Trestakk Oil and Gas Field, Norway
Trestakk is an oil and associated gas field lying in the Norwegian Sea in block 6406/3. The field is located in production license PL091, approximately 27km south-east of Åsgard A. The water depth in the region is estimated to be 300m.
Statoil operates the field with a 59.1% ownership interest, while the other licensees are Eni Norway (7.9%) and ExxonMobil (33%). A concept for the field's development was selected in 2015 and has been approved by the Norwegian authorities.
Production from the field is scheduled to commence in 2019 after the completion of production drilling and modification work in 2018. Statoil is developing the field at an estimated cost of Nkr8bn ($975.7m). The life expectancy of the field is approximately 13 years.
Trestakk field discovery and reserves
The Trestakk field was discovered in 1986 by drilling the exploration well 6406/3-2, while an appraisal well, 6406/3-4, drilled in 1987 confirmed the presence of hydrocarbons.
The field is segmented into four divisions that belong to the Yarn structure. Located 4,000m below the sea level, the field's reservoir has medium pressure and temperature, and consists of Middle Jurassic sandstones in the Garn Formation. The shallow marine sandstones have calcite-cemented intervals and are identical.
Trestakk field holds 14.6 million cubic metres (Mm³) in resource oil and 3.7GSm³ in associated gas, and is expected to produce 22.2GSm³ of gas over its life time. Gas produced from the field will be injected into the reservoir with 18.5GSm³ of gas estimated to be injected into the reservoir.
Trestakk field development details
The field will be developed using five subsea wells, including three production wells and two gas injection wells, tied back to Åsgard A FPSO.
The installation will include two templates with four slots each with a direct link to Åsgard A. The northern bay frame will consist of three production wells, while the two gas injection wells will be located in the southern bay frame.
Recovered hydrocarbons will be processed at Åsgard A FPSO and the gas will be injected using the R-frame. A 25.2km-long production line with an inner diameter of 12.6in will connect the Trestakk field to the Åsgard A FPSO lying towards the south.
An electric heating cable will be installed on the production line that will link the southern bay frame to Åsgard B, via Åsgard A. It will be approximately 30.2km-long with insulation coating and will comprise chromium steel.
Åsgard A FPSO will also undergo modification as it will require a new flexible riser and associated subsea structures. The water produced from the field will either be injected into the reservoir or will be treated on Åsgard and then discharged to the sea.
A semi-submersible drilling rig will be used for drilling the wells that are expected to be completed in 640 days.
Key players involved
A contract for subsea front-end engineering and design (FEED) study for the Trestakk field was awarded to Forsys Subsea, a joint venture between FMC Technologies and Technip. The contractual scope includes all systems and related services from the wellhead to Åsgard A riser hang-off, including umbilicals, riser, flowlines and subsea production system installed and made ready for operation.
Forsys Subsea will also provide an optimal technical and cost-efficient development solution, along with a well-defined basis for the development phase under the terms of the contract.
Aker Solutions was selected to perform a front end engineering design (FEED) contract for the Trestakk field tie-in to the Åsgard A production vessel in the Norwegian Sea. The contract has an engineering, procurement, construction and installation (EPCI) option.