Distribution and Geochemical Characteristics of Hydrogen in Natural Gas from the Jiyang Depression, Eastern China

Abstract

Hydrogen gas accelerates hydrocarbon generation, but little is known about its distribution and origin in petroliferous basins, which has hindered the further exploration. Taken the Jiyang Depression in eastern China as an example, this study collected natural gas from different tectonic units, and analyzed various geochemical characters including gas contents, and carbon and hydrogen isotopic composition. The result shows that: (1) hydrogen gas is widespread distributed, but its content is very low, which typically ranges from 0.01% to 0.1% in this region; (2) the ratios of H2/3He, indicative of the origins of hydrogen gas, suggest that mantle‐derived hydrogen is dominant. Even in tectonically stable areas absent with deep fluid activities, there is also mantle‐derived; (3) the isotopic composition of hydrogen falls in the range of −798‰ to −628‰ (relative to VSMOW standard). In areas with deep‐derived fluids, the hydrogen gas has a similar isotopic composition with the previously documented deep‐sourced gas, with lighter isotopic composition. In contrast, hydrogen gas has a heavier isotopic composition in relatively stable areas. The isotopic signatures suggest that there is a mixture of mantle‐ and crust‐derived hydrogen gas in the relatively stable area, which is consistent with the H2/3He ratios. Therefore, it is clear that the hydrogen gas has a much wider distribution than found in the deep‐derived fluid area, resulting in a much broader area with hydrogenating effect for resource rock. This understanding will provide new insights for hydrocarbon generation research and resource assessment in petroliferous basins.

Catalytic Hydrogenation of Post-Mature Hydrocarbon Source Rocks Under Deep-Derived Fluids: An Example of Early Cambrian Yurtus Formation, Tarim Basin, NW China

“…Mango et al ( , 1997 showed in an open system that the reaction of exogenous hydrogen with organic matter promotes the rate of HC generation under the action of transition metals. Meng et al (2015) confirmed that deep hydrogenrich fluids can activate and increase the HC regeneration of ancient source rocks through experiments. Liu et al (2016) showed that there is Fischer-Tropsch-type (FTT) interaction between H 2 and CO 2 produced by the thermal alteration of source rocks in the geological environment to synthesize HCs.…”

“…A large amount of gas components carried by the deep-derived fluids contain volatile materials, such as H 2 , CH 4 , H 2 S, CO 2 , N 2 , and He. As one of the main volatile fluids, the distribution of geologic H 2 (molecular hydrogen) is widespread in ocean ridges, active tectonic belts, and the Precambrian or Cenozoic strata distributed on land (Jeffrey and Kaplan, 1998;Allen and Seyfried, 2004;Newell et al, 2007;Tivey, 2007;Bradley and Summons, 2010;Sherwood-Lollar et al, 2014;Meng et al, 2015;Etiope, 2017;Guélard et al, 2017;Etiope and Whiticar, 2019;Bougault et al, 2019;Klein et al, 2019;Klein et al, 2020). H 2 has a variety of genetic types, including the release of deep magma degassing, the serpentinization of ultrabasic-basic rocks (Sherwood-Lollar et al, 2014;Etiope, 2017;Klein et al, 2019;Klein et al, 2020), radiolysis of water due to the presence of radioactive minerals (Sherwood-Lollar et al, 2014;Milesi et al, 2016), mechanical cracking of Si-bearing rock (Hirose et al, 2011;Telling et al, 2015), and the reduction of organic matter by microorganisms (Shuai, et al, 2010).…”

“…These deep-derived fluids can hydrogenate post-mature kerogen, thereby activating kerogen's ability to regenerate HCs, by activating the original inert carbon in kerogen and generating HCs (Meng et al, 2015). The post-mature kerogen is rich in polycyclic aromatic HC compounds and polymer groups and has a low H/C ratio.…”

Effects of Deep Fluids on Hydrocarbon Generation and Accumulation in Chinese Petroliferous Basins

“…Many Chinese basins, such as the Songliao (Guo Qingwu, 2004) and Bohai Bay (Meng Qingqiang, 2011) Basins in eastern China, the Sichuan (Zhang Shuichang et al, 2007;Xiao Zhihua et al, 2008) and Ordos (Liu et al, 2009) Basins in central-western China, and the Tengchong Basin (Shangguan Zhiguan and Huo Weiguo, 2002) in the southern China, all contain H 2 (Table 1). Usually, the H 2 concentration is low and varies in a large range from 0.01% (Meng Qingqiang, 2011;Meng Qingqiang et al, 2015) to 5.2% (Shangguan Zhiguan and Huo Weiguo, 2002).…”

Geochemical Characteristics and Genetic Types of Natural Gas in the Xinchang Gas Field, Sichuan Basin, SW China

“…Natural gas is generally dominated by gaseous alkanes with relatively simple chemical compositions compared to crude oil. The geochemical characteristics of natural gas, such as chemical composition, carbon and hydrogen isotopic composition, as well as noble gas isotopic composition are fundamental for the study of the origin, migration, accumulation and alteration of natural gas, and have played an important role in revealing the organic type, thermal evolution degree and sedimentary environment of natural gas source rocks (Stahl, 1977;Schoell, 1980;Chung et al, 1988;Prinzhofer and Huc, 1995;Rooney et al, 1995;Whiticar, 1999;Tang et al, 2000;Zhang Xiaobao et al, 2003;Dai et al, 2004;Zhu Guangyou et al, 2007;Liu Quanyou et al, 2011;Ni et al, 2011;Liu et al, 2014a;Meng et al, 2015;Tao Cheng et al, 2015;Fu Xiaofei et al, 2016;Liu et al, 2016;Ma Yongsheng and Zhao Peirong, 2016).…”