## 4 Discussion
The more complex and diverse the microbial community structure, the more stable the ecosystem will be. When the external environment changes, a stable ecosystem can play a buffering role [35]. Based on the results obtained in the previous text, we can know that the WF block contained more microorganisms with functions such as fermentation, hydrocarbon degradation, aromatic degradation, nitrate respiration, nitrogen respiration, and nitrate reduction than the ASP block. Fermentation refers to the process of directly transferring the electrons released from the oxidation of organic matter under anaerobic conditions to some intermediate product of the substrate itself that is not fully oxidized, while releasing energy and producing various metabolic processes. During the fermentation process, large-molecule fatty acids, amino acids, and other substances produced during the aerobic stage can be further degraded to produce small-molecule short-chain fatty acids, H\({}_{2}\), CO\({}_{2}\), and other substances. Hydrocarbon metabolism is the main metabolic activity of reservoir microorganisms in the formation. [PERSON], [PERSON] et al. found, in their research under high temperature and pressure conditions, that indigenous microorganisms in reservoirs have certain activity, which can significantly reduce the residual oil amount of remaining oil [36]. By analysing past community structures, the diversity of microbial composition, and the influence of environmental factors on microbial communities, it is clear that microbial communities typically exhibit remarkable taxonomic diversity [19]. This raises questions about the mechanisms of species coexistence and the importance of this diversity for community function. Large numbers of coexisting but classified microorganisms may encode the same energy-producing metabolic function, and the population encoding each function may undergo significant changes in space or time with a minimal impact on function. Suchdifferences in classification are often attributed to ecological drift between equivalent organisms [37; 38; 39]. An assessment of the microbial diversity involved in different metabolic functions also suggests that communities generally exhibit a high degree of 'functional redundancy' across multiple functional aspects. This means that each metabolic function can be performed by several coexisting organisms with different taxonomic classifications [40; 41]. In summary, we found that the WF block had the necessary oil recovery function and high redundancy for the implementation of microbial oil recovery, which is a good basis for the implementation of microbial flooding. Chemical composition also influences the distribution and composition of microbial communities inhabiting subsurface oil reservoirs. Differences between microbial communities from different oil wells could even be explained by the different environmental conditions [42]. A canonical correspondence analysis (CCA) reported that the taxonomic composition of Qinghai oil wells had a positive correlation with aliphatic and aromatic hydrocarbons and a negative correlation with polar fractions containing nitrogen, sulphur, and oxygen heteroatoms from crude oil [43]. Bacterial groups of _Bacteroidetes, Alpha-Proteobacteria_, and _Actinobacteria_ showed positive correlation with NO3- concentration, _Gamma-Proteobacteria_, and _Chloroflexi_ with SO4- and PO4- concentration. A positive correlation with acetate concentration was found for members of _Firmicutes_ and the genus _Methanothermobacter_[44]. The bacterial composition in the produced water of Algerian oil fields was significantly correlated with salinity, Cl-, and K+ [45]. A high-throughput sequencing analysis revealed new biochemical capabilities in reservoir systems. As a basis for the implementation of future microbial enhanced oil recovery, we aim to investigate the relationship between reservoir microorganisms and environmental factors to improve our understanding of how to stimulate the rapid growth and proliferation of endogenous microorganisms.