1. A computer-implemented method for approximating multiphase flow reservoir production simulation, the method comprising: generating a set of pseudo-phase production relative permeability curves; receiving production rate history data; receiving simulation configuration parameters; performing flow simulation using the set of pseudo-phase production relative permeability curves determining an optimal matching pseudo-phase production simulation result that best matches the production rate history data; and performing relative permeability inversion using signal processing analysis of production rate history data to approximate relative permeability curves with quantified uncertainty.