<![CDATA[In the East Java Basin Indonesia, the Ngrayong Sandstone has been targeted as a reservoir for carbon capture and storage (CCS). In this CCS system, the limestone and mudstone of Bulu and Wonocolo Formation is expected to serve as the primary seal. The purpose of this study are to investigate the lithological, mineralogical, and mechanical and petrophysical properties of the Ngrayong, Bulu and Wonocolo Formations from surface lithology as an analogue study, and later will be adapted to subsurface injection well (Jepon-1) to characterize its potential as a functional reservoir and seal in a CCS system. Two Shallow core-drilling and outcrop sampling derived Ngrayong, Bulu and Wonocolo Formation samples are described using a combination of petrography, x-ray diffraction, petrophysical and mechanical properties analyses. These analysis show that the Ngrayong, Bulu and Wonocolo Formation contains seven different lithofacies (claystone with thin quartz sandstone, clean quartz sandstone, mudstone, bioclistic limestone, calcarenitic limestone, sandy marl, and grainstone) with fine-scale heterogeneities in fabric and mineralogy that greatly influence the petrophysical properties. Porosity, permeability, and other petrophysical properties suggest that have the capability to serve as a suitable CCS seal. Abundant authigenic minerals and dissolution textures indicate that multiple generations of past fluid-rock interactions have occurred within the Ngrayong, Bulu and Wonocolo Formation. Minerals that would be potentially reactive in a CCS system (including carbonate and chlorite) are common in the Ngrayong and Wonocolo Formation]]>
