The origin and evolution of thermogenic gases in organic-rich marine shales

Sustainable thermogenic CH4 and H2 generation in the Nankai Trough subduction zone

“…Hence, from the viewpoint of thermal decomposition, the thermogenic CH 4 generation is regarded as proceeding almost in a closed system. In closed-system pyrolysis experiments of sedimentary organic matter, the thermogenic CH 4 concentration gradually increases with increasing thermal maturation from VR = 0.7 to 4.0%, and C 2 H 6 disappears at around VR = 2.5% (Behar et al, 1997;Xiong et al, 2016). These relationships between the concentration changes in thermogenic CH 4 and C 2 H 6 and VR values are consistent with the maturation stages (VR values) of the residual CH 4 and C 2 H 6 concentration changes in the old accretionary prisms (Fig.…”

“…Although the sediments in the subduction zone comprise some terrestrial organic matter, we assumed the same Type II (marine) kerogen and TOC concentration (0.5 wt%) for comparison convenience. According to pyrolysis experiments of kerogen in a closed system, the ultimate yield of CH 4 from Type II kerogen was approximately 300 mgCH 4 /gTOC (Behar et al, 1995;Xiong et al, 2016). Therefore, the annual generation rate of CH 4 can be estimated from the TOC concentration, the apparent sediment density (2.6), and the movement velocity of the underthrust sediments and the accretionary prisms.…”

From Micropores to Macropores: Investigating Pore Characteristics of Longmaxi Shale in the Sichuan Basin

“…7 Shale gas is generated during the different stages of organic maturation, which includes biogenetic gas, thermogenic gas, and pyrolysis genetic gas. 8,9 The principal component of shale gas, methane, predominantly resides in the form of adsorbed gas, adhering to the surfaces of organic pores and clay minerals, or as compressed gas within intergranular pores and fractures, with a lesser quantity existing as dissolved gas within oil and water. 10,11 In some cases, the adsorbed gas contributes up to 50−60% of the gas in place (GIP), which is constituted by the sum of adsorbed gas, free gas, and dissolved gas.…”

“…These factors collectively contribute to the development and characteristics of the pores within shale formations. , Due to different sedimentology, variant diagenetic processes, and multistage tectonism, shale formations have a complex pore system with micropores (with diameter <2 nm), mesopores (2–50 nm in diameter), and macropores (with diameter >50 nm), according to the International Union of Pure and Applied Chemistry (IUPAC) classification . Shale gas is generated during the different stages of organic maturation, which includes biogenetic gas, thermogenic gas, and pyrolysis genetic gas. , The principal component of shale gas, methane, predominantly resides in the form of adsorbed gas, adhering to the surfaces of organic pores and clay minerals, or as compressed gas within intergranular pores and fractures, with a lesser quantity existing as dissolved gas within oil and water. , In some cases, the adsorbed gas contributes up to 50–60% of the gas in place (GIP), which is constituted by the sum of adsorbed gas, free gas, and dissolved gas . Hence, the pores are the dominate sites for gas generation and storage.…”