1 Introduction
Understanding the mechanisms of biospheric characteristics in coal
reservoir is important to CBM exploration (Tang et al., 2012; Wei et
al., 2014; Guo et al., 2015; Wang et al., 2019). C-N-S microorganisms
such as methanogens, nitrifying bacteria, denitrifying bacteria and
sulfate reducing bacteria, play an important role in controlling the
accumulation of coalbed methane, especially biogenic gas (Guo et al.,
2012; Pashin et al., 2014; Schweitzer et al., 2019). Although such
microorganisms regulate most biosphere processes related to fluxes of
greenhouse gases like CO2, CH4 and
N2O, little is known about their role in coal reservoir.
Through the systematically collection of water samples from coalbed
methane wells in Southern Qinshui Basin for microbial sequencing and
geochemical testing, it will show whether microorganisms’ distribution
changed in different hydrogeochemical zones of the coal seam.
Microorganisms mediate biogeochemical cycles of carbon (C), nitrogen
(N), phosphorus (P), sulphur (S) in ecosystem dynamics. Fast developing
metagenomic technologies allow us to explore the distribution
characteristics and mechanism of microorganisms (Zhang et al., 2015;
Wong et al., 2018). Integrated metagenomics technologies such as 16s RNA
sequencing was used to determine the microbial community structure and
functions structure in high rank coal ecosystem in Qinshui Basin.
Environmental factors such as redox conditions, pH, temperature and ion
concentrations play an important role in controlling the distribution of
various types of microorganisms, especially C-N-S microorganisms
(Schlegel et al., 2011; Barnhart et al., 2013). These environmental
factors are significantly changed in different hydraulic zones of
Southern Qinshui Basin (Zhang et al., 2015). Therefore, this study
predicts that hydrological conditions have important controlling effect
on C-N-S microorganisms. The aim of this study is to find whether there
is shifting microbial function composition from different hydrological
zones, such as from runoff area to stagnant area. This study also tries
to explain that if different microbial populations in different
hydrological zones would have differential geochemical responses and
that if weakened hydrodynamic conditions would greatly stimulate the
functional genes involved in nutrient-cycling processes.
Southern Qinshui Basin located in north China craton is one of the most
highly developed CBM region (Fig.1a) (Wang et al., 2016). Shizhuangnan
block, in adjacent to Fanzhuang block and Zhengzhuang block (Fig.1b), is
located in the transition area from the southeast edge of the basin to
the deep part (Fig.2b). 3# coal seam is the main gas producing layer.
The elevation of 3# coal is 223~597m (Fig.2b), and the
coal thickness is 4.45~8.75m (Fig.2d). 3# coal seam in
the study area has the highest coal rank
(Romax 2.92~3.02%)
(Fig.2c) and the highest gas content (8~25
m3/t) in Qinshui Basin (Fig.2a). Now there are more
than 1000 drainage wells in this block (Fig.1c). The daily average gas
production of 570 drainage wells in Shizhuangnan block was counted and
the gas production of most wells exceeded 1000 m3/d.
Moreover, high production wells were mainly distributed in the west of
the block (Zhang et al., 2016).
Hydrogeological condition is an important controlling factor of coalbed
methane enrichment (Xu et al., 2015; Yao et al., 2014). As the coal
bearing strata in the study area are monoclinic structures extending
from east to west, the synclines in the west weaken the hydrodynamic
strength, the temperature and redox environment of the study area change
dramatically from the oxidation runoff belt in the east of the basin
edge to the deep stagnant area in the west (Zhang et al., 2015), making
it an ideal area to research microbial distribution difference, the
hydrogeological conditions of the study area will be introduced below.