The researchers studied clay minerals in sandstone reservoirs in the Xujiahe Formation, Sichuan Basin. They found that chlorite and illite are the main clay minerals, with chlorite positively linked to reservoir porosity and permeability. The iron-magnesium chlorite type, formed in alkaline conditions, lines sandstone grains and does not significantly prevent quartz overgrowth. Chlorite tends to grow in sandbodies with larger pore spaces.