A New Parameterization Technique for the Calibration of Facies Proportions in History–matching Processes

In this paper, we propose a parameterization technique to automatically adjust facies proportions in a history-matching process. Facies proportions being usually non stationary, they involve a number of parameters proportional to the number of grid blocks which can not be handled in practice. Our technique allows us to vary facies proportions from a reduced number of parameters. This method depends on the ratio of average proportions between facies groups with a priori poorly known proportions. The changes in the ratio values are driven by the optimization process and induce variations in facies proportions over the target area. Two different algorithms are introduced depending on the geological environment. The simplest and most efficient one generates discontinuity between the target area and the embedding environment while the second one ensures continuity. One advantage of both techniques is that they do not depend on the stochastic method used to simulate the facies realizations. To stress the potential of this approach, we recap the results obtained for a faulted turbidite field located in offshore Angola and show how this technique helped to improve the calibration of 4D seismic data.