A team of subsurface and facilities engineers have been working together to create a viable, small footprint solution for a string of sour fields in the UK’s Outer Moray Firth. Mike Cooper explains.
For almost 40 years the Outer Moray Firth has been one of the most prolific producing areas on the UK Continental Shelf. From the early giant fields at Piper, Tartan and Claymore, through the major Scott and Buzzard finds in the 1980s and 1990s to new developments at Ettrick, Athena, Rochelle and Balloch, the basin has yielded over 6 billion bbl of oil to date, with more to come in the years ahead.
Indeed the production profile shown in Figure 1, which does not include the impact of the Golden Eagle hub, on stream in November 2014, attests to both innovation and rejuvenation in this area, despite the tragedy that impacted this area in 1988 at Piper Alpha.
Figure 1 – Oil production in the Outer Moray Firth, UK North Sea.
Image fromMike Cooper. Data from DECC website.
There are two other important trends in the Outer Moray Firth basin, which are clear:
- The mature oilfields (including Claymore, Buchan, Tartan, Ivanhoe (abandoned), Balmoral and Piper hubs), which have been in production for over 30 years, are now contributing less than 30,000 b/d collectively. Without major new investment, much of the aging infrastructure is predicted to cease production in the coming decade.
- “New” oilfields (e.g. Buzzard) generally exhibit steep production declines within a few years of start-up and, once these are stacked on the underlying decline curve from older fields, the decline curve steepens.
This is a major issue for the new government and becomes of greater concern when commodity prices are low. Some older fields barely cover the costs of operation and at US$45-65/bbl many will be losing money.
Figure 2 – Eastern Outer Moray Firth area. Current infrastructure map. Image from Mike Cooper.
The current infrastructure in the eastern part of the Outer Moray Firth is shown in Figure 2.
By contrast, Figure 3 illustrates this same area in 2025, based on predictions of natural declining production (courtesy of Wood Mackenzie January 2015 model). It is predicted that all but three fields are currently anticipated to be operational in 10 years’ time. Time will tell if this prediction is realized.
Figure 3 – Eastern Outer Moray Firth area. Forecast infrastructure map in 2025.
There is some hope for the area. Three companies – UK independents Parkmead Group, Faroe Petroleum and Atlantic Petroleum – are actively working to deliver the next phase of oil production in Outer Moray Firth region.
The Perth, Dolphin and Lowlander (PDL) oilfields, jointly containing about 80-90 MMbbl reserves were discovered in the 1980s, but have been overlooked for development for over 30 years. The oil is reservoired in Upper Jurassic sandstones in large stratigraphic traps in the 10,500-13,500ft subsurface depth range. Water depths are 130-140m.
One of the primary reasons these fields have not been developed before is that the existing platforms and floating production, storage and offloading (FPSO) developments in the area are not designed to handle the sour gas, or gas containing hydrogen sulfide (H2S) at these fields.
Parkmead, Faroe and Atlantic have been working on a design to handle these fluids, which would allow safe and efficient processing of the oil and gas and minimize the environmental footprint. It would also be the first dedicated floating facility that can handle sour fluids in the North Sea.
The current plan is to use a ship-shaped FPSO moored near the Perth oil field in block 15/21c and tieback the Dolphin (8km to the southeast) and Lowlander (16km north) oil fields to this facility.
In total, eight producing and four water injection wells need to be drilled to deliver the 80-90 MMbbl reserves. The FPSO will be designed for a 20-year field life, with capacity to produce up to 50,000 b/d. All the producing wells will be fitted with gas-lift equipment to maximize production rates and reserves recovery.
Key considerations on the design include all materials have to be H2S-resistant including the risers, in-field flowlines, tree lining and production tubulars. Processing onboard this newbuild vessel has been designed with an amine process with stabilized offshore loading to DP tankers and excess sweetened gas exported to nearby infrastructure. A two-stage separation train, is followed by a stripping column for removal of H2S and volatile mercaptans from the oil. Sweetened associated gas will be used as the stripping medium.
What’s more, it is envisioned that the facility would be able to handle other liquids in the broader PDL area, estimated to contain more than 1 billion bbl of oil in place, creating the potential for a significant hub development.
“The PDL project represents one of the largest undeveloped oil projects in the UK North Sea,” says Tom Cross, Parkmead’s executive chairman. “The engineered solution enables us to produce the oil safely, efficiently and with minimal environmental impact from three new fields. A collaborative effort to equalize the interests in these three oilfields and develop a new hub has been fundamental in unlocking this resource,” Cross continues.
“Older, existing oilfields where seawater has been pumped into the reservoirs for pressure support for decades have a tendency to become ‘sour’ underground over time. The PDL facilities will be able to handle such sour fluids in addition to those from the Perth, Dolphin and Lowlander oilfields and other currently stranded sour crude discoveries,” Cross says.
The project has also overcome another hurdle. Historically, misalignments in field ownership has contributed to delays in developing oilfields. PDL now has a common ownership, which means for the first time in decades there is the opportunity to focus on an optimal development plan for all three fields combined in one hub development.
To date, 13 wells have been drilled across the three PDL fields, and Parkmead believes they are adequately appraised to sanction an economic development in the near future.
The fields contain up to 12,000ppm H2S, contrasting with the 190,000ppm on the giant Kashagan project offshore Kazakhstan. Worldwide there are numerous examples of oil fields producing safely despite having sour gas concentrations an order of magnitude higher or more than we see at PDL.
A team of subsurface and facilities engineers have been working on behalf of the PDL partners to optimize the economic development of the three oilfields and it is expected the PDL facility would become one of the key strategic infrastructure resources in the Outer Moray Firth for decades to come.
PDL is one of the largest and most robust remaining conventional oil field projects in the UK North Sea. Collaboration and innovation have allowed the important resource in three fields to be unlocked through one facility with the smallest environmental footprint.
Mike Cooper has over 30 years’ experience in the oil and gas industry. Cooper has held senior subsurface roles with Lundin, Centrica, DEO Petroleum, Black Star Petroleum, EnQuest and Maersk. He is co-founder and CEO of Arenite Petroleum, a new company set up to explore conventional and hybrid UK plays onshore and offshore. Cooper was founder and former chairman of the annual Devex Conference and is a former director of the PESGB, and technical director at 1st Subsurface Oilfield Management. He holds an MSc in petroleum geochemistry from Newcastle University and a BSc (Hons) geological sciences from Leeds University.