Integrating Multiple Parameters to Assess Reservoir Connectivity Uncertainty

Alan Irving¹, Emmanuel Chavanne², Vincent Faure³, Philippe Buffet³, and Eurico Barber^3
1Geoscience Research Centre, Total E&P UK, Aberdeen, United Kingdom
²Geoscience Technologies, Total SA, Pau, France
³Operations & Geosciences, Total E&P UK, Aberdeen, United Kingdom

Studies to assess uncertainty on connected volumes and forecast production typically include sedimentary properties such as net to gross, porosity and permeability within a fixed grid geometry. In many cases, however, uncertain structural parameters like fault and horizon location and fault permeability may be of comparable importance. Geometric uncertainty is typically ignored, while faults are considered as open or sealing or, at a later stage, used as tuning parameters to obtain a match to production history at the expense of physical realism.

We describe a workflow that combines existing tools for stochastic simulation of reservoir structure and properties to generate multiple equiprobable model realisations. Geometric parameters that may be varied include fault shape and location, horizon shape and location and, by implication, fault displacement and cross-fault juxtapositions. Property variables include fault zone architecture and permeability as well as conventional grid properties like net to gross, porosity, permeability and water saturation.
Commercial 3D earth modelling software provides the platform to manage parameter definition, stochastic simulation and volumetric calculations. Realisations can be ranked by volume or using different connectivity measures before selected models are submitted for flow simulation. Experimental design techniques can be used to analyse production sensitivity to different uncertain variables, aiding development decision making and production history matching.

The workflow is illustrated using two field cases; a simple tilted fault block gas accumulation producing by natural depletion and a more complex field containing oil production and water injection wells. Field-specific and more general conclusions can be drawn about the effect of different parameters; potential improvements and extensions to the workflow are discussed.

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