Hindawi Geofluids Volume 2021, Article ID 6674815, 12 pages https://doi.org/10.1155/2021/6674815 Research Article Characteristics and Origin of Methane Adsorption Capacity of Marine, Transitional, and Lacustrine Shales in Sichuan Basin, China Xianglu Tang ,1 Wei Wu,2 Guanghai Zhong,2 Zhenxue Jiang ,1 Shijie He,1 Xiaoxue Liu,1 Deyu Zhu,1 Zixin Xue,1 Yuru Zhou,1 and Jiajing Yang2 1State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing 102249, China 2Shale Gas Research Institute, Southwest Oil & Gas Field Company, PetroChina, Chengdu 610000, China Correspondence should be addressed to Xianglu Tang; [email protected] and Zhenxue Jiang; [email protected] Received 9 November 2020; Revised 27 November 2020; Accepted 8 April 2021; Published 21 April 2021 Academic Editor: Reza Rezaee Copyright © 2021 Xianglu Tang et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Adsorbed gas is an important component of shale gas. The methane adsorption capacity of shale determines the composition of shale gas. In this study, the methane adsorption capacity of marine, transitional, and lacustrine shales in the Sichuan Basin was analyzed through its isothermal adsorption, mineral composition, water content, etc. The results show that the methane adsorption capacity of marine (Qiongzhusi Formation and Longmaxi Formation), transitional (Longtan Formation), and lacustrine (Xujiahe Formation and Ziliujing Formation) shales is significantly different. The Longtan Formation has the strongest methane adsorption capacity. This is primarily related to its high organic matter and organic matter type III content. The methane adsorption capacity of the lacustrine shale was the weakest. This is primarily related to the low thermal evolution degree and the high content of water-bearing clay minerals. Smectite has the highest methane adsorption capacity of the clay minerals, due to its crystal structure. The water content has a significant effect on methane adsorption largely because water molecules occupy the adsorption site. Additionally, the temperature and pressure in a specific range significantly affect methane adsorption capacity. 1. Introduction Shale gas is divided into adsorbed gas, free gas, and dis- solved gas. Adsorbed gas and free gas are the primary forms As a clean fossil resource, natural gas has always been an of shale gas [6]. Adsorbed gas is a popular focus of shale gas important energy source for the world’s industrial and research, largely because the control factors of adsorbed gas economic development. As one of the important types of are complex. According to the different adsorption forces, natural gas, shale gas is an abundant resource, and the adsorption can be divided into two types: chemical adsorp- shale revolution has changed the global oil and gas supply tion and physical adsorption. Physical adsorption is VDW [1–3]. North America and China are the primary regions (Van der Waals’ force) adsorption, which is produced by of commercial shale gas development. In 2019, the pro- the interaction force between the adsorbate and adsorbed duction of shale gas in the United States reached 7151 × molecules. It includes the dispersion force, electrostatic force, 108 m3, accounting for 62.0% of the total gas production, and induction force. Physical adsorption is the principal type the highest production in North America. China’s shale of adsorption for shale gas [7]. gas production reached 154 × 108 m3 in 2019. The Sichuan Adsorbed gas and free gas codetermine the scale of shale Basin is an important petroliferous basin where China’s gas accumulation, and the dominant position of the two shale gas exploration and development has made the most changes with the accumulation conditions, shale, gas mole- rapid progress and the earliest commercial development cules, etc. [8]. The adsorption starts quickly, and the [4, 5]. adsorbed gas molecules are then easily desorbed from the 2 Geofluids 0 25 50 75 km AnKang ZhenBa N GuangYuan Y L 4 MaErKang ChengKou XC 28 LangZhong XY 1 WuShan ChengDu LiangPing LiZhou KangDing W 203 FuLing J S1 NeiJiang ChongQing QianJiang J Y1 J Y 1 GanLuo YouYang Y 202 L 201 ZhengAn MeiGu N 216 JiShou XiChang N HuaiRen ShiQian ZhaoTong BiJie QianXi WengAn China MiYi QiaoJia Sichuan basin XuanWei AnShun DuYun Legend Quaternary Carboniferous Tertiary Silurian Cretaceous Cambrian Jurassic Well location Triassic City Permian Figure 1: Stratum characteristics and sampling locations in the Sichuan Basin. Shales are primarily developed in the Cambrian Qiongzhusi Formation, the Ordovician Wufeng Formation, the Silurian Longmaxi Formation, the Permian Longtan Formation, the Triassic Xujiahe Formation, and the Jurassic Ziliujing Formation. A total of 10 wells and 152 samples were selected for analysis. surface of the shale particles and enter the dissolved and free of the gas adsorption capacity declines [17]. Reservoir tem- phases. When the adsorption and desorption speeds are perature has a great influence on methane adsorption capac- equal, the adsorption reaches a dynamic equilibrium. With ity. The higher the temperature, the lower the methane the massive generation of natural gas, the internal pressure adsorption capacity. The shale gas in the Upper Jurassic Gor- of the shale rises, causing gaps and discharge, and free gas dondale Formation in northeastern Canada has a methane enters the sandstone to form conventional gas reservoirs [9]. adsorption capacity of 0.05–2.00 cm3/g at 60 MPa and 30°C Unlike conventional gas reservoirs, shale has a high con- [18]. Additionally, there is a positive relationship between tent of adsorbed gas [10, 11]. Therefore, it is necessary to organic carbon content and methane adsorption capacity conduct a detailed study on the adsorption capacity of shale [19]. While both clay minerals and kerogen adsorb gas, to determine the various factors that affect its adsorption the adsorption capacity of kerogen is stronger than that capacity. The adsorption capacity of shale is primarily related of clay. Although the adsorption capacity of clay is rela- to the organic carbon content, mineral composition, reser- tively weak, it still contains a large amount of gas and can- voir temperature, formation pressure, shale water content, not be ignored [20, 21]. Only when the water content is gas component, shale density, and pore structure [12–16]. large (higher than 4%) is the gas adsorption capacity of When the formation pressure is low, gas adsorption requires shale significantly reduced, and the gas adsorption capacity a higher binding energy. When the pressure increases, the of samples saturated with water was 40% lower than that required binding energy decreases, and the rate of increase of dry samples [18]. Geofluids 3 Geologic time scale (Ma) Shale Stratigraphic Tectonic Basin Period formations column movements development Legend Age Depositional Era and age environment Neogene (N) 20Ma Hymalayan2 to quaternary orogeny Rejuvenated foreland basin Paleogene (E) 40Ma Hymalayan1 Cenozoic orogeny Clay -100 Cretaceous 100Ma Yanshanian (K) orogeny Intracontinental Limestone Lacustrine subsidence Jurassic (J) Marlstone Mesozoic Ziliujing Peripheral -200 210Ma Indosinian foreland basin Xujiahe Triassic (T) orogeny Passive margin Glutenite Longtan Permian (P) Emei basalt Hercynian- Shale -300 Indosinian Carboniferous Transitional (HI) (C) Marginal (coastal swamp) Dolomite extension Devonian (D) Qilian -400 400Ma orogeny Sandstone (Pz) Late Ca Paleosozoic Silurian (S) Foreland basin Longmaxi Caledonian Syenite Ordovician orogeny (Ca) (O) Marine -500 Passive margin Cambrian 510Ma Salairian (E) Qiongzhusi orogeny (SI) Pre- Sinian (Z) Early continental -600 Cambrian rift Figure 2: Structural evolution and Stratigraphic histogram of Sichuan Basin. The Qiongzhusi Formation, Wufeng Formation, Longmaxi Formation, Longtan Formation, Xujiahe Formation, and Ziliujing Formation shales are primarily developed in the Sichuan Basin. There are multiple sets of shale formations in the Sichuan are marine shale, the Permian is transitional shale, and the Basin, China. The occurrence status of marine shale, transi- Upper Triassic and Lower Jurassic are lacustrine shales. tional shale, and lacustrine shale gas is not clear, and the These shales have reached the standard of effective gas influence of shale reservoir parameters and the external envi- sources, especially the marine shale, which has many layers ronment on shale gas adsorption capacity has not been deter- and a wide distribution, and have entered a high and overma- mined. The microscopic mechanisms of shale gas adsorption ture stage, with a higher gas generation rate [22–24]. have not been clarified, which hinders the understanding of The evolution of the Sichuan Basin goes through five shale gas formation. Thus, we selected typical marine shale stages, namely, the Presinian basement formation stage, the (Qiongzhusi Formation with 27 samples, Longmaxi Forma- Sinian-Middle Triassic kratogen basin stage, the Late Triassic tion with 54 samples), transitional shale (Longtan Formation foreland basin stage, the Early Jurassic–Late Cretaceous with 37 samples), and lacustrine shale (Xujiahe Formation depression basin stage, and the Cenozoic tectonic basin stage with 19 samples, Ziliujing Formation with 15 samples) in (Figure 2). The Sinian-Middle Triassic is dominated by the Sichuan