Large-scale tight sandstone oil and gas reservoirs in China's Ordos Basin have varying quality due to different sediment types and processes. The Shanxi Formation in the basin is mainly delta and lake sediments. Diagenesis, or rock changes over time, affected the reservoirs, with compaction and cementation reducing properties, while dissolution improved them. The best reservoir properties are found in distributary channels, underwater channels, and mouth bars, while natural levees have the lowest quality.