VEJBAEK, OLE VALDEMAR
Geological Survey of Denmark and Greenland, Denmark.

Abstract: Clastic Reservoir Characterisation using Seismic Impedances and Geostatistics: Middle Jurassic unit of the Harald Field, Danish North Sea

Seismic impedances were applied to characterise a reservoir composed of clastic sediments, the Middle Jurassic reservoir unit of the Harald field in the Central Graben, Danish North Sea. Expected reserves (1996) are 7xl0⁶ m³ oil and condensate and 25xl0⁶ Nm³ gas consisting of two accumulations: an Upper Cretaceous and Danian Chalk unit located above a salt piercement, and a Middle Jurassic sandstone unit located in adjacent tilted fault blocks of considerable relief.

Because reservoir properties are linked to sedimentary facies, the facies distributions were analysed before we analysed porosity, key reservoir parameter. The reservoir characterisation uses an indicator conditional simulation technique, which produces stochastic simulations of reservoir properties beyond the control of hard data points. Well observations and seismic impedances condition geostatistical simulation of facies as well as, porosity. In addition transgressive trends and facies associations were honoured. Only three wells were available to condition simulations due to the field being at an early stage of development. Given a cell size in the characterisation of 20x20x6 m, the characterised number of cells is about four orders of magnitude greater than the number of cells checked by wells.

Characterisation results can be used to map hydrocarbons in place because modest effects of capillary forces produces simple relationships between porosity and water saturation linked to rock type.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas