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Even though the ensemble Kalman filter (EnKF) is widely used, history matching reservoirs with facies description has proven to be a major challenge. A preferred technique for estimating large scale facies fields within the petroleum industry is still missing. In this paper, we present a new approach to this problem. Instead of applying the EnKF directly to facies realizations, the approach applies a transformation of facies fields to a specific level set function, representing distances between facies types. This ensures better agreement with the EnKF Gaussianity assumptions, and the method always returns facies realizations with geological authenticity. The method also offers large flexibility in generating the initial ensemble, which can be performed using any geostatistical tool. Furthermore, no modifications of the standard EnKF equations are needed.

The methodology is evaluated on two synthetic examples …