Determination of closed porosity in rocks by small-angle neutron scattering

Small‐angle neutron scattering (SANS) and ultra‐small‐angle neutron scattering (USANS) have been used to study a carbonate rock from a deep saline aquifer that is a potential candidate as a storage reservoir for CO2 sequestration. A new methodology is developed for estimating the fraction of accessible and inaccessible pore volume using SANS/USANS measurements. This method does not require the achievement of zero average contrast for the calculation of accessible and inaccessible pore volume fraction. The scattering intensity at high Q increases with increasing CO2 pressure, in contrast with the low‐Q behaviour where the intensity decreases with increasing pressure. Data treatment for high‐Q scattering at different pressures of CO2 is also introduced to explain this anomalous behaviour. The analysis shows that a significant proportion of the pore system consists of micropores (