Uncertainties particularly in geological parameters are always present and can be significant if associated with field development. These uncertainties could be perceived by geologists and engineers to exist in the available data. Industry has been using uncertainty analysis to identify, address and mitigate risk. Development strategies and well placement may significantly depend on field geology, maturity of the depletion stage, technological factor, drive resources and other parameters. Well placements optimization most of the time is done based on a deterministic (most likely) case. The optimum placement of wells within geologic uncertainty is the issue addressed in this paper.

This paper discusses a new approach and workflow process for applying uncertainty analysis using sector model of an undeveloped reservoir and the optimization of development wells under geological uncertainty. Tornado plots were used to identify the highest critical parameters among the list of uncertainties of the field. Experimental Design was used to select simulation runs to build the proxy model. Monte Carlo analysis was then used to generate the density distribution function of cumulative production to identify the P10, P50 & P90 cases. The probabilistic distribution was used to determine the likelihood of the development case under identified risk parameters. Field operation strategies were considered together with optimization of injector-producer spacing, producer-producer spacing, horizontal completion, well length and orientation with geologic uncertainties. The optimized development plan and well placements were used to generate the cumulative production distribution with uncertainty parameters. This workflow was successfully tested in a large carbonate field.

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