Natural-gas processing at ambient conditions (i.e., pentane and heavier) are called "natural-gas condensate" (sometimes also called "natural gasoline" or simply "condensate"). Natural gas is called "sweet gas" when relatively free of hydrogen sulfide; gas that does contain hydrogen sulfide is called "sour gas". Natural gas, or any other gas mixture, containing significant quantities of hydrogen sulfide, carbon dioxide or similar acidic gases, is called "acid gas." Raw natural gas can also come from methane deposits in the pores of coal seams, and especially in a more concentrated state of adsorption onto the surface of the coal itself. Such gas is referred to
Natural gas called retrograde condensation. The liquid thus formed may get trapped as the pores of the gas reservoir get depleted. One method to deal with this problem is to re-inject dried gas free of condensate to maintain the underground pressure and to allow re-evaporation and extraction of condensates. More frequently, the liquid condenses at the surface, and one of the tasks of the gas plant is to collect this condensate. The resulting liquid is called natural gas liquid (NGL) and has commercial value. Shale gas is natural gas produced from shale. Because shale has matrix permeability too low to allow gas