SWorld First Submerged Testing of Subsea Wet Gas Compressor
Authors: Knudsen Tor Willgohs , Solvik Nils Arne 
Published: May 2011

As Statoil and other companies find and develop oil and gas reserves in more remote, deep and harsh locations, in some cases with more challenging reservoirs and fluid properties, the technological challenges, qualification requirements and technical risks of deploying subsea compression will all increase. However the business upsides of subsea compression will also increase and there will almost certainly be areas where subsea compression becomes an enabling technology, without which fields cannot be profitably developed.

The challenge of increased recovery in development of fields in remote location, deep water and fields located in harsh environments, implies the need for a proactive technology strategy. It is part of Statoil's strategy to actively drive the development of subsea gas compression to a technical readiness level where subsea gas compression can enable subsea gas fields, both from a technical and commercial point of view.

This paper summarises the results from rich gas subsea Technology Qualification Program (TQP) completed for Statoil's Gullfaks 2030 Subsea Compression project (GSC) in Norway applying Framo Engineering's WGC4000 compression technology.

The paper will focus on the results and conclusions from the TQP that has been ongoing during the last two years. The Gullfaks 2030 Subsea Compression project business case and the subsea compression system design will also be presented.

In May 2009 Statoil entered into a two year technology qualification contract with Framo Engineering AS for the engineering, manufacturing and testing of a full scale subsea gas compression system. This multiphase compressor has completed rigorous tests with hydrocarbons to prove that it meets the hydraulic capacity and is otherwise suited for Gullfaks' field design requirements.

The system described in this paper is currently being matured in parallel with other subsea and topside compressor systems.

The Gullfaks South Fields comprises several subsea satellite fields tied back to the Gullfaks A and C platforms. If a subsea compressor concept is selected, Statoil plans to install the subsea compression system close to two of the subsea production templates at the Gullfaks South field. This will boost the flow of gas towards Gullfaks C, and will both accelerate the total production, increase the total recovery rate and delay or eliminate the need for conventional low pressure production phase.

The important role of full scale testing, Statoil's technology qualification program and close collaboration with key technology suppliers is further described.

The Gullfaks field in general

The Gullfaks Field (Figure 1) is located in 135-220 meter water in block 34/10 on the Norwegian continental shelf, 175 kilometers north-west of Bergen. It covers 51 square kilometers and is developed with three large concrete production platforms, Gullfaks A, B and C (GFA, GFB and GFC), and several subsea production system templates.

Discovered in 1979, Gullfaks South contains oil, gas and condensate in two formations (Statfjord and Brent) Early production and first oil to the Gullfaks A platform came from subsea satellite wells and started December 22´th 1986.

Later the field was developed further with mainly four slot subsea templates in three phases, Gullfaks Satellites Phase 1, Phase 2 and Skinfaks Rimfaks IOR.

Phase 1 subsea production started October 10´th 1998 from a new generation of subsea production facilities. A complex reservoir structure, large volumes of associated gas and technical challenges such as high wax content in the oil have been among the most challenging factors.