Methanogenesis Potentials: Insights from Mineralogical Diagenesis, SEM and FTIR Features of the Permian Mikambeni Shale of the Tuli Basin, Limpopo Province of South Africa

Abstract

Carbonaceous shale is more topical than ever before due to the associated unconventional resources of methane. The use of FTIR, SEM-EDX, and mineralogical analyses has demonstrated a promising approach to assess methanogenesis potentials in a more rapid and reliable manner for preliminary prospecting. Representative core samples from the borehole that penetrated the carbonaceous Mikambeni shale Formations were investigated for methanogenesis potentials. The absorption band stretches from 1650 cm−1 to 1220 cm−1 in wavenumber, corresponding to C-O stretching and OH deformation of acetic and phenolic groups in all studied samples, thereby suggesting biogenic methanogenesis. The CO2 was produced by decarboxylation of organic matter around 2000 cm−1 and 2300 cm−1 and served as a source of the carboxylic acid that dissolved the feldspar. This dissolution process tended to release K+ ions, which facilitated the illitization of the smectite minerals. The SEM-EDX spectroscopy depicted a polyframboidal pyrite structure, which indicated a sulfate reduction of pyrite minerals resulting from microbial activities in an anoxic milieu and causes an increase in alkalinity medium that favors precipitation of dolomite in the presence of Ca and Mg as burial depth increases. The contact diagenesis from the proximity of Sagole geothermal spring via Tshipise fault is suggested to have enhanced the transformation of smectite to chlorite via a mixed layer corrensite in a solid-state gradual replacement reaction pathway. The presence of diagenetic chlorite mineral is characteristic of low-grade metamorphism or high diagenetic zone at a temperature around 200 °C to 230 °C and corresponds to thermal breakdown of kerogen to methane at strong absorption band around 2850 cm−1 and 3000 cm−1, indicating thermal methanogenesis.

Clay mineral nanostructures regulate sequestration of organic carbon in typical fluvial sediments

“…The spectra were collected over 64 scans in the range of 4000–400 cm −1 with a resolution of 4 cm −1 . Band positions were assigned based on previous investigations and by considering the predominant clay mineralogy of the samples [ [31] , [32] , [33] , [34] ].…”

Review of the Effect of Diagenetic Evolution of Shale Reservoir on the Pore Structure and Adsorption Capacity of Clay Minerals

“…Smectite initially contains more than four layers of water molecules. At this stage, except for structural water, the rest is discharged, and the structure and physical properties of shale changed due to the accompanying compaction and cementation. − The contact between particles changes from linear contact to concave-convex contact. , With diagenetic evolution and chemical compaction, mixed I/S content gradually decreases and Illite content increases, and the orientation of clay minerals further improves. − The transformation of clay minerals also leads to the change of adsorption capacity. Circular and slit micropores with large specific surface area are developed in smectite, resulting in the largest CH 4 adsorption capacity in all clay minerals.…”

Adsorption Characteristics of Ionic Surfactants on Anthracite Surface: A Combined Experimental and Modeling Study

“…It was purchased from Thermo Fisher Scientific Corporation in Shanghai, China. Before the experiment, the raw coal samples, the samples after SDBS and STAC adsorption with anthracite, and KBr solid powder reagents were dried in a vacuum-drying oven to remove moisture, and the influence of moisture on the infrared test was excluded [40,41]. A 2 mg powder sample and 200 mg pure KBr were ground according to the ratio of 1:100.…”