Subsea Processing - Maximising Value In Areas With Existing Infrastructure
Authors: Fjøsne Erlend 
Published: October 2008

In oil and gas regions throughout the world, marginal oil and gas discoveries normally exist 10 to 100 km from existing, producing infrastructure. The existing installations are anywhere from the early start-up phase of production through mid-to late life or into the final tail-end phase. Depending on the phase, there are potentials for improved infrastructure utilisation by targeting the challenges related to limited topside processing capacities or decreasing wellstream input.

The scope of this Paper is to describe the power of utilising Subsea Processing in combination with existing infrastructure in the area to significantly improve field economy, and also as a means to enable economical tie-in of marginal fields into extended reach areas.

Introduction

Subsea Processing has been an emerging technology in the Oil&Gas business for a number of years. There is no generally accepted definition of the term, and therefore some dissension exists, as to whether this is proven technology or if substantial development is still required.

To date, a number of Subsea Multiphase Boosting Pumps have been in operation for several years, as have Electrical Submerged Pumps. The VASPS (Vertical Annular Separation Pumping System) which is a gas/liquid separation & liquid boosting system, has been operating by Petrobras offshore Brazil since late 2001. Also, the Troll Pilot in the North Sea has been in full operation for the nine last months, demonstrating full scale subsea separation and injection.

The basis of this Paper is therefore that subsea separation, together with liquid and multiphase boosting, is becoming a mature and proven technology, and that time is now ready for identifying the full set of potential economical applications.

By looking at the life cycle of typical offshore infrastructures and surface production facilities, and by analysing why full utilisation of these is not achieved, potentials are shown for applying Subsea Processing to significantly improve the economy of infrastructure investments as well as of neighbouring satellite fields.

In the discussion it is not differentiated between dry well and subsea well based installations, as some, or all of the potentials are valid for both, or for combinations of both. However, some of the arguments given may not always be equally valid for dry well installations.

Similarly the discussion of the various principles does not specifically discriminate between oil fields or gas fields, as very often this must be evaluated on a specific case to case basis.

Potentials of improved infrastructure utilization

The infrastructure required for producing hydrocarbons offshore typically comprises a number of well completions, surface processing facilities such as platforms or floaters, and a means of transport, such as pipelines or tanker shuttles. Onshore facilities are sometimes also part of the necessary infrastructure.

When production from identified reserves is planned, the capacity - and therefore cost - of the infrastructure must be balanced between the expected yield of the wells and the overall field economy.