This paper presents the initial database of the mineralogy of the caprock and reservoir sandstones of the Heletz field scale experimental CO2 injection site, Israel. The XRD mineralogy results show that the Heletz caprock has K-feldspar as the primary mineral (40%) followed by kaolinite (15%) and plagioclase feldspar (12%) then illite (6%) and muscovite (6%) with minor quartz, calcite, pyrite, chlorite and ankerite with traces of siderite. The Heletz reservoir rock is primarily quartz (70%) followed by K-feldspar (12%) and plagioclase feldspar (4%) with minor illite, kaolinite, muscovite, chlorite ankerite and pyrite with traces of dolomite, calcite and siderite. “Cook and look” bench experiments were conducted on the Heletz caprock and reservoir sandstone samples to identify if there was any immediate mineral reactivity that would influence permeability on exposure to CO2 that may cause concerns during well completion and initial injection of CO2 at Heletz. The sandstone exhibited reactivity under brine dis-equilibrium which was observed in the field with loss of injectivity which was restored by injecting KCL into the well and performing 20 swab-suctions. The caprock revealed no reactivity of immediate concern to the well completion and injection strategy and will retain its integrity.