For OE, 2015 is a milestone year – it’s our 40th anniversary. We share that milestone with one of the world’s most iconic oil fields – the UK North Sea Forties field. Elaine Maslin charts the field’s history and finds out what the future holds.
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Sea Quest’s discovery was celebrated with a cake, which took 700 hours to make. Photo from BP. |
Forties is no ordinary oil field. In fact, for some, Forties is an individual – a field with character, personality and presence. For Apache operations director Bob Davenport, “she’s a beaut” and, while she’s 40 years old, she sits as the third largest oil producer on the UK Continental Shelf, with plenty of life left in her.
Concluding his presentation on the 40-year-old field at the DEVEX conference in Aberdeen earlier this year, Jeff Towart, Apache’s North Sea region exploitation manager said, “In 10 years’ time, someone will be presenting ‘Forties hits 50,’ and it will still be going strong.”
A basin opener
Forties’ reputation comes not just from its sheer size. The central North Sea field was discovered at a time when many had about given up on the North Sea. “Back in the 1960s, gas had been found in the southern gas basin,” Towart says. “Then there was a push northwards [for oil]. But, by the end of the 1960s, the industry was getting a bit disheartened with some of the disappointing results up there.”
In fact, in 1969, renowned geologist Miles Bowen was quoted as saying all the worthwhile gas fields in the southern North Sea had been found, while the search for oil in the North was doomed for failure, Towart says. Bowen wasn’t alone in holding that view and even Sir Eric Drake, BP’s chairman and CEO, said in April 1970 “there won’t be oil there.”
Nevertheless, BP held out and in October 1970, the Sea Quest semisubmersible drilling rig discovered Forties, in the South Viking Graben, 110mi east of Aberdeen, in 350ft water depth, with some 4.2-5 billion bbl in place. “This was a huge boost to the UK at the time,” Towart says. “Forties (named after the sea area it sits in) and some fields discovered shortly after squarely put the North Sea on the map as a major oil province. Forties really kicked off the offshore North Sea oil industry.”
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Photo by Paul Thomson. |
1975 start-up
After a frenzy of construction activity, production started in September 1975, from Forties Alpha (initially known as Graythorp I) platform, flowing to shore in November – an occasion marked by Queen Elizabeth II. Forties Alpha was the first oil platform installed on the UK Continental Shelf. Brown & Root was the main contractor, and by the end of 1975, the first four Forties platforms were installed: Alpha, Bravo (which was known at the time as Graythorp II), Charlie and Delta, (which were known as Highland I and II, respectively). The Graythorps were built at Laing Offshore, near Hartlepool, and the Highlands at Highland Fabricators at Nigg Bay on the Cromarty Firth. In 1979, production peaked at 550,000 b/d, higher than initial predictions. In 1986, Forties Echo was installed, followed by the Unity riser platform in 1993.
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A BP Archive photo from Forties from the 1970s. Reproduced with permission from BP Archive |
Forties Alpha, Charlie and Delta are self-contained drilling, production and processing units, with Bravo no longer processing fluids, but directly exporting them to Charlie for processing. Echo, having no processing facilities, exports its production fluids for processing via the Alpha platform. Charlie acts as a gathering platform. Processed fluids are exported to Cruden Bay and onwards to Kinneil via the Forties Pipeline System.
When production started in 1975, it was predicted Forties would stop producing in the early 1990s. By 1990, that was moved forward to 2000. Projects like the Forties Artificial Lift Project in the early 1990s, with gas lift and electrical submersible pumps, helped extend the field’s life, and, as of 2002, Forties had produced about 2.5 billion boe, somewhere a little more than 50% of its reserves.
Then, BP decided to sell the field, its “crown jewels,” for US$683 million to Apache. At the time, Forties was producing 41,000 boe/d and the remaining reserves were estimated to be 144 MMboe, with field life expected to end in 2012.
A new start
What happened next was a huge success story. Apache has gone on to produce about 240 MMbo (120 MMbo from Apache drilled wells) from Forties and thinks there’s another 100 MMbo to be had, Davenport said, speaking at SPE Annual Technology Conference and Exhibition last year.
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Forties Alpha and the FASP facility. Photo from Apache. |
Investment
A huge piece around Apache’s success on Forties has been investment. Since 2003, Apache has spent some $5 billion on Forties’ infrastructure and drilling, bringing four drill strings back into use, as well as investing in everything from the cranes through to the export pumps and a new gas and power ring main around the field – until then each facility was powered locally – with four new gas-powered turbines installed (20 older units could then be removed), and issues that beset the export system were also resolved. All of which has helped increase production efficiency and lifting costs.
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Drilling on Forties in the 1970s. Photo from BP. |
The year after the field was scheduled to cease production, Apache installed a new platform, the Forties Alpha Satellite Platform (FASP), adding 18 new wells slots and increasing compression, power generation and processing capacity.
As a result, in 2012 through 2014, Forties ranked as the second highest producer in the North Sea, compared to 10th in 2003. And the investment continues.
For Towart, the key drivers to the success of the field has been adding new barrels through the drill bit and ensuring they get produced efficiently while replenishing the target inventory and continuing steady capital investment.
Drilling
“Often people characterize the success at Forties around the aggressive drilling program,” he says. “The drilling program has averaged about 13 wells per year over the last 10 years. Last year, we drilled 17 wells. We had five consecutive drill strings running in the field and that was a new record in Forties history.” Some 75% of current production is from Apache-drilled wells.
Apache has also broken flow rate records on the field. In 2009, Apache flowed the Charlie 6-3 well at an initial rate of 10,500 b/d, the highest initial rate from a Forties well since 1994. That record was broken again in 2011, with Charlie 4-3 reaching 12.567 b/d.
“What the drilling has allowed us to do is create a late-life production plateau of about 40-60,000 b/d,” Davenport says, adding that many of these wells have been sidetracks, but Apache has also invested in downhole surveillance.
This year Apache is drilling 14 wells, with 10 planned for next year. These will be drilled from the platforms and the Rowan Gorilla VII heavy-duty jackup rig drilling from the FASP.
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Beneath the surface on Forties.Photo from Apache. |
Production efficiency
“It’s not all been about drilling wells,” Towart continues. “There’s been a strategic focus on production efficiency from early on. In 2013, production efficiency was about 64% [around the current North Sea average]. That has been increased to more than 90%. In fact, in 2012-13, Apache ranked No. 1 for production efficiency in the North Sea, which is remarkable given that these are some of the oldest assets [in the basin]. That has really been done through huge brownfield investment from 2003-2009. To put it in perspective, if production capacity is 60,000 b/d and we increase efficiency from 65% to 90%, that’s like adding 15,000 b/d to production. That’s adding value.” The investment has also helped reduce lifting costs to 45% less than the average in the basin.
Replenishing the inventory
But, Towart says if some of Forties’ success can be characterized by aggressive drilling, really the field’s story is around the portfolio growth, over time. When Apache bought the field, there were 38 targets in the portfolio, he says. During the redevelopment, 153 wells have been drilled, including sidetracks, and there are still 63 in the portfolio, he says – the target inventory keeps growing.
Key to the target replenishment is continued investment in seismic, Towart says. The first 3D seismic was shot over the field in 1988 – after 60% of the oil reserves had been produced. Apache shot more in 2005, 2010 and then 2013, with the next 4D shoot planned for next year.
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A BP Archive photo from Forties from the 1970s. Reproduced with permission from BP Archive. |
Over the years, improvements in acquisition technology and processing and interpretation techniques, have helped build a clearer map of the field. “To make 4D successful we are continually trying to improve 4D processing and that’s really about noise levels and repeatability,” he says. The data had some 30-40% noise in 1998-2000. That’s now been attenuated and is down to around 7%, he says, through better repeatability and matching. The better data is having results at the drill bit. “We are finding success rates in the field have climbed from about 78% to about 90% in the last year,” Towart says, thanks to these improvements.
But, it also helps having a world-class reservoir, he says. Forties is a Late Paleocene-aged turbidite channel complex deposited in a proximal submarine fan location, with a high degree of complexity influencing the flow behavior but also providing traps of by-passed oil accumulations that remain unswept.
Nearfield development
Other ways Apache has been adding value is through near field development. The Maule field came onstream in 2010, Bacchus, the first subsea tieback to Forties, came on in 2012, Tonto in 2013 and the latest, Aviat, is due on stream in 2016.
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A BP Archive photo from Forties from the 1970s. Reproduced with permission from BP Archive. |
Aviat will be a bit different. It is a two-well, 23km tieback fuel gas supply project for Forties – and yet another project to maintain field-wide efficiency. Many North Sea facilities are finding, as they age and gas supplies deplete, they require diesel as a fuel supply. Having installed the ring main around the Forties platforms early in its operation of the field, Apache has been looking for a new source of gas, which Aviat will provide, providing up to 19 MMscf/d of fuel gas.
Culture
For Apache, the success at Forties isn’t just about technology or investment. For Projects Group Manager Mark Richardson, what sets Apache’s Forties business apart is the firm’s approach to leadership, culture and behavior: “Our ability and flexibility to understand the opportunities available is central to this culture. So, we encourage risk taking, not safety risk, but around commercial, contractual, technical, reservoir, subsurface and project opportunities, because where you take risk, there is often reward.”
Towart says: “It is about nimble decision-making and pushing the decision-making process down through the organization, focusing on the right projects, risk-taking, personal initiative, and a sense of urgency.”
A healthy future
Forties, a field that had been scheduled to cease production in 2013, is a prime example of big fields that get bigger. Drilling and investment in the field, a core and profitable asset for Apache, even in today’s tough oil price environment, continues.
In the right hands, “Forties has hit 40 and it still has a lot of value to be gained,” Towart says.
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