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Tight sandstone gas from coal-measure source rock is widespread in China, and it is represented by the Xujiahe Formation of the Sichuan Basin and the Upper Paleozoic of the Ordos Basin. It is affected by planar evaporative hydrocarbon expulsion of coal-measure source rock and the gentle structural background; hydrodynamics and buoyancy play a limited role in the gas migration-accumulation in tight sandstone. Under the conditions of low permeability and speed, non-Darcy flow is quite apparent, it gives rise to gas-water mixed gas zone. In the gas displacing water experiment, the shape of percolation flow curve is mainly influenced by core permeability. The lower the permeability, the higher the starting pressure gradient as well as the more evident the non-Darcy phenomenon will be. In the gas displacing water experiment of tight sandstone, the maximum gas saturation of the core is generally less than 50% (ranging from 30% to 40% and averaging at 38%); it is similar to the actual gas saturation of the gas zone in the subsurface core. The gas saturation and permeability of the core have a logarithm correlation with a correlation coefficient of 0.8915. In the single-phase flow of tight sandstone gas, low-velocity non-Darcy percolation is apparent; the initial flow velocity (Vd) exists due to the slippage effect of gas flow. The shape of percolation flow curve of a single-phase gas is primarily controlled by core permeability and confining pressure; the lower the permeability or the higher the confining pressure, the higher the starting pressure (0.02–0.08 MPa/cm), whereas, the higher the quasi-initial flow speed, the longer the nonlinear section and the more obvious the non-Darcy flow will be. The tight sandstone gas seepage mechanism study shows that the lower the reservoir permeability, the higher the starting pressure and the slower the flow velocity will be, this results in the low efficiency of natural gas migration and accumulation as well as low gas saturation. The laboratory modeling on gas migration accumulation mechanism in coal-measure tight sandstone can provide a theoretic foundation to reveal the tight sandstone gas enrichment regularity, evaluation of prospecting area, and the study of development mechanism.

The geochemical characteristics, origin, and source of natural gas in the Dongping–Niudong areas are researched based on the information of components and the stable carbon isotopes of natural gas. The main component of hydrocarbon gas is methane, and C2+ possesses a relatively low content that ranges from 0.5% to 6.5%. The dryness coefficient of the Dongping area is more than 0.97, which categorizes as dry gas. The dryness coefficient of the Niudong area ranges from 90.3% to 98.1%, whilst having the characteristics of dry gas coexisting with wet gas. The δ13C1 dryness coefficient varies from −17.58‰ to −36.4‰, and δ13C2 is greater than −29‰. The gas of the Dongping 3 block has the characteristics of an abiogenic gas such as the reversed carbon isotope series. The combination of the relationship between the component of CO2 and δCCO213 and the background of development of hydrocarbon-generating sag, suggests that it is coal-derived gas. The RO and fluid inclusion studies show that the gas in Niudong area is mainly derived from Early Jurassic coal-measure source rocks of Kunteyi Sag, and there are two periods of hydrocarbon fillings. The first filling is mainly oil, and the second is mainly high mature gas; gas in Dongping area is mainly derived from Early Jurassic coal-measure source rocks of Pingdong–Yiliping Sag, and there are four periods of high-over mature gas fillings. The phenomenon of reversed carbon isotope series in Dongping area resulted from the multiple gas charging.

The coal measure gas sources of coal-derived gas fields in the Late Paleozoic China are the Lower Carboniferous Dishuiquan Formation, the Upper Carboniferous Batamayineishan Formation and Benxi Formation, the Lower Permian Taiyuan Formation and Shanxi Formation, and the Upper Permian Longtan Formation. The coal-derived gas accumulates in Ordovician, Carboniferous, Permian, and Paleocene reservoirs and are distributed in Ordos Basin, Bohai Bay Basin, Junggar Basin, and Sichuan Basin. There are 16 gas fields and 12 of them are large gas fields such as the Sulige large gas field which is China's largest reserve with the highest annual output. According to component and alkane carbon isotope data of 99 gas samples, they are distinguished to be coal-derived gas from coal-derived gas with δ13C2 > −28.5‰ and δ13C1 -δ13C2 -δ13C3 identification chart. The Late Paleozoic relative gas fields of coal measure are significant for the Chinese natural gas industry: proven natural gas geological reserves and annual output of them account for 1/3 in China, and the gas source of three significant large gas fields is coal-derived, which of five significant large gas fields supporting China to be a great gas producing country. The average reserves of the gas fields and the large gas fields formed from the late Paleozoic coal measure are 5.3 and 1.7 times that of the gas fields and the large gas fields in China.

The carbon isotopic series of alkane gases were divided into three types: (1) positive carbon isotopic series: δ 13 C values increased with increasing carbon numbers among the C 1 –C 4 alkanes, which is a typical characteristic for primary alkane gases; (2) negative carbon isotopic series: δ 13 C values decreased with increasing carbon numbers among the C 1 –C 4 alkanes; and (3) partial carbon isotopic reversal, which had no increasing or decreasing relationship between the δ 13 C values and carbon numbers. Negative carbon isotopic series were further divided into primary and secondary origins. The primary is a typical characteristic of abiogenic gases, while the secondary is a result of the secondary alteration imposed on biogenic gases usually observed in over-mature shale gas and coal-derived gas. Previous research has proposed several possible explanations for negative carbon isotopic series of secondary origin, such as secondary cracking, diffusion, and the Rayleigh fractionation of ethane and propane through redox reaction with the participation of transition metal and water at 250–300 °C. After a comparative study, the authors found that the negative carbon isotopic series of secondary origin for both shale gas and coal-derived gas appeared in areas where source rocks (shales) were at an over-mature stage, but not in areas where source rocks (shales) were only at a high-maturity stage. As a result, high maturity (>200 °C) was the main controlling factor for the occurrence of negative carbon isotopic series of secondary origin in thermogenic gases. Within this maturity interval, secondary cracking, diffusion, and Rayleigh fractionation of ethane and propane could happen separately or together.