At the Nexen Long Lake in situ steam-assisted gravity drainage (SAGD) oil sands recovery project, the bitumen-saturated reservoir is in the Lower Cretaceous McMurray Formation. The main depositional environment in the reservoir unit is fluvial-estuarine meandering channels. Stacked channel deposition exhibits a high degree of variability both vertically and laterally over short distances and depositional complexity occurs at many scales. Many papers have been written on characterizing oil sands deposition geologically or geostatistically. However, complete characterization cannot be achieved at all scales due to the degree of complexity.

Building a history-matched geomodel can be very time consuming and very challenging in complex reservoirs such as in Long Lake, where the Quaternary (Gregoire) Channel, collapse features, top gas and top water, lean zones, as well as shale barriers and baffles, contribute to the complexity. This paper presents a practical geological modeling approach used at Nexen to quantify uncertainties of reservoir properties. This approach has been validated by history matching and prediction. The solution is based on the integration of all available geology, geophysics, petrophysics, reservoir engineering, and production information. Using the proposed solution, the number of modeling iterations and the time required to achieve the desired objectives of history matching and prediction have been significantly reduced.

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