Heather oil field
The Heather oil field is a significant crude oil producing field in the UK sector of the northern North Sea, 458 km north-north-east of Aberdeen. Production of oil started in 1978 and ceased in 2019. The Heather Alpha installation is currently undergoing decommissioning.
The field
The Heather oil field is located in Block 2/5 of the UK North Sea. It is named after the plant that grows extensively on Scottish moors. The Heather field was discovered in December 1973 and comprises a middle Jurassic sandstone at a depth of 9,800 to 11,750 feet. The reservoir and its fluids had the following characteristics:| Parameter | Value |
| Porosity | 1.7-19.3 % |
| Water saturation | 21.4-56.3 % |
| API gravity | 35°API |
| Gas Oil Ratio | 650 standard cubic feet/barrel |
| Sulfur content | 0.7 % |
| Recoverable reserves | 90-120 million barrels, 14.1 million tonnes |
Owners and operators
The initial owners of the field were a consortium comprising Unionoil Company of Great Britain, Texaco North Sea UK Ltd, Tenneco Great Britain Ltd, and DNO Ltd.. The field was operated by Unionoil Company of Great Britain. In 1994 the owners were BG Great Britain Limited, Texaco Exploration Ltd, Unocal Britain Ltd, and DNO Ltd. The operator was Unocal. In 1999 DNO became the operator, then Lundin from 2008, and finally Enquest.Development
The field was developed by a single integrated drilling, production and accommodation platform: Heather Alpha. The principal design data of the Heather A platform is given in the following table.| Installation | Heather A |
| Coordinates | 60°57’13”N 00°56’23”E |
| Water depth, metres | 143 |
| Fabrication substructure | McDermott, Ardersier |
| Topsides design | McDermott |
| Topside weight, tonnes | 22,000 |
| Function | Drilling, production, accommodation |
| Accommodation | 180 |
| Type | Steel jacket |
| Legs | 8 |
| Piles | 24 |
| Well slots | 40 |
| Throughput oil, barrels per day | 60,000 |
| Water injection, bpd | 100,000 |
| Platform installed | June 1977 |
| Production start | October 1978 |
| Oil production to | Ninian Central |
| Gas production to | Used onboard for gas lift and fuel gas |
Processing
The wellhead fluids flowed via the production manifold to the 3-phase Production Separator which operated at 65 psi. From the Separator oil was routed to another 3-phase Production Separator operating at a lower pressure of 35 psi. Oil then flowed to the crude booster pumps, through oil metering then by 32 km 16-inch pipeline to Ninian Central and thence to Sullom Voe. Produced water from the separators was treated by hydrocylones and a compact flotation unit to remove oil prior to overboard discharge. Vapour from the Production Separators was compressed, dried by TEG and further compressed to 325 psi for use as fuel gas and up to 1,480 psi for gas lift. In 1985 a connection was made to the Western leg gas pipeline, a 6-inch pipeline imported gas into Heather to augment gas supplies. Import gas flowed to an Import Gas Knockout Drum, through metering and to an Import Gas Heater.The oil production profile for Heather A in the early operating period is shown in the graph:
| Facility | Capacity |
| Crude oil | 30,000 bbls/day |
| Gas compression | 54 MMSCFD |
| Dehydration | 54 MMSCFD |
| Gas lift | 54 MMSCFD |
| Produced water | 50,000 bbl/day |
| Water injection | 70,000 bbl/day |