Modeling Geology from Static to Dynamic in the Eldfisk Chalk Field, Southern Norwegian North Sea

Thomas, Michel Claude¹, H. Alexandersen², Claus K. Clausen², Matthew G. Reppert² (1) Total E&P Norge, Stavanger, Norway (2) ConocoPhillips Norway, Stavanger, Norway

The Eldfisk field, located in the Norwegian Central Graben, is composed of two inverted anticline-type structures, Alpha & Bravo. Turonian to Maastrichtian chalks are the reservoir rocks with the best facies being the debris flows mainly expressed within resedimented chalk bodies of the Tor Formation. Porosity and permeability are facies related but effective permeability is increased as a result of locally intense fracturation, as in the neighbouring Ekofisk Field.

For preparation of the next Development Phase of the field, a Shared Eldfisk Team (SET) was composed among the partnership to build a new 3D Reservoir Model with as main objective “to input as much geology as possible”.

Detailed review and refinements of biostratigraphy, sequence stratigraphy, well-to-well correlations and core descriptions (sedimentary facies and dynamics) led to the establish­ment of Gross Depositional Environment maps per formation. Porosity-permeability trends were defined per formation and populated onto Geological Trend Maps (GTM). Porosity was derived from field-wide calibration of the Acoustic Impedance inverted seismic model. Effects from both diagenesis in the early depositional history and the present day “crest-to-flank” diagenetic behavior were taken into account for defining the rock-types and the poros-ity-permeability trends. Sw was then calculated and distributed from rock-types and related J-functions using tilted Free Water Levels per formation. Permeability, once defined by the Phi–K trend and populated using the GTM, was used as the fine-tuning parameter for the first calibration and history matches.

The work-flow and methodologies selected in this study made it possible to establish and further use the mapped geological model to populate the key parameters ensuring the geology to be honoured from the static to dynamic modelling of the chalk field.