Genesis and distribution of natural gas in the foreland basins of China

This article discusses the geochemical characteristics of various types of natural gas and features of gas reservoirs in the foreland basins in China. We conclude that there are four types of natural gas in origin: coal-formed cracking gas, coal-formed thermal gas, oil-type thermal gas and mixed gas. Coal-formed gases are generated from three sets of coal measures: Permo-Carboniferous Formations in the Ordos Basin, Upper Triassic Formations in the Qaidam Basin, and Triassic Formations in northwest China. Source rocks for the oil-type gas include Permian Formations in the Junggar Basin, Triassic Formations in the Qaidam Basin, and lacustrine source rocks in basins along the Hexi Corridor. Abnormally high pressures commonly exist in the gas reservoirs in foreland basins where multiple sets of source–reservoir–seal combinations are present, and the major trap type is the anticlinal trap type and faults are the major hydrocarbon migration pathways.