A model for two-phase, incompressible, immiscible fluid flow in a highly fractured porous medium is derived as a simplification of a much more detailed dual-porosity model. This simplified model has a nonlinear matrix-fracture interaction, and it is more general than similar existing "transfer function" models. It is computationally less complex than the detailed model, and simulation results are presented which assess any loss in accuracy. It is shown that the new model approximates capillary effects quite well, and better than similar existing models.