The Evolution of Diagenetic Fluids and Accumulation Characteristics of Tight Sandstone Reservoir in Upper Paleozoic, Southwestern Ordos Basin

Figure 3

The typical diagenetic characteristics of sandstone reservoirs under microscope in the southwestern Ordos Basin. (a) Oriented mica and clastic particles and primary pores, Qingshen 2 well, Shan 1 section, 4733 m, (-); (b) bending deformation of clay minerals, Zitan 1 well, He 8 section, 3740.51 m, (+); (c) linear contact and concave-convex contacts between particles, He 3 well, Shan 1 section, 4146.16 m, (+); (d) concave-convex contacts of particles, He 3 well, He 8 section, 4079.88 m, (+); (e) quartz overgrowths and siliceous cements, Qingtan 2 well, Shan 1 section, 4705.68 m, (+); (f) authigenic quartz microcrystal, Zhentan 1 well, Shan 1 section, 4381.13 m, (-); (g) scaly illite aggregates filling intergranular pores, Qingshen 2 well, Shan 1 section, microscope; (h) flaky illite filling intergranular pores, Qingshen 2 well, Shan 1 section, SEM; (i) kaolinite microcrystalline aggregates filling pores, preserving morphology of feldspar and other clastic particle. Zhentan 1 well, Shan 1 section, microscope; (j) vermicular kaolinite filling intergranular pores, Zhentan1 well, Shan 1 section, SEM; (k) calcite cement, Ling 1 well, Shan 1 section, 3698.60 m, (+); (l) micrite calcite cement, He 3 well, Xiashihezi section, 4081.68 m, (+); (m) feldspar metasomatized by micrite with remnant twining, Zhentan 1 well, Shan 1 section, 4379.07 m, (+); (n) metasomatic micrite and clay minerals with the morphology of lithic particles, Lian 1 well, Shan 1 section, 3469.69 m, (+); (o) quartz metasomatized by sparry calcite cement, He 3 well, Shan 1 section, 4146.62 m (+); (p) lithic particles metasomatized by flaky illite, He 3 well, Shan 1 section, 4146.62 m (+); (q) kaolinite altered from volcanic materials (K) and illite (Y), Lian 1 well, Shan 1 section, 3470.03 m, (-); (r) kaolinization altered from volcanic materials, He 3 well, Shan 1 section, 4146.23 m, (-); (s) dissolution pores of the clay and calcareous cements, Zhentan 1 well, Shan 1 section, 4387.7 m; (t) dissolution pores of cement, Chuntan 1 well, He 8 section, 1723.73 m. All photomicrographs were under microscope unless otherwise specified. Mineral abbreviations: Y: foliated illite; Yi: scaly illite; Ca: calcite cement; K: volcanic material.

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