Geologists are increasingly realizing the unique perspective that neutron scattering offers for unlocking the complex geologic histories of rocks. In this study, we propose to answer the question: What controls the formation and evolution of sub-micrometer porosity within carbonate reservoirs? We will use SANS to systematically assess the sub-micrometer pore size distribution within carbonate reservoir samples formed in a variety of depositional environments and subjected to a range of chemical and temperature/pressure histories in order to categorize the geologic regimes that give rise to individual porosity types. From these porosity classifications, we can then begin to develop a predictive capacity for where sub-micrometer porosity will exist within carbonate reservoirs, and thereby gain a better understanding of the utility of particular formations for various uses.