Abstract

Production of gas from remote offshore areas requires cost efficient solutions for boosting of the well-stream to maintain satisfactory flow rates throughout the field lifetime. As a result of emerging subsea processing technology, subsea gas compression has matured as a field development building block. The potential benefit of this technology is that it can eliminate the need for surface production facilities and facilitate production from reservoirs otherwise not seen economically attractive.

Development of subsea gas compression solutions is associated with substantial technical challenges. Several key components are well known from surface applications but need to be designed differently to meet the special subsea requirements.

Special attention is needed for the design of the compressor and motor unit, control and power distribution system, as well as other process equipment such as for separation, cooling and pumping. All these elements are needed to successfully exploit the full benefits of subsea gas compression.

This paper addresses some of the technical challenges associated with subsea gas compression and presents R&D focus for closing the technical gaps.

Introduction

Subsea processing has emerged as an interesting field development tool with the aim to achieve more economically attractive ways to produce oil and gas from the reservoirs. Various technologies have shown possibility to enable increased recovery for less cost. This is an evolution that follows the breakthrough of subsea production systems that have been successfully deployed to a large extent for many years.

Subsea processing can be defined as any active handling and treatment of produced fluids at or below the seabed. However, the the following processes are given most attention:

  • Multiphase boosting / pumping.

  • Separation processes.

  • Gas boosting / compression.

Examples of typical benefits achievable by including subsea processing as part of the field development are possibilities for:
  • Reduced total CAPEX, e.g. by reducing or eliminating topside processing and / or pipeline cost.

  • Accelerated and / or increased production and / or recovery.

  • Enabling marginal field developments, especially (ultra) deepwater fields and fields with long tiebacks.

  • Extended production from existing fields.

  • Enabling tie-in of satellite developments into existing infrastructure by removing fluid handling constraints.

  • Improved flow management, e.g. by use subsea water separation as hydrate prevention strategy.

  • Reduced impact on the environment.

These factors are valid to various degrees for different field development scenarios. These are the background for the evolution of subsea processing and gas compression technology, which is focused in this paper.

Evolution of subsea processing technology

The technical status of the main alternative subsea processing solutions is listed in Table 1. The table summarises the technical status of the technology based on both completed development and qualification activities as well as on present experiences from subsea applications.

Table 1: Technology maturity overview of the main subsea processing technology alternatives. (Available in full paper)

Multiphase boosting is by far the most mature subsea processing technology. Several applications have successfully been set in operation. The technology is now seen as proven and is included as a natural element in the planning of the solutions for relevant field developments.

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