Geologists are increasingly realizing the unique perspective that neutron scattering offersforunlocking the complex geologic histories of rocks. In this study, we propose to answerthequestions: What controls the formation and evolution of sub-micrometer porosity withincarbonatereservoirs? and Which of these pores are physically accessible to reservoir fluids (i.e.,water or hydrocarbons)? We will combine contrast-matching SANS to assess the sub-micrometerpore size distribution within carbonate reservoir sample and describe which of these pores areaccessible to contrast-matched fluids. From these results, we will begin to develop acategorization of where sub-micrometer porosity will exist within carbonate reservoirs, and therebygain a better understanding of the utility of particular formations for various uses.