Methods, systems, and apparatuses are disclosed for classifying shale gas formations based on geochemical, petrophysical and/or petrological properties. In preferred embodiments, the methods, systems, and apparatuses classify gas shales according to the processes of hydrocarbon generation (i.e., thermogenic versus biogenic), the degree of clay maturation, the dominant composition of the gas shales, and the like. The methods, systems, and apparatuses also account for formation characteristics such as total organic carbon, degree of Kerogen maturity, and the like. Such an arrangement allows for consistent and reliable identification of productive (and likely profitable) types of shale gas reservoirs.