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Based on an elaboration of the resource potential and annual production of tight sandstone gas and shale gas in the United States and China, this paper reviews the researches on the distribution of tight sandstone gas and shale gas reservoirs, and analyzes the distribution characteristics and genetic types of tight sandstone gas reservoirs. In the United States, the proportion of tight sandstone gas in the total gas production declined from 20%--35% in 2008 to about 8% in 2023, and the shale gas production was 8 310x108 m3 in 2023, about 80% of the total gas production, in contrast to the range of 5%--17% during 2000--2008. In China, the proportion of tight sandstone gas in the total gas production increased from 16% in 2010 to 28% or higher in 2023. China began to produce shale gas in 2012, with the production reaching 250x108 m3 in 2023, about 11% of the total gas production of the country. The distribution of shale gas reservoirs is continuous. According to the fault presence, fault displacement and gas layer thickness, the continuous shale gas reservoirs can be divided into two types: continuity and intermittency. Most previous studies believed that both tight sandstone gas reservoirs and shale gas reservoirs are continuous, but this paper holds that the distribution of tight sandstone gas reservoirs is not continuous. According to the trap types, tight sandstone gas reservoirs can be divided into lithologic, anticlinal, and synclinal reservoirs. The tight sandstone gas is coal-derived in typical basins in China and Egypt, but oil-type gas in typical basins in the United States and Oman. [ABSTRACT FROM AUTHOR]

Exploration and development of large gas fields is an important way for a country to rapidly develop its natural gas industry. From 1991 to 2020, China discovered 68 new large gas fields, boosting its annual gas output to 1 925×108 m³ in 2020, making it the fourth largest gas-producing country in the world. Based on 1696 molecular components and carbon isotopic composition data of alkane gas in 70 large gas fields in China, the characteristics of carbon isotopic composition of alkane gas in large gas fields in China were obtained. The lightest and average values of δ13C1, δ13C2, δ13C3 and δ13C4 become heavier with increasing carbon number, while the heaviest values of δ13C1, δ13C2, δ13C3 and δ13C4 become lighter with increasing carbon number. The δ13C1 values of large gas fields in China range from -71.2‰ to -11.4‰ (specifically, from -71.2‰ to -56.4‰ for bacterial gas, from -54.4‰ to -21.6‰ for oil-related gas, from -49.3‰ to -18.9‰ for coal-derived gas, and from -35.6‰ to -11.4‰ for abiogenic gas). Based on these data, the δ13C1 chart of large gas fields in China was plotted. Moreover, the δ13C1 values of natural gas in China range from -107.1‰ to -8.9‰, specifically, from -107.1‰ to -55.1‰ for bacterial gas, from -54.4‰ to -21.6‰ for oil-related gas, from -49.3‰ to -13.3‰ for coal-derived gas, and from -36.2‰ to -8.9‰ for abiogenic gas. Based on these data, the δ13C1 chart of natural gas in China was plotted. [ABSTRACT FROM AUTHOR]

China has made significant progress in the exploration and development of natural gas in the past 70 years, from the gas-poor country to the world's sixth largest gas production country. In 1949, the annual gas output in China was 1 117×104 m3, the proved gas reserves were 3.85×108 m3, and the average annual gas consumption and available reserves of per person were 0.020 6 m3 and 0.710 7 m3, respectively. By 2018, the average domestic annual gas production per person was 114.857 6 m3 and the reserves were 12 011.08 m3, and the average domestic annual gas production and reserves per person in the past 70 years increased by 5 575 times and 16 900 times, respectively. The exploration and development of large gas fields is the main way to rapidly develop the natural gas industry. 72 large gas fields have been discovered in China so far, mainly distributed in three basins, Sichuan (25), Ordos (13) and Tarim (10). In 2018, the total gas production of the large gas fields in these three basins was 1 039.26×108 m3, accounting for 65% of the total gas production in China. By the end of 2018, the cumulative proved gas reserves of the 72 large gas fields had amounted to 124504×108 m3, accounting for 75% of the total national gas reserves (16.7×1012 m3). New theories of natural gas have promoted the development of China's natural gas industry faster. Since 1979, the new theory of coal-derived gas has boosted the discovery of gas fields mainly from coal-measure source rocks in China. In 2018, the gas production of large coal-derived gas fields in China accounted for 50.93% and 75.47% of the total national gas production and total gas production of large gas fields, respectively. Guided by shale gas theories, shale gas fields such as Fuling, Changning, Weiyuan and Weirong have been discovered. In 2018, the total proved geological reserves of shale gas were 10 455.67× 108 m3, and the annual gas production was 108.8×108 m3, demonstrating a good prospect of shale gas in China. [ABSTRACT FROM AUTHOR]

The natural gas components and geochemistry of 38 ultra-deep gas wells (burial depth greater than 6 000 m) in the Sichuan Basin were analyzed to determine the genesis of ultra-deep natural gas in the basin. The ultra-deep natural gas components of the basin have the following characteristics: Methane has an absolute advantage, which can be up to 99.56% with an average of 86.6%; ethane is low, with an average of 0.13%; there is nearly no propane and butane. So it is dry gas at over-mature thermal stage. The content of H 2 S can be up to 25.21%, with an average of 5.45%. The alkane gas isotopes are: the carbon isotope varies from −32.3‰ to −26.7‰ for methane and from −32.9‰ to −22.1‰ for ethane. There is nearly no carbon isotopic reversal among methane and its homologues. Hydrogen isotope varies from −156‰ to −114‰ for methane, and from −103‰ to −89‰ for some ethane. The carbon isotope of CO 2 varies from −17.2‰ to 1.9‰ and most of them fall within the range of 0±3‰. According to the δ 13 C 1 - δ 13 C 2 - δ 13 C 3 plot, except some wells, all other ultra-deep gas wells are dominated by coal-derived gas. Based on the CO 2 origin distinguishing plot and δ 13 C CO2 , except some individual wells, most of the ultra-deep CO 2 are of carbonate metamorphic origin. H 2 S in the ultra-deep layer of Longgang and Yuanba gas fields belongs to thermochemical sulfate reduction (TSR), while H 2 S from Well Shuangtan belongs to thermal Geochemical characteristics of ultra-deep natural gas in the decomposition of sulfides (TDS). [ABSTRACT FROM AUTHOR]

In order to determine the origin of Carboniferous-Permian (C-P) coal measure gas and Ordovician weathered crust gas, and their gas-filling modes, the chemical and isotopic compositions of the natural gas along with the co-produced groundwater from Paleozoic in the Yanchuannan (YCN) gas field of the Ordos Basin, China, were analyzed. It was found in this work that the gas in the upper gas group of weathered crust (O 1 m 5 1+2 ) reservoirs and the C-P gas had similar δ 13 C 1 and δ 13 C 3 compositions and they were less negative than those of the gas in the lower gas group (O 1 m 5 4 ). While all weathered crust gases had δ 13 C 2 values that are more negative than the C-P gases. The O 1 m 5 4 gas and C-P gas had a very clear boundary in δDCH 4 value, while the O 1 m 5 1+2 gas had the δDCH 4 ranges intersecting with the two others. The C-P gas is inferred derived from coal measures. The O 1 m 5 1+2 gas near erosional valley-form is a mixture of coal-derived gas and marine sapropelic gas, and the remaining Ordovician gases are inferred to originate from marine sapropelic source rock. Both gases were characterized by secondary cracking gas, and thermochemical sulfate reduction (TSR) altered the chemical and isotopic composition of weathered crust gas to a lesser extent due to short TSR reaction time. The changes in water type and total dissolved solids from the Permian to the Ordovician and the D shift phenomenon of O 1 m 5 1+2 water, reveals the fluid vertical migration between the Upper and Lower Paleozoic. Coupled with geological evolution analysis, the ancient erosional valley-form and the surrounding solution cavities and fractures are inferred the main migration channels for coal-derived gas into weathered crust reservoir. Moreover, three vertical gas-filling modes are proposed, i.e., gas seepage in free phase, diffusion phase and water-solution phase, with the importance in descending order. [ABSTRACT FROM AUTHOR]

Abstract: Tight sandstone gas belongs to unconventional natural gas. There is no unanimous agreement about the source of tight sandstone gas source. Both the Yuanba and Tongnanba gas fields in the Sichuan Basin produce tight sandstone gas from Xujiahe Formation gas reservoirs. The geochemical data such as the carbon and helium isotopes of the 14 gas samples from the Xujiahe Formation of 9 wells in the Yuanba gas field show that the gas mainly consists of coal-derived gas from the self-source type, oil-type gas from other source, and a small amount of abiogenic gas, suggesting combination gas sources. The similar geochemical data of 5 gas samples from the Xujiahe Formation of 5 wells in the Tongnanba gas field indicate that the gas consists of oil-type gas from other source, accompanied by a small amount of abiogenic gas, also being of mixed origins. Therefore the Xujiahe Formation tight sandstone gases of the Yuanba and Tongnanba gas fields do not come from coal measure alone. They have a variety of sources, mainly the coal-derived gas or oil-type gas of organic origin or the mixture of them. [Copyright &y& Elsevier]

Abstract: To investigate the ability of exogenous bacteria to degrade brown coal, methanogens were enriched from anaerobic sludge and domesticated using brown coal as carbon source. After domestication, the lag time of initial gas production is shortened from 12 to 6 days and the CH4 production increased by 29.2% in 30 days. The generated biogas is composed of CH4 and a little CO2, no heavy hydrocarbons are detected. Experiments on gas production influencing factors demonstrate that the best initial pH for the culture medium is 7.0 and the maximum gas production is 1.9 times and 2.4 times higher than that at pH 6.4 and pH 7.4, respectively. The particle size of coal is one of factors influencing the gas production: the general trend is the smaller the particle size, the bigger the gas production, but the variation of gas production is not significant with decreasing particle size. Gas produced by the culture medium accounts for around 50% of the total gas production and it is likely caused by the addition of L-cysteine (0.5 g/L) and yeast extract (1 g/L) to the medium. [Copyright &y& Elsevier]

Abstract: Tight gas reservoirs refer to the tight sandstone fields or traps accumulating natural gas of commercial values. According to reservoir characteristics, reserves, and structural height, they can be divided into two types, continuous-type and trap-type: the former are located at the lower part of the structure and have indistinct trap boundaries, inconsistent gas-water boundaries and reversal of gas and water, and their reservoirs are the same as or near the source; the latter are located at the higher part of the structure, with gas above water in traps, low reserves, and relatively high production. Tight gas in China is all coal-derived, dominantly alkane gases (C1–4), in which the amount of methane is greatest and the alkane gases have positive carbon isotopic series. The content of non-hydrocarbon gases (mainly CO2 and N2) is low. At the end of 2010, the reserves and annual production of tight gas in China accounted for 39.2% and 24.6% of the total natural gas, respectively, and the proportions are expected to increase. Compared to the shale gas and coalbed gas, tight gas should be considered in priority in the exploration and exploitation of unconventional gas in China. [Copyright &y& Elsevier]

Abstract: Hydrocarbon-generation kinetics is of applicable significance in the study of coal-derived gas pool formation. Its research progress in recent years includes: in combination with geothermal history, it is used as a tool to evaluate source rocks dynamically and depict the change of source kitchen with geological time; according to the carbon isotope fractionation kinetics, a more precise model of identifying coal-derived gas is developed, which contains the kinetic relationship among gas compounds; the combination of compositional kinetics and carbon isotopic kinetics leads to the study method of accumulation processes of coal-derived gases, which is constrained precisely by multi kinetic indices; with the reservoir records, generation kinetics is used to study the whole gas life including generation, charge and alteration. The problems that need investigation are generation kinetics of coal-derived gas at low maturity, pressure effects on gas generation, minerals and water influences, and kinetics of residual soluble organic matter at high maturity. [Copyright &y& Elsevier]

Abstract: Since its formation in China 30 years ago, the theory of coal-derived gas has not only opened a new field of coal-derived gas exploration, but also increased the proved reserves of coal-derived gas from 1/10 to 7/10 in the total gas of China; the nation''s proved gas reserves rise sharply from 2 264×108 m3 to 6.4×1012 m3; the annual production of gas rises from 137.34×108 m3 to 760×108 m3; and the nation''s coal-derived gas fields (reservoirs) increases from less than 10 (excluding Taiwan) to 124. After briefing the major developments of China''s coal-derived gas exploration, this paper concentrates on the exploration development of coal-derived gas in Ordos Basin, Tarim Basin and Sichuan Basin where large numbers of coal-derived gas fields have been discovered. With carbon isotopic data of alkane gases, it also demonstrates that some gas fields of controversial origin (Jingbian, Kekeya and Akemomu gas fields) are of, or predominantly of, coal-derived gas, and that a few gas reservoirs (Wolonghe, Naxi, Hejiang gas fields) in the Xujiahe Formation coals of Sichuan Basin are oil-associated gas. [Copyright &y& Elsevier]