Characteristics and Weakly Supervised Screening of Diagenetic Facies in the Chang 6 Member, Southwestern Ordos Basin

Linking diagenetic processes to well-log responses is essential for characterizing heterogeneous tight sandstone reservoirs. We integrate petrography, mineralogy, nitrogen adsorption, and conventional logs to investigate the Chang 6 Member, southwestern Ordos Basin. Four dominant-process facies are identified: tightly compacted, siliceous-cemented, clay-filled, and dissolution facies. Dissolution-facies specimens exhibit 87% greater mean nitrogen-accessible mesopore volume than tightly compacted specimens, whereas clay-filled specimens have the highest micropore volume and surface area. Candidate logging associations comprise high density for compaction, low gamma-ray responses and short acoustic transit times for siliceous cementation, elevated gamma-ray and neutron responses with low resistivity for clay filling, and low density with high resistivity for dissolution. Lithological and fluid effects limit the diagnostic specificity of these signatures, requiring integrated interpretation of multiple curves. A weakly supervised workflow enables probabilistic facies screening with uncertain assignments rejected. Independent petrographic validation remains essential because training labels and predictors share log inputs.