Lab-Scale Experimental Study of Microbial Enhanced Oil Recovery on Low-Permeability Cores Using the Silicate Bacterium Paenibacillus mucilaginosus

Silicate bacteria, capable of decomposing silicate minerals that are widely distributed in oil reservoirs, have never been applied in microbial enhanced oil recovery (MEOR). This study investigated a typical silicate bacterium (<i>Paenibacillus mucilaginosus</i>) for the first time in a simulation experiment on low-permeability cores. Meanwhile, a biosurfactant-producing bacterium (<i>Pseudomonas aeruginosa</i>) and an acid-producing bacterium (<i>Bacillus licheniformis</i>) that have been widely studied and applied in MEOR were used for comparison. The results show that although <i>P. mucilaginosus</i> is inferior to <i>P. aeruginosa</i> and <i>B. licheniformis</i> in terms of enhancement of oil recovery at the microbial flooding stage, it can maintain efficient dissolution of minerals over extended periods during the subsequent water flooding stage. This is different from the other two bacteria and ultimately leads to a 6.9% enhancement in oil recovery (7.9% for <i>P. aeruginosa</i> and 4.8% for <i>B. licheniformis</i>). <i>P. mucilaginosus</i> improves oil recovery by increasing the porosity (1.4%) and permeability (12.3 mD) of low-permeability cores through biological weathering. The μCT results show that the pore quantity and pore volume across varying pore radii in low-permeability cores are altered after the MEOR simulation experiment by reducing the quantity and volume of pores with radii less than 10 μm and increasing the quantity and volume of pores with radii between 10 and 25 μm. Under MEOR simulation experimental conditions, <i>P. mucilaginosus</i> slightly degrade saturated hydrocarbons (1.9%), mainly the n-alkanes of C11-C20, but cannot degrade aromatic hydrocarbons, resins, and asphaltenes. The enhanced oil recovery by <i>P. mucilaginosus</i> is attributed to its bio-dissolution under neutral pH conditions, which prevents acid sensitivity damage to low-permeability cores. Thus, its MEOR characteristics are significantly different from the biosurfactant-producing bacterium <i>P. aeruginosa</i> and acid-producing bacterium <i>B. licheniformis</i>. Injecting <i>P. mucilaginosus</i> at the early stages of reservoir development or using it together with other microorganisms should maximize its MEOR effect. This study advances the MEOR framework by extending silicate-dissolving bacteria from agricultural microbial fertilizer systems to MEOR in low-permeability reservoirs, revealing the broad prospects of mineral-targeting microbes for both research and industrial applications in MEOR.