Balder, North Sea Northern, Norway

Balder is located in blocks 25/10 and 25/11, 165km west of Haugesund, in a water depth of 125m. The field was discovered in 1967, but it was only during the appraisal drilling in 1974 that the major part of the field was discovered. Water depth in the area is 127m. Esso is the operator and sole licensee. The field’s licence period expires in 2011.

RESERVES

In this development phase, the field is estimated to provide recoverable reserves of 171m barrels of oil and 0.8 billion m³ of associated gas. The reservoir is highly problematic as it has very viscous oil, at a 20API specific gravity. Reservoir pressure is 177bar and the temperature is 77°C. Oil has been discovered on the nearby Ringhorn (10km north) and Forseti (7km north) prospects, and both oil and gas have been found on the Hanz prospect (15km south).

TEST PRODUCTION

In 1991, the field produced some 800,000 barrels of crude during a five-month extended well test, using Golar Nor's production ship Petrojarl 1.

PRODUCTION

Balder is one of first fields on the Norwegian continental shelf to be developed by means of a permanent floating production unit (FPU) vessel. During the production period, the Balder FPU will produce a total of 171 million barrels of oil. Although Balder's gas will initially be reinjected, Esso has requested of the authorities that the gas be subsequently routed through Statpipe.

WATER INJECTION

To maintain pressure and enhance oil recovery, produced groundwater from the water source well is injected into the reservoir.

PRODUCTION VESSEL

The Balder FPU vessel contains the facilities required for both the processing and storage of crude oil. The vessel is 211m long and 36m wide. It has a storage capacity of 380,000 barrels of crude, which is offloaded via shuttle tankers connected temporarily to the production vessel's stern. Loading from the Balder FPU can take place in a sea state with waves up to 5.5m in height. It can offload at a capacity of 31,500 barrels per hour.

The Balder FPU has ten crude oil tanks: eight located aft and two in front of the turret. In addition, it has a double bottom and double sides, as well as single longitudinal and transverse bulkheads. It is designed for continuous field operations for a minimum of ten years and is capable of operating in 70-100m water.

SUBSEA SYSTEM

The subsea system selected for Balder consists of up to 15 subsea wells. Each well includes its own independent guidebase, wellhead system and subsea tree. Some of the production wells are commingled and share a common flowline and riser. Wells are grouped at four field site locations with an electrohydraulic control umbilical from the Balder FPU to each field site. The riser and flowline layout is designed to avoid interference with the FPU's mooring system.

All seabed-to-vessel lines - both mooring lines and risers - pass through the turret, which is positioned just in front of midship. The vessel keeps stationary by means of ten anchors.

PROCESS FACILITY

The process facility is located behind the turret and has a peak capacity of 83,000bbl/day. The process facility includes a process train with a three-stage separation process. All process and utility equipment is built as complete modules. This includes an oil separation and produced water-treatment system, compression and gas reinjection, power generation, water injection, oil metering, chemical injection, ventilation, heating and cooling systems, and a flare.

The living quarters provide accommodation for 60 people. A power supply is provided from separate generators, using the produced gas or diesel as fuel.

PRODUCTION START-UP

The production vessel came on-stream in September 1999 and is producing at a rate of 80-90,000b/d.