One of the challenges indigenous microbial enhanced oil recovery (MEOR) is facing is the high percentage of divalent ions, which obstruct the growth and metabolism of microorganisms and destabilize the oil-in-water (o/w) emulsion. Six formulas were selected for the stimulation of indigenous microbes and to compare their performances on the oil emulsification and oil spreading in the Luliang oilfield containing Ca2+-rich brine. Illumina MiSeq sequencing of 16S rRNA genes was applied to investigate the structural response of microbial communities to various formulas. The results showed that the addition of proper organic phosphorus and the optimal P/N ratio (0.01) can facilitate production of biosurfactant and create stable o/w emulsion with specific reservoir condition containing Ca2+-rich brine, through direct stimulation of certain functional microbes. This study provides a promising path for direct enrichment of biosurfactant-producing and oil-degrading Dietzia genus and a potential instructional approach of indigenous MEOR in Luliang oilfield.

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