North Sea Reservoir Characterisation by Using Flow Units Technique: A Case Study

Abstract

An effective and sufficient description and characterisation of the reservoir are ultimately essential to successful reservoir engineering management. The integration of sufficient core analysis data is the primary target of reservoir description to permit identification of zones (Flow Units) with similar fluid-flow characteristics. The identification of flow units is the aim of integrated core analysis programme. The flow units technique is a method of characterising a reservoir and the route to flow unit and reservoir description is dependent on the core data available. This paper presents a practical application of the flow units technique to a classic North Sea reservoir using a statistical analysis for the flow zone indicator (FZI) to differentiate flow units. All laboratory work was conducted using 1 inch cores. Core analysis porosity-permeability data from 410 core lugs was used to work out the porosity-permeability relationship using the flow units technique. After flow unit characterisation, six flow unit groups have been selected, and sample of each individual flow unit were selected for mercury injection analysis using injection pressure up to 50000 psi. Finally, the pore size distribution and mean flow radius were calculated. In this paper, the application of this technique is discussed to examine how a better reservoir description can be achieved for a specific reservoir. This article describes a new attempt to apply this technique to a North Sea reservoir. The technique is more complex than either the depositional or layer model, but is also the most realistic because it takes account of the wide variety of geological and petrophysical characteristics present. The properties used to derive flow units in this reservoir were the core porosity-permeability and permeability measurements for small, medium and large pore- throat radii. The general porosity-permeability cross plot shows a large scatter, indicating poor overall correlation between porosity and permeability. However, by using flow unit technique, a reasonable relationship between porosity and permeability can be shown to exist for each individual flow unit. The flow unit technique provides a comprehensive reservoir description. Six flow units are defined; three of these exhibit good-to-excellent reservoir quality, one is good reservoir quality and two are poor reservoir quality. It can be said that this technique has been applied successfully to this particular case.