intended to measure and monitor early progress with waterflooding, so that injection improvements could be made on the basis of experience.
The platform stands in 73 metres of water and is supported by a steel jacket. Of its 24 slots, 15 are allocated for water injection wells.
Weighing 10 000 tonnes excluding payload, the topsides measure 49 by 37 metres and are 22 metres high from the base of the cellar deck to the top of the derrick substructure.
The total height from the sea surface to the top of the derrick is about 105 metres. In addition, the cantilevered substructure allows the derrick to be moved over the neighbouring wellhead platform (WP) installed in 1996 in order to drill wells from there.
The injection platform has its own power plant, intended to generate sufficient electricity to drive the drilling equipment and the pumps for injecting water into the reservoir.
Daily capacity for water injection is 210 000 barrels (1.32 million litres). In addition, 140 000 barrels of produced water, which accompanies the oil up from the reservoir, can be processed every day.
Full tanks and fuel in the equipment add about 3 000 tonnes to the load.
The largest and most important components on the platform are:
Tag number Description
99-BA-8010 DERRICK STRUCTURE
60-XM-8000A MAIN GAS TURBINE GENERATOR PACKAGE A
60-XM-8000B MAIN GAS TURBINE GENERATOR PACKAGE B
90-MA-8000 PLATFORM CRANE A SWL = 60 T
90-MA-8010 PEDESTALE FOR 60T CRANE
60-XN-8020 EMERGENCY GENERATOR PACKAGE
09-BD-8010 21 1/4″ BOP STACK
90-MA-8020 PLATFORM AND JIB FOR 15T CRANE
84-XX-8030 MINOX DEAERATION UNIT
18-XX-8001 WATER INJECTION PUMP PACKAGE 63000 BWPD
18-XX-8002 WATER INJECTION PUMP PACKAGE 63000 BWPD
18-XX-8003 WATER INJECTION PUMP PACKAGE 63000 BWPD
18-XX-8004 WATER INJECTION PUMP PACKAGE 31000 BWPD
07-PB-8100A HP MUD PUMP A
07-PB-8100B HP MUD PUMP B
Tjetland, G, Kristensen, T G, and Buer, K (all BP): “Reservoir Management Aspects of Early Waterflood Response after 25 Years of Depletion in the Valhall Field”, IPTC 11276, presented at the International Petroleum Technology Conference 2007, Dubai, UAE 4-6 December 2007.
BP Amoco Valhall “Water Injection Project Plan for Development and Operation” (June 2000).