Defining Vertical Permeability Distribution in a Steam Assisted Gravity Drainage Project: An Integrated Multi-Scale Approach to Modelling a Heavy Oil Reservoir

Peter Phillips and Renjun Wen
Geomodeling Technology Corp., Calgary, AB, Canada

The bitumen deposits in Alberta, Canada, comprise about 1,700 billion bbls of bitumen in place, with an estimated 174 billion bbls recoverable. The primary extraction method will likely be steam assisted gravity drainage (SAGD), a method dependent on vertical reservoir permeability. The Lower Cretaceous McMurray Formation, the dominant reservoir, is an estuarine channel and tidal bar system with significant lateral and vertical heterogeneity. Although tidal bar and channel sands exhibit great permeabilities, this reservoir exhibits relatively low permeability and porosity associated with abandoned channel fill and tidal flat lithofacies. The objective of this case study was to define barriers to steam migration by modelling vertical permeability distribution in the reservoir.

To represent large-scale reservoir permeability accurately, we developed and implemented a modelling and upscaling workflow approach that incorporated small-scale heterogeneities impacting fluid flow (see Figure 1). To identify metre-scale heterogeneity, we applied several techniques to the seismic data set, including spectral decomposition, attribute cross-plotting, and opacity filtering. We then incorporated the output into a reservoir-scale modelling tool, with grid geometries that reflected the deposition and the lithofacies distribution in the reservoir. To incorporate the effects of centimetre- to decimetre-scale flow barriers, we generated near wellbore models that simulated the bedding structures and lithology observed in core and inferred from well logs. We then applied flow-based upscaling to the models to derive facies-dependent effective properties, including vertical and horizontal permeability. We used these upscaled values to populate the geocellular grid model to derive overall effective directional permeability distribution within the reservoir.

The multi-scale modelling results honour core analysis, well log data, and seismic interpretation (see Figure 2), and provide useful input to reservoir production simulation tools. This multi-scale approach can be applied to other unconventional reservoirs to improve estimates of critical reservoir properties.

Figure 1. Near Wellbore Modelling Workflow.

Figure 2. Model Honouring Development in an Estuarine Channel Complex.

AAPG Search and Discovery Article #90075©2008 AAPG Hedberg Conference, Banff, Alberta, Canada