The Forties story began in 1964 when, under the new UK Continental Shelf Act, British Petroleum (BP) was awarded U.K. North Sea exploration licence number 001. In 1965, natural gas was discovered in the Southern North Sea by BP’s jack-up rig, Sea Gem. The search for hydrocarbons in U.K. seas had begun and soon the U.K. economy would change forever.
In October 1970, BP’s semi-submersible drilling rig, Sea Quest, hit commercial oil in Forties Field, situated in block 21/10 of the U.K. North Sea. The discovery, 110 miles east of Aberdeen, contained an estimated 1.8 billion barrels of oil and put the U.K. North Sea on the map as a massive source of energy and revenue.
Four fixed production platforms would be needed for the area which covered 91 square kilometers. Construction of the platforms themselves proved challenging, requiring extensive research and development as well as suitable construction sites - flat areas adjacent to deep water with a pool of nearby labour, all within 200 miles of the Forties Field.
Graythorp I and II (later known as Forties Alpha and Bravo) were constructed by Laing Offshore at a disused ship repair yard at Graythorp near Hartlepool, and Highland I and II (Charlie and Delta) by Highland Fabricators (HiFab) at Nigg Bay, on the Cromarty Firth.
For the next six months, the roar of heavy plant resonated through Nigg Bay as 16 earthmoving machines ate their way through 1.5 million cubic yards of sand dune, carving out a floor for the 160 acre yard and dry dock. Meanwhile, raw materials flooded in, piles were driven in to hold back the sea and a quay was constructed. Over at Graythorp, the operation was equally impressive.
As work continued on the platforms, pipeline construction began. A 107 mile underwater section would link the platforms to Cruden Bay pumping station. From there, a 130 mile land section would run to BP’s Grangemouth refinery near Edinburgh.
The 32 inch diameter pipeline would take a month to fill with oil. Once the oil arrived at the refinery at Grangemouth, it would need to be ‘stabilised’ to separate gas and ‘scrubbed’ to remove any odours. The stabilised crude oil would then be passed to either BP’s refinery at Grangemouth or to a new Tank Farm built at Dalmeny. Here, seven 60 feet high tanks could store 3.8 million barrels of crude oil, while another three stored ballast water.
In 1974, the Alpha and Charlie jackets were positioned offshore, with Bravo and Delta following in 1975. Nothing quite like them had been built before; the job pushed steel technology to its very limits while ensuring long-term capability. From below 300 feet of sea, stood the huge jacket legs that had dominated their respective construction yards for so long. From the air, the community at Forties now resembled something similar to a small village and the field was no longer the lonely spot it once was.
In September 1975, the first oil from the Forties Field travelled along the Forties Pipeline System to shore at Cruden Bay. The Forties field project was proving to be a great success, and on 3rd November 1975, it was inaugurated by HRH Queen Elizabeth II. BP Chairman, Sir Eric Drake, looked on as she pushed a gold-plated button at BP’s control centre in Dyce, Aberdeen. Production had officially begun - at a promising rate of 10,000 barrels per day.
Once all four drilling platforms were operational, the 130-well system had a production capacity of around 500,000 barrels per day. After the installation of the Forties water injection system in 1976, it quickly achieved a design injection capacity of 450,000 barrels of water per day. By 1979, oil production from the Forties field peaked had at 500,000 barrels per day.
In May 1982, Forties had produced its billionth barrel of oil.
10 years after the installation of the original four platforms, a fifth platform was required for the southeast area of the Forties Field. In 1986, Echo was added, connected to Alpha via 12 inch and 6 inch pipelines. Echo was originally designed and installed as an unmanned platform, relying on Forties Alpha for its control facilities, power supply and processing capability. However, it has been manned more often than not.
Thanks to technological advances, today a well can operate with over 90 percent of the produced fluid being water. During the early years, this wasn’t an issue as the volume of produced water with the oil was relatively low, but by the late 80s, it was increasing – a concern at the time because if the water percentage crept up to 60 percent, the well would die. Artificial lift was necessary for the well to continue flowing, so construction and commissioning of the Forties Artificial Lift Project (FALP) commenced in 1989, with first gas introduced to Forties Alpha and Forties Delta at the end of 1991.
The installation of gas lift facilities simultaneously on all four platforms was a huge undertaking, requiring careful planning to synchronise onshore and offshore activity. Drilling crews performed workovers on 47 production wells on Alpha, Bravo, Charlie and Delta to convert them for gas lift service. This involved replacing the casing down to 670 metres to allow the wells to contain high-pressure gas. On Echo, electric submersible pumps were installed directly in the well, as no processed gas was available on the platform.
The Forties Field was far exceeding original expectations, and in May 1989 it reached another historic milestone: its 2 billionth barrel of oil.
In 1991, an investment of £1 billion funded the replacement of the original offshore 32-inch pipeline, which had now become corroded. The new pipeline from Forties Charlie to Cruden Bay was 36 inch in diameter and increased capacity from 630,000 barrels per day to 900,000 barrels per day. The investment also paid for two extra onshore pumping stations, a supplementary oil stabilisation and processing train at Kinneil, an additional crude storage tank at Dalmeny and a further crude oil loading jetty at Hound Point.
In 1993, BP tied in the new Unity riser platform, which lies to the west of the other Forties platforms. Today, Forties Charlie and Unity still serve as the reception point for oil from other North Sea fields transported through the Forties Pipeline System.
It had originally been predicted in 1975, that production from Forties would have stopped by the early 90s. As the field and platforms aged, production continued to decline with oil production around 75,000 barrels per day in 1997 and falling to 66,000 barrels per day in 1999. It had been expected to be shut down for good in 2000.
However in 2003, when production had further declined to around 45,000 barrels per day, BP sold its 97 percent share of the iconic field to Apache for $683 million. This was a controversial move as the Forties Field was seen as a status symbol for the U.K. It was described by the media at the time as akin to ‘selling off the family silver.’
At the time of the acquisition 2003, the Forties Field had 45 remaining producing wells estimated to contain some 144 million barrels of oil equivalent, after recovery of around 2.4 billion barrels. Apache immediately set out on an ambitious programme for Forties, beginning with an intensive re-evaluation of the field, which revealed a further 800 million barrels of oil-in-place: significantly higher than previous estimates.
In 2004, Apache drilled 12 new wells and performed platform repairs and maintenance. By the end of the year, average daily production was back up to 61,680 barrels per day, compared with 40,950 barrels during the same period in 2003.
A combination of 4D reservoir monitoring and new 3D seismic surveys, including the imaging of areas beneath existing platforms helped Apache in the placement of new wells, while safe drilling and completion programmes increased production and recovery.
In 2005, a fresh 3D seismic survey of the field was completed. Apache was proving that it had the ability to reliably identify and target un-swept areas of the field and its mass investment was exceeding everyone’s expectations.
In 2006 and 2007, Apache had installed a new power-generation and gas ring main and completed the upgrades to the water-injection system and the Delta V control systems. Forties Charlie’s main import header, which connected the field to the export pipeline, was replaced, as was its infield pipeline to Forties Bravo.
$198 million had now been invested in new equipment and facilities upgrades for Forties since the acquisition 2003. Apache was, indisputably, transforming the Forties field.
In 2009, Offshore Group Newcastle (OGN) had completed a concept study for a simple wellhead tower at Delta - just as Apache was completing one for Alpha. By the end of 2009, the resolution was to integrate both studies into a functional specification for a new bridge-linked platform, FASP, which would be positioned next to Alpha. In 2010, a £400 million ($648 million) contract for the construction of the FASP was initiated and work began. Float out of the FASP carbon steel jacket was in September 2012 with final commissioning in August 2013.
On joining the ring main, FASP has provided an additional two turbine generators of power. It has a production capacity of 25,000 barrels per day and provides 18 new slots for drilling additional development wells to target the pockets of oil that were inaccessible from Forties Alpha. Together with Apache’s various other upgrades and improvements, it has extended the life expectancy of the Forties Field by 20 years.
2012 also saw first oil from the Bacchus Field. Bacchus lies around 6.5km North East of Forties Alpha, in Block 22/6s North and was discovered in July 2005 with well 22/6a-14. Oil from Bacchus travels to the Forties Alpha platform via a 6.7km subsea bundled pipeline.
By 2013, Apache had invested £2.8 billion ($4.3 billion) in the Forties Field since its acquisition. It had produced 190 million barrels of oil equivalent, and its average daily production stood at 60,000 barrels per day.
Following the success of Bacchus, the Aviat subsea field development will be the second subsea tie-back to Forties and aims to provide fuel gas to the field. Providing up to 19 million standard cubic feet per day of fuel gas, this valuable source of fuel will help sustain Forties production for 15 years or more, in line with latest production forecasts and development of future targets.
"Slowly, slowly, the Apache culture gets hold of you and then you just embrace it. It's a completely different way of working but in my view, much more enjoyable." - Brian Tadeo, HSSE manager.