Virtual outcrop models and their value for building geocellular models: An example from the windermere turbidite system (British Columbia, Canada)

Abstract

A Virtual Outcrop Model (VOM) is a three-dimensional, photorealistic representation of the exposed geology of a specific area, and consists of a georeferenced digital terrain surface rendered with high-resolution imagery. This cutting-edge technique is especially useful for outcrop studies where the extraction of accurate geometric data is the primary objective. In addition, using a VOM, petroleum geologists have the opportunity to study geobodies in a reservoir analogue from different perspectives (3D visualization), to map and correlate key stratal surfaces, and to compare the digital outcrop with other field data (e.g. sedimentary logs, stratigraphic surfaces, outcrop gamma-ray logs). A virtual outcrop also provides a revolutionary tool for building outcrop geocellular models. A geocellular model is a computer-based representation of a geological volume, which in most cases represents a subsurface reservoir. An outcrop-based geocellular model is similar, but constrained by outcrop data such as mapped surfaces and logs. The same software that is routinely used in the oil industry to build subsurface reservoir models can be adapted to manipulate data extracted from the VOM to build models of the outcrop (e.g. RMS by ROXAR, Petrel by Schlumberger and GoCad by Paradigm). In a typical workflow, stratigraphic surfaces are digitized in a VOM and exported into RMS. Once recreated in 3D, these surfaces are used to define zones where lithofacies and/or objects (geobodies) can be modeled. Lithofacies and geobodies are then used to control the distribution of petrophysical properties within the model, which can eventually be interrogated both statically and dynamically. Results from these analyses can provide important insights and improve input variables to build more realistic subsurface reservoir models. In this contribution we present an innovative method for the creation of a virtual outcrop model for strata of the Windermere Supergroup at Castle Creek (west-central British Columbia). The virtual outcrop model was created by draping high-resolution aerial images onto a topographic model, and then integrating this aerial dataset with ground-based laser scanning surveys of the cliffs that were not clearly represented in the aerial imagery. The utility of this VOM for subsurface studies is illustrated by the ability to show that accurate geometric data can be extracted from the outcrop model and imported into a reservoir modelling package. This aids in the recreation of zone boundaries in an outcrop-based “reservoir” model of a seismic-scale channel-levee system.