The evolution of water-injector injectivity is a complex phenomenon because of the opposite effects induced by thermal fracturing and formation damage. A numerical model HydFrac, based on a two-phase thermal reservoir simulator including descriptions of fracture mechanics and formation plugging by injected particles, is first presented. Special attention is paid to the analysis of fracture closure rate during injection shut-in and to the description of formation damage. The results show the importance of injection duration on fracture closure rate during shut-in. On the other hand, a case including a first step of clean water injection and a second step of produced water re-injection is presented. The obtained results indicate a stabilization of fracture length at the end of clean water injection followed by a rapid increase during produced water re-injection. The evolution of the effective fracture width is analyzed to indicate the start of fracture filling by particles.