New Technology Enables Development of Norwegian Sea Field
Authors: Carpenter Chris 
Published: July 2019

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 29523, “New Technology Enables Development of Field in Norwegian Sea,” by Arne Skeie, Subsea 7, prepared for the 2019 Offshore Technology Conference, Houston, 6–9 May. The paper has not been peer reviewed. Copyright 2019 Offshore Technology Conference. Reproduced by permission.

The Arfugl field is a gas condensate field located in the Norwegian Sea. Heat input into the flowline system is required during shutdown and potentially also during off-plateau production periods. A new enabling technology known as electrically heat-traced flowline (EHTF) will be used to enable system startup and shutdown and to maintain production fluids outside of the hydrate envelope during steady-state operation.

Background

EHTF is a pipe-in-pipe (PIP) system in which heating cables are used to heat the inner pipe. This enables even longer tiebacks and development of fields with challenging hydrate characteristics. The Arfugl field represents one of the first EHTF projects awarded.

System Configuration

Topside. The Arfugl field will be tied back to the Skarv floating production, storage, and offloading (FPSO) unit. A container module with a transformer will be installed on the FPSO. From the transformer, the required three-phase voltage can be taken out by a tap exchanger. The three phases are then routed through the swivel paths to the turret, where they are split into multiple triplets in a busbar box. One swivel path is also occupied by fiber-optic (FO) cable, which is used for digital temperature•monitoring.

Umbilical. The triplets are routed from the busbar box though the dynamic and static umbilical to the subsea umbilical termination assembly (UTA). The UTA is located close to the inline power-inlet structure (ILPIS), which is the entry point for the power into the flowline. Electrical flying leads are used to connect the UTA to the ILPIS. The FO is also routed through the umbilical and connected to the ILPIS by flying leads.

ILPIS. The ILPIS is shown in Fig. 1. The flying leads from the UTA are connected to wet-mate connectors on the roof panel. In addition to the flying leads for power, two dedicated flying leads for the FO are included. From the wet-mate connectors to the double barrier arrangement, the wires are routed through oil-filled hoses with overpressure. In the double barrier, the wires are routed through two penetrators; the first enters into a chamber with atmospheric pressure, and the second into the annulus, where pressure is lower than atmospheric pressure. Should one barrier begin leaking for any reason, there will always be an active second barrier. The ILPIS is located in the middle of the 20-km flowline.

Flowline Cross Section. From the ILPIS, the wires are routed onto the inner pipe in a helix shape, which ensures that the wires do not experience excessive tension or compression during the reeling operation when the flowline is installed (Fig. 2). The inner pipe is a 10-in. pipe inside a 16-in. carrier pipe. Centralizers are also located on the inner pipe.

The pressure is reduced in the annulus between the inner and outer pipe to improve insulation. Insulation panels are located on top of the heating wires. The insulation panels consist of a microporous material, which means that, when pressure is reduced, the voids in the material become so small that movement of air molecules is restricted, and thus insulation properties are improved.