UKCS: 300 MMboe in 30 yearsMariner field location. Source: JX Nippon

UKCS: 300 MMboe in 30 years

Equinor announced first heavy oil from the Mariner field in the UK North Sea, which is reported to have up to 3 billion barrels of oil in place.

The Mariner field, Equinor’s first operated field on the UKCS, is expected to produce annual average plateau rates of around 55,000 bpd, and up to 70,000 bpd at peak production until 2050.

The Mariner reservoirs have up to 3 billion barrels of oil in place, a 50% increase on what was originally assumed, and the estimated recovery rate has already been increased by 20%. The field is expected to produce more than 300 MMboe over the next 30 years.

The Mariner field is developed with a production, drilling and quarters (PDQ) platform based on a steel jacket, with oil being exported to a floating storage unit (FSU) and then to shore via tankers. As part of the development, around 100 wells will be drilled over the first 12-14 years.

Mariner is located on the East Shetland Platform of the UK North Sea in block 9/11, being operated by Equinor (65.11%), with JX Nippon (20%), Siccar Point (8.89%) and ONE-Dyas (6%) as partners.

Discovered in 1981, the Mariner heavy oil field was left untouched due to the complexity of the reservoir. It took new technology and new seismic data to find the right approach.

Paleogeographic maps of the Paleocene. A) Maureen Formation – the primary depocenter extended from the Outer Moray Firth Basin to the Central Graben, with an additional depocenter created in the hanging wall of the fault bounding the East Shetland Platform. B) Lista Formation – sandstone units are developed in the Outer Moray Firth Basin to the Central Graben area, and over the Viking Graben. Source: The Millennium Atlas Central and Northern North Sea

Mariner has two main reservoir units, and both are Paleocene sand sequences of excellent quality. The Maureen sands are comprised of stacked deltas and slope sediments. The Heimdal sands lie above the Maureen and consists of a complex, disrupted channel system that in addition have undergone soft sediment remobilisation and now form distinct stratigraphic ‘geobodies’.

Maureen seismic section. Source: Mariner Field: a challenging UK heavy oil development PPT, 2013 Equinor

Imaging is a challenge

The main challenge at Mariner was the mapping of the Heimdal sands. But also, the imaging of the subtle faults and calcite layers within the Maureen Formation is of great importance for the production development at Mariner.

Comparison of different seismic surveys over the Mariner field, showcasing the difficulty in imaging the Heimdal sands. Broadband 2012 is the most recent survey. The green curves show gamma-ray of nearby wells. The base of the thick Heimdal sand observed in the second well from the left ties most accurately to the Broadband multisensor data, and as such can be mapped with more confidence. Source: Improved reservoir characterisation by Multisensor Towed Streamer Seismic Data at the Mariner Field paper, 2014

3D seismic has enabled detailed reservoir mapping for both reservoirs with the Heimdal ‘geobodies’ being mappable as distinct volumes. Two exploration wells drilled in 2017 encountered oil filled Heimdal ‘geobodies’, confirming that additional ‘geobodies’ exist outside the main field area.

Equinor describes the project as a “digital frontrunner” where automated drilling, digital twin, field worker tools and digitised logistics were implemented to support operational and field maintenance planning.

The oil in Maureen Formation has an API gravity of 14.2, whereas the oil in Heimdal Formation has a  2.1 API gravity.

Mariner is one of the largest industrial projects in the UK in recent year, benefiting of a gross investment of more than $7.7 billion.