Effects of Montmorillonite on Crude Oil Biodegradation and the Microbial Community in an Oil Production Well Pad Shut Down for 753 Days

Clay-mediated microbial degradation has been demonstrated as a low-cost, efficient, and eco-friendly strategy for remediating crude oil-contaminated soils. Despite substantial laboratory studies, field tests remain scarce. In this study, montmorillonite treatment was applied to a crude oil production well pad shut down for 753 days. Post-treatment analyses included soil physicochemical parameters (water content, redox potential, pH, elemental analysis, and total organic carbon), crude oil content/composition (gas chromatography–mass spectrometry), microbial biomass (deoxyribonucleic acid concentration), and community structure (high-throughput sequencing), with parallel comparisons to untreated control areas. Results indicated that montmorillonite enhanced the crude oil biodegradation rate (37.27% vs. control 33.00%), increased microbial biomass (83.08% vs. control 35.06%), and enriched biodiversity (7 genera vs. control 0). Specifically, it exhibited the most pronounced promotion effects on saturated hydrocarbon degradation (73.42% vs. control 60.89%) and aromatic hydrocarbon degradation (45.77% vs. control 29.60%). This study not only provides field evidence for clay-mediated microbial remediation but also lays a foundation for developing composite remediation approaches (e.g., nutrient supplements, catalysts, or functional microbial consortia) in future research and practical applications.