Impact of Differential Densification on the Pore Structure of Tight Gas Sandstone: Evidence from the Permian Shihezi and Shanxi Formations, Eastern Sulige Gas Field, Ordos Basin, China

Table 4

Typical diagenetic features and evolution sequence for various lithologic modes.

Lithologic mode	Diagenetic features	Diagenetic evolution sequence	Densified time
1	Sandstone rich in plastic rock debris, intensely compaction result in densification	Mechanical compaction (intensely) → densified	Middle of eodiagenesis stage A
2	Sandstone rich in rigid rock debris, intensely compaction result in densification	Mechanical compaction (intensely) → densified	Middle of eodiagenesis stage A
3	Intensely chlorite rim preserve primary pores	Mechanical compaction (weakly) → quartz overgrowth (weakly) → chlorite rim (intensely) → pore development	Middle of eodiagenesis stage A
4	Intensely quartz overgrowth result in densification	Mechanical compaction (weakly) → quartz overgrowth (weakly) → chlorite rim (weakly/undeveloped) → dissolution (weakly, feldspar transformed into kaolinite) → quartz overgrowth (intensely) → densified	Middle of eodiagenesis stage A-later of eodiagenesis stage B
5	Intensely intergrown calcite cementation result in densification	Mechanical compaction (weakly) → quartz overgrowth (weakly) → chlorite rim (weakly/undeveloped) → dissolution (weakly, feldspar transformed into kaolinite) → quartz overgrowth (weakly/undeveloped) → calcite cementation (intensely) → densified	Middle of eodiagenesis stage A-later of eodiagenesis stage B
6	Intensely authigenic quartz result in densification	Mechanical compaction (weakly) → quartz overgrowth (weakly) → chlorite rim (weakly) → dissolution (weakly, feldspar transformed into kaolinite) → quartz overgrowth (undeveloped) → calcite cementation (weakly/undeveloped) → dissolution (weakly, feldspar transformed into kaolinite) → authigenic quartz (intensely) → densified	Later of mesodiagenesis stage A
7	Intensely F-calcite cementation result in densification	Mechanical compaction (weakly) → quartz overgrowth (weakly) → chlorite rim (weakly/undeveloped) → dissolution (weakly, feldspar transformed into kaolinite) → quartz overgrowth (weakly/undeveloped) → calcite cementation (weakly/undeveloped) → dissolution (weakly, feldspar transformed into kaolinite) → authigenic quartz (weakly/undeveloped) → Fe-calcite cementation (intensely) → densified	Middle-later of mesodiagenesis stage B
8	Chlorine rim, dissolution, weakly cementation result in porosity development	Mechanical compaction (weakly) → quartz overgrowth (weakly) → chlorite rim (weakly/undeveloped) → dissolution (weakly, feldspar transformed into kaolinite) → quartz overgrowth (weakly/undeveloped) → calcite cementation (weakly/undeveloped) → dissolution (weakly, feldspar transformed into kaolinite) → authigenic quartz (weakly/undeveloped) → Fe-calcite cementation (weakly) → densified	Middle-later of mesodiagenesis stage B