Predictive permeability variations in a Hermod sand reservoir, Stine Segments, Siri Field, Danish North Sea

The Hermod sand of the Stine Segments, Siri Field, Danish North Sea, displays large permeability variations (1-600mD). These permeability variations represent horizontal layering in the reservoir, largely formed by diagenetic processes. They have a significant impact on reservoir performance, because horizontal producers in fairly thin reservoirs (similar to 30 m) are protected against bottom-water influx and can produce water-free for long periods of time. This paper presents the results of a detailed multidisciplinary study where the observed variation in permeability can be explained by two main diagenetic phases: silica, as opal cement and microquartz, and berthierine, a serpentine mineral that is closely related to chlorite. Opal/microquartz and berthierine cements dominate in separate parts of the reservoir bodies. Opal/microquartz cemented sands have high permeability (typically 500-600 mD). Berthierine cement has a different growth pattern in the oil and water zones, resulting in intermediate permeability in the oil zone (typically 50-100 mD) and very low permeability in the water zone (typically 1-10 mD). (c) 2008 Elsevier Ltd. All rights reserved.