Series of cementitious binders with potential application in oil and geothermal wells were developed.Commercial G-oil cement modified by adding blast furnace slag and silica fume, fiber-reinforced cement composites with various content of High Alumina Cements (HAC), Portland cement, and Poly-sodium phosphate were used as binder composites to prepare slurries that were submitted to hydrothermal curing in autoclave up to 7 days (163 hours) at different regimes of temperatures and vapor pressures.Pore structure parameters, microstructure and hydrated products were evaluated after 7 days curing by using the TGA/DSC,MIP, XRD and SEM.