Diagenetic Facies and Their Controls on the Quality of Tight Sandstone Reservoirs: A Case Study from the Upper Paleozoic Gas Reservoir in the Eastern Ordos Basin, North China

Figure 3

Photomicrographs show lithology characteristics of representative sandstone (plane polarized). (a) Lithic sandstone, showing most altered rock fragments, quartz, and feldspar grains with medium-grained and subangular. (b) Lithic quartz sandstone, showing altered rock fragments and quartz with medium-coarse-grained and subangular. (c) Quartz sandstone, showing quartz grains with medium and coarse grains and subangular.