Profile control and plugging ability of extracellular polymeric substances (EPS) produced by E. cloacae strain ZL-02 under Ba²⁺ in reservoir

Microbial Enhanced Oil Recovery (MEOR) is a pivotal technology for enhancing tertiary oil recovery. The production of partly extracellular polymeric substances (EPS) by Enterobacter cloacae exhibits excellent control over mobility and holds promise for applications in heterogeneous reservoir exploration. To investigate the impact of Ba²⁺ on microbial EPS production, a series of tests were conducted, including EPS production tests, polysaccharide and protein content analyses, Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES) measurements, X-ray diffraction (XRD), laser particle size measurements, and transcriptome analysis.The results demonstrated the stimulating effect of Ba²⁺ on EPS membrane production. Ba²⁺ stimulation led to increased secretion of proteins (5.82 g/L) and polysaccharides (9.0 g/L). Moreover, the binding of proteins with Ba²⁺ resulted in an enlargement of the particle size of the EPS membrane and an increase in grain size, reaching a maximum crystallinity of 77.77 %. Transcriptome analysis revealed the up-regulation of 790 genes and down-regulation of 728 genes in response to Ba²⁺ addition. Enrichment analysis of the up-regulated genes highlighted the significant enrichment of gene ontology number GO: 00160120, which directly influenced microbial EPS membrane production. Furthermore, microscopic displacement and core flooding experiments were conducted to evaluate the plugging ability of microbial-produced EPS membranes. Remarkably, under the influence of Ba²⁺, microorganisms exhibited significantly enhanced sealing capacity on glass slides etched with rock cores. The results from simulated flow experiments demonstrated a maximum sealing rate of 81.5 % on rock cores, with an RF (Resistance Factor) value of 2.5 and an RRF (Residual Resistance Factor) value of 5.45. This study innovatively explores oil-producing microbial genes, combining simulation experiments and rock core slicing to reveal the microscale mechanism of Ba²⁺ stimulating microbial EPS secretion for reservoir plugging. It provides theoretical support for the application of MEOR technology in improving oil recovery rates.