The Logger Field: Reservoir Architecture and Heterogeneity

Abstract

The Logger field is a Conoco-operated oil field located in Block L16a in the Broad Fourteens Basin in offshore Netherlands. It is a small accumulation in which oil is trapped in a complexly faulted overthrust anticline. The producing reservoir is Lower Cretaceous barrier sand less than 30 m thick. Logger first produced oil in August 1985, and has moved into the decline phase since 1988. However, better than expected performance of this reservoir together with the need to maximize recovery provided the impetus for a detailed geological study of the reservoir, using cores and logs, and integrated with production data and structural reinterpretation. The study was completed in 1990 and has led to a practical layered reservoir geological model that has since aided simulation studies on the reservoir performance and further field-development planning. It has also resulted in an understanding of the geological controls on fluid movements. The reservoir architecture has a layer-cake construction consisting of up to 5 layers, each characterized by grain size, degree of bioturbation, organic contents, and permeability distributions. A number of carbonate concretions were found near the layer boundaries. They form internal permeability barriers to vertical fluid flow. Thin-section and minipermeability studies have further revealedmore » the presence of micro-scale heterogeneities within the layers. The primary control on reservoir quality variations is related to depositional facies. In this paper, the anatomy and observed heterogeneity of the Logger reservoir are presented.« less