Biogeochemistry and Water–Rock Interactions of Coalbed Methane Co-Produced Water in the Shizhuangnan Block of the Southern Qinshui Basin, China

Abstract

Coalbed methane is a major unconventional resource that has been exploited commercially for decades in the southern Qinshui Basin of China. The hydrogeochemical characteristics of coal reservoir water play a key role in the exploration and development of coalbed methane resources. In view of this, a detailed study was performed on coalbed methane co-produced water collected from the Shizhuangnan block to assess water–rock interactions and biogeochemical processes. Water samples were analyzed to establish major ions, isotopic compositions and perform 16S rRNA sequencing. Results suggest that the hydrochemistry was controlled by water–rock processes and that methane was consumed by sulfate reduction through calculation. Meanwhile, the isotopic compositions of water samples indicated that they had a predominantly meteoric origin and were influenced by microbial activity. The 16S rRNA sequencing results of bacteria and archaea provide an important foundation for understanding the activity of sulfate-reducing bacteria and methanogens at different hydraulic heads, which was consistent with isotopic analysis. Carbonates containing calcite and dolomite were found to be distributed at different hydraulic head due to the biogeochemical characteristics and associated water–rock interactions.

Biogeochemical Assessment of the Coalbed Methane Source, Migration, and Fate: A Case Study of the Shizhuangnan Block, Southern Qinshui Basin

“…3 coal seam used in the study area is 6 m, and the total buried depth is about 450−900 m. The overall coal seam shape shows a trend of shallowness in the southeast and depth in the northwest. 8,14 In this study, the No. 3 coal seam is the primary source of samples.…”

Hydrogeochemical Characteristics and Water–Rock Interactions of Coalbed-Produced Water Derived from the Dafosi Biogenic Gas Field in the Southern Margin of Ordos Basin, China

“…According to Figure 7(c), the ratio of [(Ca 2+ +Mg 2+ )-(SO 4 2-+HCO 3 -)] and (Na + +K + -Cl -) ≈ -1, illustrating the cation exchange between Na + and Ca 2+ /Mg 2+ , is relatively common. Chloroalkaline index (CAI) can also be regarded as the quantified cation exchange degree [44]. In the study area, CAI-I and CAI-II were almost all negative (Figure 7(d)), and their values differed substantially, indicating that differing levels of water-rock interactions occurred during groundwater migration [45].…”

“…Generally, the relationship between [(Ca 2+ +Mg 2+ )-(SO 4 2-+HCO 3 -)] and (Na + +K + -Cl -) can be used to determine whether or not cation exchange has occurred [44]. According to Figure 7(c), the ratio of [(Ca 2+ +Mg 2+ )-(SO 4 2-+HCO 3 -)] and (Na + +K + -Cl -) ≈ -1, illustrating the cation exchange between Na + and Ca 2+ /Mg 2+ , is relatively common.…”

The effects of supercritical CO2 on the seepage characteristics and microstructure of water-bearing bituminous coal at in-situ stress conditions

“…Several studies have highlighted the important role of water in geochemical interactions (Li et al, 2019). Renxia Jiang et al conducted a ScCO 2 -H 2 O interaction experiment on coal to investigate the effect of ScCO 2 -H 2 O on the primary mineral composition of coal.…”