Economic Evaluation of Subsea Development Options for the Future of the North Sea
Authors: Jenner G.P. , Tweedie J.A. , Ford J.T. 
Published: October 2008

ABSTRACT
The Northern and Central North Sea is a major oil and gas producing area. However as the region becomes more mature, the size of the fields is found to be decreasing. This paper analyses the technical options and cost of developing these smaller fields.
This work highlights that the future development of reservoirs in the Northern and Central North Sea will require extensive use of subsea production systems. Although the work was carried out in the summer of 1989, and therefore reflects the economic situation at that point in time, it does present a structured analysis of small field development potential.

1. INTRODUCTION
The Northern and Central North Sea is a major oil and gas producing area and will be for some time in the future. The amount of undiscovered reserves is estimated at between 4,000 and 13,000 million bbls(l). However as the region becomes more mature, the size of the fields is found to be decreasing. In order that these fields maybe economically developed it will be necessary to use subsea development techniques. There are a range of these techniques available and this paper describes a techno-economic evaluation of these techniques.
On the basis of historical and statistical data an indication of the number of undiscovered fields and their fundamental characteristics (reserves, distance to existing facilities and water depth) is developed.
A typical field is modelled on the basis of these characteristics and then a range of potential subsea development schemes (Fixed Platform, Subsea Tie-back, Semi-submersible with CALM and FSO, Semi-Submersible with Pipeline Export and FPSO unit) are costed, using typical (1989) cost data for the North Sea. Having established the base costs for each development, sensitivity analyses are performed to show the importance of technical and economic parameters.

2. ANALYSIS OF FIELD CHARACTERISTICS
In this section of the paper, published data for yet-to-develop fields and discoveries in the Northern and Central North Sea(l, 2,3,4,5) are analysed. From this data and the estimated undiscovered reserves (between 4,000 and 13,000 million bbls) we have developed an approximation of the number of undiscovered fields and their fundamental characteristics (reserves, distance to existing facilities and water depth).

Reserves
As already stated, it is estimated that between 4,000 and 13,000 million barrels (mmbbls) of oil still remain undiscovered in the sedimentary basins of the Northern and Central North Sea. This figure is of course continually updated and is based on analysis of both exploration data and an ever increasing understanding of the basins' geology,
Analysis of discovered but yet to be developed reserves data for the North Sea gives a distribution of small field sizes as shown in Table 1. For the purposes of this paper the term, 'small reservoirs' refers to reservoirs containing up to 100 mmbbls recoverable reserves. The table shows that over 75% of the yet-to-develop fields have less than 100 mmbbls of recoverable oil which corresponds with predictions that 80% of future discoveries will have reserves of less than 100 mmbbls(6).