Abstract

The 1st Eocene heavy oil reservoir (1E) in the Wafra field is a candidate for steamflooding due to its world-class resource base and low estimated primary recovery. However, industry has little experience in steamflooding carbonate reservoirs, which has prompted staging of several 1E steamflood tests, the latest of which is the Large Scale Pilot (LSP) started in 2009. To assist in facilities design, help understand expected performance in a very heterogeneous reservoir, and provide input to early decision analyses, numerical thermal simulation was used to generate probabilistic forecasts. Once adequate pilot history was available, the model was validated using probabilistic methods.

The LSP model was comprised of 1.5 MM cells, which allowed maintenance of adequate resolution and proper boundary conditions in the pilot area. Parallel computation enabled a probabilistic workflow to be implemented with this large thermal model.

In this paper we highlight the methodologies and inputs used to generate the probabilistic forecasts and validate the model. Major results of this work include the following: 1) in contrast to many green-field forecasts that are often optimistic, the LSP forecasts were instead conservative, likely due to unique aspects of the forecasting methodology, proper selection of uncertainty ranges, and the relatively high density of input data for model construction, 2) wide variations in production metrics were forecast, indicative of a highly heterogeneous reservoir, and 3) despite this heterogeneity, oil recovery mechanisms and recovery levels were comparable to those observed in steamfloods in sandstone reservoirs.

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