Reservoir modelling of the Vlieland Sandstone of the Kotter Field (Block K18b), offshore, The Netherlands

Abstract

The Vlieland Sandstone reservoir of the Kotter Field has significantly outperformed the original production forecast. In view of an anticipated decline of the oil production, a geological re-evaluation was carried out in 1989-1990, with the aims of contributing to increasing productivity and improving sweep efficiency. Three closely related models have been developed. The Idealised Vertical Facies Association is a sedimentological model based on core material and represents an idealised vertical sequence of genetically related sedimentary facies. The model describes an overall regressive trend, produced by the progradation of a barred shoreface sequence, which is bounded top and bottom by transgression-related erosional surfaces. Within the reservoir interval, the trend described by the Idealised Vertical Facies Association is cyclically repeated. The Field Geological Layer Model forms the synthesis of the geological knowledge to-date and presents a three-dimensional description of the reservoir resulting from the integration of core, wireline log and seismic data. It is characterized by a minimum of four stacked regressive-transgressive cycles (each representing partial development of the Vertical Facies Association) and comprises a total of thirteen, geologically distinct layers. The Field Engineering Layer Model has been developed by modification of the Geological Layer Model in order to meet the specific input requirements of a reservoir performance simulation study and to improve cost-effectiveness. Up to the end of the geological modelling study (Dec. 1990), the results of the simulation study were satisfactory.