Early Operating Experience Of A Minimum Facilities Platform Designed To Process 20° API Eocene Crude Oil
Authors: Brown Gordon , Goodson R.J. 
Published: October 2008

This paper presents the challenges faced in designing topsides facilities to obtain economic development of the Alba Field, namely: low oil price; low crude versus very high produced water rates; 10w reservoir energy requiring artificial lift from day one and difficult oil water separation properties. The resulting design and its effectiveness is discussed based on early production experience. Lessons learned from the Alba Development will be applicable both to the development of other heavy oil reservoirs and marginal offshore prospects in general.

THE ALBA FIELD DEVELOPMENT

The Alba Field is located in Block 16/26 of the UK Continental Shelf, lying about 130 miles north-east of Aberdeen in 138 metres of water. The reservoir is a long, narrow Eocene aged sandstone deposit located at a depth of approximately 6,000 feet. The field was discovered in 1984 and field development plans were initiated in 1987. Because of the particular challenges presented by the Alba reservoir, devising a development solution that would provide an acceptable return on the investment was extremely problematic.

Alba is one of only four such heavy oil fields currently in production in the North Sea, the others being Emerald, the Helm/Helder/Hoorn cluster in the Netherlands and the Gryphon Field.

The development scenario selected was conceived in 1990 and favoured a phased development using separate production facilities in the North and South portions of the field. It was decided to proceed immediately with development of the Northern area, and based upon production experience, the Southern area would be developed some 5 years later. The selected export route was to a permanently moored Floating Storage Unit (FSU) with shuttle tanker operations transporting the produced oil to ports in Western Europe, The commercial viability of the field called for a minimalistic approach to platform design and a Minimum Facilities Platform (MFP) philosophy was adopted. First oil from the Northern Platform was achieved in January 1994.

THE ALBA CHALLENGE

The main challenge faced in the development of the Alba Field was to obtain an economic development from a field which required considerably larger and more complex facilities than other reservoirs of comparable size. The factors which led to the need for more complex facilities are summarised:The Alba crude is heavier and more viscous than the North Sea norm (API 20,6°API) and is relatively high in acid and metal content.The reservoir is almost totally underlain by water which is forecast to have an early breakthrough, resulting in very high produced water rates in comparison to the crude oil production rates.Water cut is expected to reach 70% within 4 years, rising eventually to 95%,The reservoir is relatively low in natural energy and whilst the wells will flow at low water cuts, artificial lift is required very early into the field life.The crude oil has a high viscosity (20 centipoise at 70°C) which significantly increased the complexity of the separation system design and the size of the process equipment.