(adj). Geology, Shale Gas. Possessing the quality of variation in rock properties with location in areservoir or formation. Shale gas reservoirs are heterogeneous formations whose mineralogy, organic content, natural fractures, and other properties vary from place to place. This heterogeneity makes petroleum systemmodeling, formation evaluation, and reservoir simulation critical to maximizing production from shale reservoirs. Ant: Homogeneous. See: Heterogeneity, Anisotropic, Isotropic