Ole Eirik Berge2,
Geir Vaaland Dahl3,
(1) Schlumberger OFS research, Stavanger, Norway
(2) Norsk-Hydro, Bergen, Norway
(3) Schlumberger OFS research
Abstract: Facies and Fluid Mapping in a Heterogeneous Reservoir using 4C data, Case study from the OSEBERG field
Optimally placed wells have a high impact on the potential depletion of a given reservoir. The focus of this paper is to demonstrate that 4C seismic technology can be a key element in this process. Since shear-waves are insensitive to the type of pore-fluid the first step in the proposed reservoir characterization procedure is to map the lithologies from the shear- waves. The second step is to use the pressure- wave information to invert for the pore-fluid types constrained to a given lithology as output from step one. The different seismic attributes are fed into a multi-attribute statistical and neural network classifier, using well data as control points (training data).
Results from the Oseberg field (North Sea) will demonstrate that the procedure can be applied with success on a heterogeneous reservoir (Middle Jurassic Ness Formation). Significant amounts of the total oil in place are expected within fluvial channel sandstones that are encased within surrounding nonreservoir lithologies. One of the main challenge was to discriminate between coal beds and oil-filled sand using 4C seismic. The compressional acoustic impedance response of these two cases is similar and it is not possible to distinguish between the lithological effects and the fluid effects. The field is stimulated with gas-injection, which is an additional challenge since the gas effect on the P-waves completely dominates the seismic response. This study has shown that detailed seismic attribute analysis and classification is able to provide sandstone distribution maps and fluid indicator maps for this complex reservoir unit.
AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana