LAST month, BP launched a West of Shetland project of huge strategic importance to the UK economy.
The $4.8billion (£3billion) redevelopment of the Schiehallion and Loyal fields is a huge undertaking by the company and licence partners, and will ensure that the so-called Quad 204 assets remain viable at least to 2035.
A new production ship has been ordered and the project is gathering momentum.
The prize is huge – more than the nearly 400million or so barrels of oil produced thus far. Indeed, with an estimated 450-600million barrels remaining to be produced, Quad 204 may yet make the North Sea billion barrels league.
The last time BP faced a 400million barrels brownfield opportunity, the company examined the idea but then backed away. Instead, the Forties oil field was sold to Apache, which has been cashing in ever since.
Schiehallion was found in 2003 and the news was broken exclusively in the Press and Journal.
The field – alongside neighbour Loyal – was developed based on a purpose-designed and built floating production storage and offloading (FPSO) vessel hooked up to 29 wells grouped into four subsea clusters. Designed production was up to 142,000 barrels per day (bpd) and storage was 950,000 barrels.
Despite various problems with the FPSO and its process systems, and difficulties sustaining designed oil output levels due to higher-than-expected associated gas content, the development has unquestionably been a success since it was brought onstream on June 29, 1998.
As the years ticked past, it became clear that there was far more oil present than initially thought and BP began mulling redevelopment in 2006.
“We realised that the Schiehallion/Loyal fields were getting bigger,” said Mark Burchell, subsurface manager, Quad 204 Redevelopment Project.
“We drilled appraisal legs from some of the production wells into deeper reservoirs. We appraised another chunk of the field that was not on production at the time.
“So the resource base was growing beyond what the current vessel could deal with long term; we were beginning to see a future right into the 2030s.”
Mr Burchell described oil quality in the new reservoir sections as similar but possibly a little better than the crude produced to date. He said there was a little more gas and this meant a large gas compression capability would be required.
“We knew about the gassier bits of the field back in 2006 but couldn’t find a way of producing them because gas compression on the current vessel isn’t high enough.
“The new vessel will have much higher gas compression, much more gas handling capacity, so we can produce the gassier parts of the reservoir.”
Project general manager Graeme Stewart said the decision to redevelop based on a new ship had been driven by the need to exploit the extra reserves with additional topsides facilities that just weren’t on the original vessel.
A new ship built to modern design standards made sense if BP was to attempt to push the asset to 2035-plus.
The new 270m vessel will store more than 1million barrels. It will be about 40m longer than the existing unit, which means more space for the extra topsides plant needed.
The plan is to get oil output back to 130,000bpd. Gas compression will be 220million cu ft per day; the main water injection system will be capable of 380,000bpd, plus there is to be contingency of a further 190,000bpd, so taking water injection to 470,000bpd at peak.
“And the reason for that is that voidage; getting water into the ground is absolutely critical,” said Mr Burchell. “We know that from operating the current vessel. The ability to over-void the reservoir and catch up where there has not been proper voidage is crucial, which is why we have such a huge water injection capacity.”
In short, injecting water into the reservoirs, and lots of it, is key to getting another 20-25 years of production.
Mr Burchell said that seismic data had been very important in persuading BP of the value of redeveloping Quad 204.
“The key to unlocking this additional resource base has been the steady improvement in seismic. We shoot 4D (four-dimensional time lapse) surveys every two years out here and 4D has been one of the main tools in unlocking the extra resource,” he said.
But in terms of getting the extra oil out, what will it mean for drilling reservoirs that, in cross-section, resemble streaky bacon, the fatty strips being oil and the meaty parts rock.
Horizontal (including multi-lateral) drilling, so vital to unlocking Schiehallion resources the first time, will be used again. But the difference is that drilling and well construction technologies have advanced on 15 years ago.
Mr Burchell said: “Multilaterals have come a long way since the original wells were drilled, and so all proposed new wells will be screened for multilateral technologies. We’ve gone from cased and perforated to simple wire wrap screens. Now we’re into expandable sand control, gravel packs and variations on those themes.
“Of course, our ability to geo-steer the wells into complex reservoirs and pockets of hydrocarbons is now so much better because of seismic. One can now real-time navigate your way through the sub-surface.”
Turning to main contracts, the SURF bidding round, risers contract and outlook for drilling are covered in our lead story on page one.
However, there is much more to the project, not least building the ship and its process systems;. There is lso the mighty turret that will allow it to weathervane while safely producing oil. The designer/manufacturer is SBM.
“We’ve been working with SBM in Monaco for some time,” said Mr Burchell. “At around 24m turret diameter and about 10,000 tonnes total weight, it will be 10-20% larger than the turret fitted to our Skarv FPSO, and that’s a pretty big turret.”
The mooring system will be massive, too.
“Skarv, located out west of Norway, has a 16m significant wave design; we’re over 18m. The curve is logarithmic, so the forces on our vessel are way above those on Skarv. This vessel will have 20 mooring lines versus 15 for Skarv.”
The largest concentration of Quad 204 personnel is in Singapore and South Korea, with, of course, the beginnings of the ship, on which the development hinges, starting to take shape at Hyundai Heavy Industries. For its part, HHI has sub-contracted some topsides engineering design to KBR.
“We’ll probably build up to about 80 BP folk and about 200-300 KBR/HHI people in Singapore for another year, covering all topsides design, procurement, haz-ops (hazardous operations) and safety analysis,” said Mr Stewart.
“Around June/July 2012 that team will relocate to HHI at Ulsan in South Korea, where we presently have our hull team.
“The final pieces of the jigsaw are major items of topsides equipment. We have orders placed with Dresser Rand for gas turbines and Nanturbo for compressors, and so forth.
“These plus the turret will be delivered at various times out to HHI with sailaway scheduled for the final quarter of 2014. This means the new FPSO should be here (in UK waters) by early 2015 and, subject to the vagaries of the weather, we should be installing it offshore in mid-2015 and hooking up all the facilities.
Production will be suspended for some months to allow the change-out of vessels.
Newly revamped Schiehallion/Loyal first oil is expected in 2016.
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