AAPG Bulletin, V. 82 (1998), No. 6 (June 1998), P. 1156-1172.

Stochastic Modeling of Incised Valley Geometries¹

Alister C. MacDonald,² Lars Magnus Fält,³ and Anne-Lise Hektoen⁴

©Copyright 1998.  The American Association of Petroleum Geologists.  All Rights Reserved

¹Manuscript received September 18, 1996; revised manuscript received May 8, 1997; final acceptance January 13, 1998.
²Statoil Research Centre, 7005 Trondheim, Norway.
³Statoil, Petek, 4035 Stavanger, Norway.
⁴Norwegian Computing Centre, P.O. Box 114, 0314 Oslo, Norway.

This work was primarily done during 1993 and 1994, and was first presented at the 1994 AAPG Annual Convention in Denver, Colorado. Statoil is acknowledged for permission to publish. A large number of people have contributed to the development and testing of the modeling procedure described in this paper. In particular, we would like to thank Arve Næss, Statoil; Lars Holden, Norwegian Computing Centre; Jan Inge Tollefsrud, Saga Petroleum; and Christian Brostrøm and Ulf Lægreid, NTNU, for input at various stages. T. C. Coburn, J. M. Yarus, an anonymous reviewer, and K. T. Biddle are thanked for reviewing the manuscript and providing proposals that improved the final product. 

ABSTRACT

A stochastic modeling procedure, designed to capture sequence stratigraphic principles, has been developed for modeling fluvial reservoirs where high-frequency base-level fluctuations have exerted a strong influence on reservoir architecture. Reservoir stratigraphy and architecture are defined by the successive simulation of two types of surfaces: base-level rise (flooding) surfaces and base-level fall surfaces (sequence boundaries). The flooding surfaces are modeled as standard two-dimensional Gaussian fields. Modeling sequence boundaries with incised valleys is more complex and required the development of a novel "object" modeling technique. This new model can be used to generate realistic valley geometries and is flexible enough to allow for complex multiwell conditioning.

The modeling procedure is illustrated using a test data set based on well interpretations from the fluvial Statfjord Formation in the Statfjord field of the Norwegian North Sea. The main reservoir sandstones were deposited in valleys defined by a sequence boundary at the base and a flooding surface at the top, whereas the main barriers to flow are mudstone-rich intervals deposited on unconfined alluvial plains. Five sequence boundaries and four flooding surfaces have been interpreted within an approximately 60-m-thick reservoir interval. Simulation of these surfaces using the new modeling procedure defines the three-dimensional distribution of reservoir units and barriers. The modeling procedure allows the simulation of realistic geometries that are in accordance with the geologist’s conceptual model for the reservoir. The models also provide an enhanced description of reservoir distribution and connectivity, and can serve as an improved basis for reservoir management, well placement, and predictions of reservoir performance in complex fluvial reservoirs.