Fig. 1

Temporal variations in the microbiota of production water (PW) (n = 143), sandstone cores (n = 24), and production oil (n = 3). a Location of the study site and oilwell information of the field experiment, illustrating the operation mode of one-well injection and four-well production. b The field trial design, sampling scheme, and oil production details. Initial oil recovery was accomplished by conventional cold approaches, while our microbial modulation strategy was applied by injecting exogenous bacteria in four batches, accompanied by a shut-in period. Cumulative crude oil production was intensively monitored and documented throughout the investigation period. c Bacterial α–diversity of production water and sandstone cores was examined by the Shannon index showing the richness and evenness of microbiota. Different letters above violin plots indicate significant differences (Kruskal–Wallis nonparametric rank-sum test, P < 0.05). d Bacterial β–diversity of principle coordinates analysis (PCoA) based on Bray–Curtis distance. e Bacterial composition at the phylum level. f Bacterial composition at the genus level