The alteration of wettability can be a key mechanism for additional oil production from hydrocarbon reservoirs worldwide. This paper models thermally-induced wettability alteration from hot-water imbibition in naturally fractured reservoirs (NFRs). Hot-water (or steam) enhanced oil recovery (EOR) in fractured reservoirs can lead to increased oil recovery by enhancing water imbibition into matrix blocks, rendering the formation more water-wet. This will increase recovery as a result of decreased oil-water interfacial tension and reduced residual oil saturation. Modeling and evaluating production mechanisms in such a process in NFRs requires an understanding of multiphase flow parameters. In this work, numerical simulation codes with finite-difference formulations were developed to couple fluid flow and heat transfer for 1D and 2D flow geometries in spontaneous imbibition. This paper examines the effect of elevated temperature on wettability by considering various initial and boundary conditions. This approach results in more accurate simulation results as the relative permeability and capillary pressure curves are updated at each time step and for each grid (or each rock-type). The results from this study confirmed: a) the rate of recovery in co-current is generally higher than that in counter-current imbibition in a hot-water imbibition process, b) changing the wetting state in matrix from intermediate-or oil-wet to more water-wet proved to increase the ultimate recovery by reducing the residual oil saturation, c) updating the k(r) and P-c curves vs. temperature in simulating a hot-water injection process in NFRs can be more accurate than the commercial simulators where the relative permeability and capillary pressure curves are updated based on solely their end-points. (C) 2017 Elsevier Ltd. All rights reserved.