In late 2018 a thirty-year adventure will begin 250 kilometres off Scotland’s north-east coast. That’s when the first oil tanker will leave the Mariner field, bound for the world’s energy markets. It’s been a long journey. Mariner is a sleeping giant, discovered more than thirty years ago.
But because of the oil’s extremely high viscosity, previous operators were not able to extract it. In 2007, we acquired the operatorship, and with the experience gained from working with other heavy oil fields, we managed to solve the challenges. The Mariner project will be one of Statoil’s most innovative developments ever.
Discovered in 1981 on the East Shetland Platform, approximately 150 kilometres east of the Shetland Islands, the Mariner field is a daunting prospect for oil and gas producers. Mariner is a heavy oil field characterised by dense, viscous oil.
In December 2012, Statoil and its partners decided to take on the challenge and made the investment decision for the Mariner project, which entails a gross investment of more than GBP 4.5 billion. This was the largest capital commitment to the UK Continental Shelf (UKCS) in more than a decade.
The concept chosen includes a production, drilling and quarters (PDQ) platform based on a steel jacket, Mariner A, with a floating storage unit (FSU), Mariner B. Drilling will be carried out from the Mariner A drilling rig, with a jack-up rig assisting for the first 4 years.
The Mariner oil field consists of two shallow reservoir sections: the deeper, Maureen formation at 1492 meters and the shallower Heimdal reservoir at 1227 meters. The oil is heavy with API gravities of 14.2 and 12.1 and viscosities at reservoir conditions of 67 cP and 508 cP, respectively for Maureen and Heimdal.
The development of the Mariner field will contribute more than 250 mmbbls reserves with average plateau production of around 55,000 barrels per day. The field will provide a long term cash-flow over 30 years. Production is expected to commence in 2018.
Statoil at the drawing board to save costs on Bressay
The Norwegian State-owned company Statoil and its partner, the Royal Dutch Shell (Shell), are considering all options in order to reduce costs for the development of the heavy crude oil offshore project, Bressay, in the UK North Sea.
In November 2013, while Statoil and Shell were expected to make the final investment decision, they in fact stepped back from that phase in the light of the first experiences acquired by the junior company Xcite Energy Resources Limited (Xcite or XER) from the similar field Bentley only eight kilometers away from Bressay.
Located 160 kilometers from the Shetland Islands, these heavy crude oil fields are concentrated together with Statoil Marinerand Enquest Kraken in the middle of the North Sea along the boarder with the Norwegian territorial waters.
In Bressay,Statoil and Shell are sharing the working interests in such a way:
– Statoil 81.625% is the operator
– Shell 18.375%
Discovered in 1976 for Bressay and in 1977 for Bentley, these fields were left undeveloped because of the challenging conditions of these 10 to 12 degree API heavy crude oil fields and associated sour gas.
Among these heavy crude oil projects of this area of the North Sea, Bressay is recognized as one of the most challenging for which Statoil and Shell mobilized all the lost advanced technologies.
As a result, when Statoil and Shell decided to stop Bressay development on its first concept, the project was estimated to cost between $6 and $7 billion capital expenditure.
Statoil and Shell to phase up Bressay development
With Mariner and Bressay, Statoil would have originated the largest projects in the UK North Sea.
But the first solutions tested by Xcite on the neighboring Bentley fields motivated Statoil and Shell to rethink their concept for Bressay.
With 257 millions barrels of recoverable crude oil (2P), Bentley is very similar to Bressay estimated to hold between 200 and 300 million barrels of recoverable reserves of crude oil.
Because of the nature of heavy crude oil in these fields, the production process developed by the companies is rather complex in order to optimize the recovery rate of these fields.
Typically these projects will require:
– Chemicals and diluents injection
– Risers and flowlines heating
– Oil and gas separation
– Water treatment
The accumulation of all these processes have a direct impact on the weight of the topsides and the definition of the structure to support them.
In Bressay, Statoil was considering a single large platform, similar to Mariner, while in BentleyXcite is combining a Sevan-type floating storage and offloading (FSO) vessel together with an Arup steel frame platform for production.
These differences in the concept are mostly related to the different methods of extracting the crude oil at the down hole.
In addition, the designed selected by Xcite provides all the flexibility to develop the field in phases, whereas the FSO remains all along the full development while the production unit can be adapted or even replaced at any time to the production goals and constraints.
With this new concept and costs revised downward, Statoil and Shell are expecting to sanction the Bressay phase-1 project in UK North Sea by 2016.
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Tags: 10 to 12 degree API heavy crude oil fields and associated sour gas, Arup steel frame platform for production, Bressay phase-1 project, Bressay platform, capital expenditure, Chemicals and diluents injection, Demulsifier, field Bentley and Bressay field, Final Investment Decision, FSO vessel, heavy crude oil fields, heavy crude oil offshore project Bressay in the UK North Sea, junior company Xcite Energy Resources Limited or XER, Norwegian State-owned company Statoil, Norwegian territorial waters, Oil and gas separation, recoverable crude oil (2P), recoverable reserves of crude oil, Risers and flowlines heating, Royal-Dutch Shell (Shell), Sevan-type floating storage and offloading (FSO) vessel in Bentley, Shetland Islands, Statoil Mariner and Enquest Kraken, topsides, water treatment
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