Estimation of relative permeability and capillary pressure for tight formations by assimilating field production data

A novel EnKF technique together with its detailed workflow has been developed and successfully applied to simultaneously evaluate relative permeability and capillary pressure for tight formations by history matching the field production data. The power-law model is firstly used to represent the relative permeability and capillary pressure curves, while its parameters are tuned automatically and finally determined once the production data have been assimilated completely. This technique has been validated by using a synthetic 2D reservoir model with two scenarios, where two-phase and three-phase relative permeabilities together with capillary pressure curves are evaluated, respectively. The estimated relative permeability and capillary pressure have been found to improve progressively and their corresponding uncertainties are mitigated gradually as more production data are assimilated. Finally, there exists an excellent agreement between both the updated relative permeability and capillary pressure curves and their corresponding reference curves, leading to excellent history matching results. As such, the uncertainties associated with both the updated relative permeability and capillary pressure curves and the updated production profiles are reduced significantly. The capillary pressure cannot be determined as accurately as the relative permeability due to its less sensitivity to the production data.