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 (1–600 mD). 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 (∼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).