STOCHASTIC MODELING OF INCISED VALLEY GEOMETRIES

A stochastic modeling procedure, designed to capture sequence stratigr aphic principles, has been developed for modeling fluvial reservoirs w here high-frequency base-level fluctuations have exerted a strong infl uence on reservoir architecture. Reservoir stratigraphy and architectu re are defined by the successive simulation of two types of surfaces: base-level rise (flooding) surfaces and base-le-c el fall surfaces (se quence 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 :''ob ject'' modeling technique. This new model call be used to generate rea listic valley geometrics and is flexible enough to allow for complex m ultiwell conditioning. The modeling procedure is illustrated using a t est 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 b oundary at the base and a flooding surface at the top, whereas the mai n 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 int erval, Simulation of these surfaces using the new modeling procedure d efines the three-dimensional distribution of reservoir units and barri ers. The modeling procedure allows the simulation of realistic geometr ies that are in accordance with the geologist's conceptual model for t he reservoir The models also provide an enhanced description of reserv oir distribution and connectivity, and can serve as an improved basis for reservoir management, well placement, and predictions of reservoir performance in complex fluvial reservoirs.