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Progressing Mariner

Written by  Elaine Maslin Friday, 01 September 2017 00:00

Offshore heavy lift installation work is complete, and hook-up and commissioning work has started on Statoil’s Mariner heavy oil field. Elaine Maslin reports on progress, including work optimizing the field’s 100+ wells scope.

Statoil’s 38,000-tonne topsides installed. Photos from Statoil/Jamie Baikie.

Over July, Statoil’s US$7 billion Mariner heavy oil development took a major step forward. After travelling across the world on five Dockwise heavy transport vessels, the Mariner A platform’s nine modules were installed on the Mariner A jacket using the Saipem 7000 crane vessel, about 150km east of Shetland on the UK Continental Shelf (UKCS).

The Safe Boreas flotel then moved alongside to support some 480 of the up to 750 staff that will be working on the 38,000-tonne platform hook up and commissioning project over the next year or so, leading up to first production in 2H 2018, with storage and offloading by the Mariner B floating storage unit.

Mariner has been a long time coming, says Vidar Nygadr Karlsen, completion manager, who has spent the past two years overseeing the facilities construction in South Korea.

“We say this is the awakening of the giant field,” adds Uno Holm Rognli, project director for Statoil.

Mariner was discovered in 1981 and had 18 wells drilled on it already when Statoil took over the Mariner license in 2007. Statoil drilled its first well on the field last year. But, the firm spent a lot of time maturing the development, Rognli says. New seismic, from 2012, played a key role in unlocking the field’s reserves, helping Statoil to map their location and extent. “That made it possible to see where the oil was for us to have a good plan to develop the field,” he says.

Installation work using the Saipem 7000. 

The nature of the sandy, heavy oil reservoir will mean Mariner A will, for many years to come, be an intense factory, with more than 100 wells planned, from a jackup rig, the Noble Lloyd Noble, and a platform-based rig, supported by a well completion and workover deck, on Mariner A.

It’s a learning process, Rognli says. One challenge is drilling through the sandy reservoir. Here, Statoil is refining setting depth and mud weights, in order to maintain formation integrity, and will also be looking at casing sizes and completions solutions, Rognli says.

All wells will have electric submersible pumps (ESPs). Here, Statoil will be applying learnings about the life of ESPs from the Peregrino heavy oil field offshore Brazil (Read: OE September, Heavy Opportunities).

The first wells will have gravel packs, but Statoil will be testing where it can emit their use. Similarly, inflow well control will be used on four of the first six wells, with two wells to be left without, so that Statoil is able to compare results. “It’s a balance. The more wells we drill the more information we get and then we can make better decisions,” Rognli says. “We can switch to autonomous inflow control devices if we believe they can get us more oil. But, we want some production history. We have time to change things and implement new technology.”

By the start of the heavy lift campaign, in early July, two wells had been completed and two partly drilled. Another well is expected to be completed before first oil. Statoil is using geosteering and deep resistivity tools, which can help the well path track the roof of the reservoir as close as possible. “That’s proven quite successful,” Rognli says.

Mariner will produce from two reservoirs, Maureen and Heimdal. Statoil is drilling Maureen first, with Heimdal coming after a year or so. On Heimdal, because less was known about the reservoir, the initial plan was to cover the field with a wells grid, accepting that some wells might miss, like in onshore drilling. “Since we got new seismic, we have a better understanding of the targets and we can do horizontal drilling,” Rognli adds. Water management will be another significant factor for Mariner, with water production and injection.

Another nearby project to Mariner, the Bressay heavy oil field, had been due to follow Mariner, but has since been parked. “Bressay [is] even more complicated and difficult than Mariner,” Rognli says, of why Statoil put the field on hold. Statoil wants to learn more about Mariner, which has taken on learnings from Grane, in Norway, and Peregrino, in Brazil, before tackling Bressay, he says. “We hope we can do something with Bressay, but we do not know,” he says. “We have to look at the concept. We are sort of starting from scratch.”

But, there could be more investment in Mariner yet. One of Statoil’s three planned exploration wells in the UKCS this year will be in the Mariner area. Statoil is also drilling an appraisal well on southeast Mariner, using the Noble Lloyd Noble jackup. This could help prove up further reserves and may result in more investment.

“The problem with heavy oil is that it is difficult to do a subsea tieback, it would probably have to be a wellhead platform and some sort of processing before being sent back [to Mariner|. We want to drill two wells to see what we have. The potential development of southeast Mariner depends on how much we find.”

Production from 3-5 wells is due to start on Mariner in 2H 2018, via the Mariner B floating storage unit, which is already on station. It will both export the oil via a shuttle tanker, but also import diluent, for use mobilizing the heavy Mariner oil.

Once on plateau, the field will produce 55,000 boe/d, with an aim to produce at least 250 MMboe of the 2 billion boe in place over its life time. That could be increased over the life time of the field as new technologies are developed.

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