A method for evaluating the production scenarios in the delineation phase of an oil field is described, and illustrated with a synthetic example build from a Mesa Verde (Colorado) area outcrop. At delineation time, only a few wells and some geophysical surveys are available for reservoir characterization. The geologist analyses these data, and determines some major characteristics of the deposition system as its type, its direction, etc.

This interpretation is then quantified so as to be used as the input of a geostatistical simulation model, in terms of lithofacies proportion curves, and variogram function parameters. This quantification is not unique, and the geologist provides ranges for each parameter.

The geostatistical simulator gives several images, with different parameters varying in the selected ranges. A first investigation among these images is performed by looking at the volume of reservoir connected to the producing or injecting wells, for various wells spacing.

Then, these images are translated into petrophysical description, allowing to perform oil recovery calculations, for the selected images. Finally, an estimation of the oil production for different development scenarios, taking into account uncertainties is performed.

This methodology is possible thanks to a geostatistical simulation model enabling integration of geology and reservoir engineering.

The geostatistical simulation model is a tool for translating geological knowledge into parameters manageable for reservoir engineers. The proposed methodology allows to make better decisions in the delineation phase, as impact of uncertainty can be more easily computed.

The availability of an integrated model, avoiding painful data handling (petrophysical data attribution, upscaling), is an important point.

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