Ultra-heavy oil fields development
Blocks 9/11a and 9/11b, North Sea, UK
97m to 112m
250 million barrels
Located in the northern North Sea, Statoil’s Mariner Area Development project calls for the development of Mariner and Mariner East ultra-heavy oil fields, with an estimated $7bn investment.
The project lies at water depths that range between 97m and 112m. It is located approximately 130km off the nearest British coast and 40km north-west from the UK / Norway international boundary.
The Mariner field is located in Block 9/11A, while the Mariner East is located in Block 9/11B on the UK Continental Shelf (UKCS). The latter is smaller in size and lies approximately 5km to the south-east.
Statoil will operate the Mariner Area Development with working interests of 65.11% in Block 9/11A and 92% in Block 9/11B. The remaining 8% equity in Block 9/11B is owned by ENI ULX, a subsidiary of ENI. JX Nippon Exploration and Production (UK) owns 28.89% in Block 9/11A, which the company acquired from ENI in December 2012, and Cairn Energy owns 6%.
Mariner Area Development project status
The development concept for the Mariner fields was revealed in September 2011. An environmental statement (ES) for the project was completed and submitted for approval to the UK Department of Energy and Climate Change (DECC) in May 2012. The final investment decision (FID) was announced in December 2012. The approval for the development of the oilfield was announced in February 2013.
Initial activities on the project started in 2016, upon receiving the clearance for development and operation. Offshore installation of the platform jacket was carried out in 2015 and the topside installation will be done in mid-2017. The Mariner field is expected to come on-stream in 2018. Mariner East will come on-stream two years later in 2020. The Mariner Area offshore project is expected to remain operational for 30 years.
Production from the North Sea fields
The now-defunct Union Oil Company of California (Unocal) had revealed the discovery of the Mariner field in 1981. All the four wells it drilled in the location produced heavy oil. The field was later re-valued by a multiwell appraisal programme in 1996-1997 by Texaco.
The Mariner and Mariner East oil fields are made up of two shallow reservoirs. The one in the Maureen Formation lies at depths ranging between 1,400m and 1,500m below sea level and contains oil with API gravity of 14.2.
The second reservoir is in the Heimdal Formation. It is situated at 1,200m below sea level and contains oil characterised by API gravity 12.1.
The project is expected to have a plateau production capacity of 55,000bbl of crude oil a day from 2018 to 2020. The combined oil and diluent, however, is expected to flow at the rate of 80,000bbls/day.
Drilling the ultra-heavy oil fields
The Mariner offshore field is scheduled to be produced with the help of 50 wells and 92 sidetracks, while fluids from the nearby Mariner East field will be tapped by four wells. The production drilling was started in 2016.
All the wells will be tied-back to a production, drilling and quarters (PDQ) unit secured on a fixed steel jacket platform. The PDQ unit, in turn, will be tied-back to floating storage and offloading unit (FSU).
All the wells at the Mariner field will be drilled by the PDQ platform and a jack-up drilling rig. The wells at Mariner East will be drilled by a semi-submersible drilling rig.
The platform will first separate gas and water from the produced oil. The stabilised oil will then be piped to the FSU vessel for storage. From there, it will be shipped to the shore through shuttle tankers.
The water will be re-injected into the reservoirs to maintain pressure. The gas will be used as fuel to meet the energy demand of the turbines onboard the platform.
Pipelines and subsea infrastructure
A 33km-long pipeline is laid between the platform and the Vesterled pipeline. This 6in gas import pipeline will supply the additional gas that is needed to meet the energy demands of the platform. Diluent to the platform will be supplied from the FSU through a separate 6in diluent import pipeline measuring 2.4km in length.
A 2.6km pipeline, with a 10in diameter, is installed to export the stabilised crude oil from the PDQ to the FSU.
A 6.5km umbilical and an export pipeline of the same length will connect the production template at the Mariner East to the PDQ.
All the pipelines are connected to their respective structures by pipeline end terminations (PLETs) and spools.
The 73km-long fibre-optic communication cable runs from the Heimdal platform, which is located on Block 25/4 of the Norwegian North Sea, to the Mariner platform.
Contracts awarded for Statoil’s project
The FSU is being built by Samsung Heavy Industries in South Korea. Wärtsilä supplies pumping solutions for the FSU.
Front end engineering and design (FEED) of the PDQ’s topsides was carried out by Aker Solutions as part of a $39m contract that was awarded in late-June 2011. SNC-Lavalin was contracted in November 2011 for the FEED of the platform’s jacket.
The heavy-lift operations for the project are being carried out by Saipem.
The engineering, procurement and construction (EPC) contract for the steel jacket has been awarded to Dragados Offshore who works in collaboration with SNC Lavalin. The contract for the platform’s topside has been awarded to Daewoo Shipbuilding & Marine Engineering (DSME). CB&I og Rig Design Services (RDS) assists DSME.
Odfjell Drilling provides drilling services for the project, under a contract worth £160m ($245m) awarded in April 2013.
Subsea 7 was awarded a $170m engineering, procurement, installation and construction contract for 24 miles (38.6km) of rigid flowlines and flexible riser systems, and associated infrastructure and equipment.
Aker Solutions was awarded a contract in June 2014 to provide field maintenance and modification services. The five-year contract includes options for four-year extension and requires Aker to provide these services during the pre-operations phase and the hook-up and commissioning phase.
Schlumberger was awarded a contract to deliver the drilling and well services for the Mariner field.