Subsea Processing - The Solution to Cost Efficient Deepwater Field Developments
Authors: Chiesa Giovanni , Eriksen Remi 
Published: October 2008

Subsea processing offers several advantages compared to traditional ways of producing, processing and transporting well fluids to onshore terminals. By removing the need for expensive, manned floaters, initial investments can be reduced significantly. A concept based on subsea processing also offers the option to provide additional energy to the well stream to reach treatment facilities (offshore or onshore). This is particularly important for exploitation of hydrocarbon reservoir in deepwater, where the needs for providing energy to the well stream is higher. This has the potential benefit of increasing the ultimate recovery and/or accelerating the production.

Regardless of the chosen concept, the ability to keep wells on stream is the most important factor determining field economic performance. For subsea processing, the anticipated equipment performance and the associated operating costs are subject to uncertainty. In addition, moving into deeper water, subsea interventions become more expensive and are associated with longer waiting times for the required intervention vessels.

The fundamental question is whether the reduced CAPEX of a subsea processing system is out-balanced by the higher OPEX as compared with traditional systems. Ultimately this question can be addressed using a cost/benefit approach. This paper discusses the advantages and disadvantages with subsea processing systems from a life cycle cost perspective (capital and operating expenditures), and describes how implications of component failures can be factored into business decision analyses that seek to evaluate the viability of new technology. In particular a review of the subsea processing technology provided by the industry today is given together with an overview of the new functionality that is required to make subsea processing a viable option for the exploitation of hydrocarbon reserves. The paper will identify areas of uncertainty related to subsea processing and define a rational approach to support the decision making process in the qualification of subsea processing solutions.

1. Introduction

Oil and gas production from deepwater fields is expected to significantly grow in the next three to five years with a substantial increase in the share of the total offshore production.

Produced fluids transportation in deep water is often challenged by a number of factors that can make the field exploitation economically marginal. The reduction of the well back pressure and the possibility to efficiently address the typical flow assurance issues associated to multiphase transportation can contribute to the economical attractiveness of the development of deep water fields.

Subsea processing has been contemplated for a number of years now as a viable option through the adoption and / or combination of novel technologies including mudline two / three phase separation, subsea multiphase and liquid pressure boosting.

Mudline separation can be based on either two or three phase separation and on pressure boosting to dispatch the liquid phase(s) to the receiving facilities. In particular, two phase separation enables the reduction of the well back pressure by free flowing the gas phase and boosting the liquid phase only.