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

Abstract

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 CO2sequestration. 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 highQincreases with increasing CO2pressure, in contrast with the low-Qbehaviour where the intensity decreases with increasing pressure. Data treatment for high-Qscattering at different pressures of CO2is also introduced to explain this anomalous behaviour. The analysis shows that a significant proportion of the pore system consists of micropores (<20 Å) and that the majority (80%) of these micropores remain inaccessible to CO2at reservoir pressures.