Tern Oil Platform: Infrastructure and Production Operations
The Tern oil platform is a specialized steel jacket production and drilling facility designed to extract and process hydrocarbons from the North Sea. Constructed by RGC Offshore at the Methil yard, the platform was officially installed in May 1988. While its primary purpose is to manage the Tern reservoir, it serves as a central hub for several other fields, ensuring efficient resource recovery and transport.
Key Facts
- Installation Date: May 1988
- Manufacturer: RGC Offshore (Methil yard)
- Structure Type: Steel jacket production and drilling platform
- Export Route: Brent System pipeline to Sullom Voe Terminal
- Integrated Fields: Tern, Hudson, Falcon, Kestrel, and Cladhan
- Peak Production (Hudson): 4.70 million tonnes per year
Production and Processing Workflow
The platform utilizes a complex system of separation trains to process well fluids—a mixture of oil, gas, and produced water—into exportable products. The Tern wellheads route fluids into two parallel systems: Train A and Train B.
Train A and Train B Operations
Train A employs a 3-phase Production Separator to divide the fluids into oil, gas, and produced water. The oil then moves to a 2-phase Dehydrator for further water removal before being cooled and pumped through a metering skid for export. Train B also uses a 3-phase Production Separator; however, the oil is cooled and pumped directly to mix with the output from Train A before final metering.
Hudson Field Integration
Fluids from the Hudson field are processed via a dedicated 3-phase Hudson Production Separator. The separated oil passes through a 2-phase Hudson Dehydrator and coolers, undergoing segregated metering before joining the combined stream from Trains A and B for export.
Gas Management and Export
Gas captured from the various separators is co-mingled and processed through three stages of compression. A portion of this gas is extracted after the second stage to be used as fuel. The remaining compressed gas is utilized for gas-lifting—a process of injecting gas into production wells to reduce the hydrostatic pressure and increase oil flow—for both Tern and Hudson wells. Finally, the gas is processed in a treatment packing before being metered and exported via pipeline.
Field Expansion and Timeline
Over the decades, the Tern platform has expanded its capacity by integrating several subsea tiebacks and nearby fields. The Hudson Field (located in block 210/24) began production via the platform in 1993, reaching a peak output of 4.70 million tonnes per year. This was followed by the Kestrel Field (block 211/21a), a small subsea tieback that started production in 2001. The most recent addition to the platform's operations was the Cladhan field, which began producing in 2017.
| Field Name | Production Start Year | Notes |
|---|---|---|
| Tern | 1988 | Primary reservoir and platform site |
| Hudson | 1993 | Peak production of 4.70 million tonnes/year |
| Kestrel | 2001 | Small subsea tieback (Block 211/21a) |
| Cladhan | 2017 | Latest field addition |
Logistics and Export
Once the oil is processed and co-mingled, it is exported to the Sullom Voe Terminal. This transport is facilitated by the Brent System pipeline, with the oil passing through the North Cormorant and Cormorant Alpha platforms. Produced water from all separators and dehydrators is treated on-site before being disposed of overboard.
Frequently Asked Questions
Who built the Tern oil platform?
The platform was built by RGC Offshore at the Methil yard and installed in May 1988.
Which fields are processed by the Tern platform?
The platform processes fluids from the Tern, Hudson, Falcon, Kestrel, and Cladhan fields.
How is the oil exported from the platform?
Oil is exported via the Brent System pipeline to the Sullom Voe Terminal, routing through the North Cormorant and Cormorant Alpha platforms.
What is the purpose of the gas compression stages?
The three-stage compression system provides fuel gas (from the second stage) and provides gas-lifting for the Tern and Hudson production wells to enhance oil recovery.
What was the peak production for the Hudson Field?
The Hudson Field reached a peak production of 4.70 million tonnes per year.