ABSTRACT: Integrated Seismic Modeling of the Troll West Area

BLANGY, J. P., Stanford University, Stanford, CA, S. STRANDENES, Norsk Hydro A.S., Norway, and A. NUR, Stanford University, Stanford, CA

An integrated geophysical model of the reservoir sands was developed in several stages and forms the basis for detailed seismic characterization.

A rock physical model was derived from descriptions of the intrinsic properties of the reservoir sands (mineral constituents, in situ state, and on fluid content). The reservoir sands are loosely consolidated subarkosic to sublithic sands, with porosities between 25% and 40%, and permeabilities from 1 d up to 30 d. Elastic velocities were measured on 38 core samples under various conditions and were related to the petrophysical observations.

Log and core data were integrated. Velocity dispersion can be neglected to first order in these sands. Ultrasonic and sonic measurements together with petrographic analyses provide a detailed knowledge of the rocks at the micro scale. The next step consists of upscaling the rock properties to seismic wavelengths. Once equivalent, transversely isotropic long wavelength properties have been established, the petrophysical-based model was used to link lithologic parameters with seismic data for a better characterization of the quality of the reservoir sands.

Interpretation of a 3-D seismic survey provided the structural and stratigraphic framework for detailed integrated seismic analyses. Detailed pre-stack reflections were modeled and used to evaluate the effects of mica content, and carbonate "bones" on the seismic response. The effects of changes in the amount of transverse isotropy induced by fine layering of calcite cemented "bones" within the reservoir were evaluated by comparisons of pre-stack responses; AVO

responses of good and bad oil/gas sands were compared, and the effects of changes in the properties of the seal and its thickness were assessed. Because the sediments are loosely consolidated and exhibit a small amount of diagenesis, we also related the permeability of the reservoir sands to the seismic, through porosity and textural information.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)