Occurrence and origin of pore-lining chlorite and its effectiveness on preserving porosity in sandstone of the middle Yanchang Formation in the southwest Ordos Basin

Abstract The occurrence and origin of pore-lining chlorites in sandstone were studied using mineralogical and crystal chemical analysis and their effectiveness on preserving porosity was discussed. During the sedimentary period of the middle Yanchang Formation, the two provenance and sedimentary systems of the southwest and northeast developed in the southwest Ordos Basin. In the Northeast of the study area, the content of biotite flakes is approximately 10 vol%. Pore-lining chlorites prefer to grow on the surfaces of fine-grained detrital quartz and feldspar but not on ductile grains such as biotite. Pore-lining chlorites that developed during the early stage of eodiagenesis (