Tight gas reservoirs are often defined as gas-bearing sandstones or carbonates having in-situ permeabilities to gas less than 0.1 mD (Holditch, 2006; Smith et al., 2009). Tight gas reservoir rocks can be at different in-situ physical conditions: deep or shallow; over- or underpressured; high temperature or low temperature; and under different stress states. The reservoir-forming rock can have different textures such as shaley and silty unconsolidated sandstones or clean-cemented sandstones. These different rocks produce gas at low rates. Tight reservoir rocks can be blanket or lenticular, homogeneous or heterogeneous, and can contain a single layer or multiple layers, be fractured or unfractured, and mainly produce dry natural gas.