Quantifying the effect of chlorite on reservoir quality and CO2 sequestration in deep saline aquifers from the permian tight sandstone reservoir in the ordos basin, China

Chlorite can strongly affect the quality of clastic sandstone reservoirs and may also impact the potential of geologic sequestration of CO₂ in deep saline aquifers. However, there is a lack of quantitative evaluation of the effect of chlorite on CO₂ sequestration in sandstones to date. Here we applied a suite of analytical techniques including petrographic and petrological analysis, X-ray diffraction measurement, petrophysical analysis, and CO₂-fluid-rock reactive-transport simulations to investigate the impact of chlorite on both reservoir quality and CO₂ geological sequestration in the Upper Permian sandstones in the northeastern Ordos Basin, China. Three types of chlorite are present in the reservoir sandstone: grain-coating, pore-throat-blocking, and pore-filling. Grain-coating chlorite sandstones feature thin chlorite wrapping on sand grain surfaces that effectively prevent quartz cementation, thus preserving good reservoir porosity and permeability. Pore-throat-blocking chlorite sandstones generally exhibit high porosity but low permeability with the thick chlorite coatings inhibiting quartz cement growth and preserving porosity while blocking pore throats and reducing permeability. Pore-filling chlorite sandstones are characterized by both low porosity and low permeability due to extensive chlorite filling of the pore spaces as matrix. Reactive transport simulations demonstrate that high-porosity and -permeability reservoir sandstones may not always be the most favorable sandstone type for CO₂ geological sequestration when considering the key geochemical sequestration mechanisms (i.e. dissolution and mineral trapping). When disregarding the impact of chlorite on reservoir quality, pore-filling chlorite sandstones, with their high chlorite content, are most suitable for CO₂ sequestration due to their greater capacity for trapping CO₂ via mineralization. However, when both chlorite abundance and reservoir quality factors are considered, pore-throat-blocking chlorite sandstones would possess the largest total CO₂ sequestration capacity.