Microfacies and Reservoir Space Characteristics of Carbonate Reservoir of the Ordovician Yingshan Formation in Northern Slope of Tazhong Uplift, Tarim Basin

Table 1

Microfacies and sedimentary interpretation of Yingshan Formation.

Code	Microfacies	Description
Mf1	Oolitic grainstone	Grains are ooids of about 0.4 mm in size. The ooids underwent intense alteration, with the internal retained core clearly visible, while the laminated shell underwent dissolution and was filled with calcite (Figure 2(a)).
Mf2	Intraclast grainstone	Grains are mainly sand-sized intraclasts with amounts of algal spherical, which are better sorted and more uniform in size. And a very small amount of fine spherical mortar is filled in the middle (Figure 2(b)).
Mf3	Bioclastic grainstone	Most of grains in the rock are bioclastic with relatively large individuals, and the substrate is a granular colloid of sparry calcite (Figure 2(c)).
Mf4	Bioclastic intraclast grainstone	Internal debris particles range from 0.1 to 0.35 mm, with some grinding rounding, and the particles consist of mud crystal calcite with >70% content (Figure 2(d)).
Mf5	Peloid packstone	Peloids are the most abundant components, generally dominated by bright crystal cementation. The spherical particles are 0.1 mm in diameter, fine and uniform in size, mainly as tiny rounded mud crystal fragments (Figure 2(e)).
Mf6	Bioclastic wackestone	Most grains are silt-sized intraclasts, peloids, and bioclasts, including ostracodes, bryozoans, and algae (Figure 2(f)).
Mf7	Boundstone	Blue algae boundstone, wackestone, and mudstone with a laminar and bounded structure. Fenestral pores are common (Figure 2(g)).
Mf8	Mudstone	The rocks are mainly composed of microcrystalline calcite with a few siliceous particles, thin-bedded structure (Figure 2(h)).
Mf9	Micritic dolostone	This microfacies mainly consists of fine dolomite, basically no internal particles or raw chips inside (Figure 2(i)).