Diagenesis and division of diagenetic phases of the reservoirs in the North Weifang oil field

The North Weifang oil field is situated in northern Weifang, Shandong. The oil-bearing rock series in the oil field are represented by the Palaeocene-Eocene Kongdian Formation strata. The rock types include the proximal sedimentary rocks such as feldspar sandstone, arkose, lithic sandstone, litharenite, lithic feldspar or feldspar lithic sandstone, lithic feldspathic litharenite. The diagenetic types include compaction, cementation and secondary solution. The reservoir sandstones in the Kongdian Formation went through two diagenetic stages and five diagenetic substages, and six diagenetic phases, of which the slightly compacted and moderately cemented DRF1-type reservoirs have the best reservoir quality, the moderately compacted and highly cemented DRF4-type reservoirs worst; subordinately come the moderately compacted and moderately cemented DRF3-type reservoirs in the Kongdian Formation, intensely compacted and moderately cemented DRF5-type reservoirs in the middle submember of the second member of the Kongdian Formation, and slightly compacted and moderately cemented DRF1-type reservoirs in the lower submember of the first member of the Kongdian Formation.