Neem-Based Green Biocide for Mitigating Crude Oil Souring: Inhibition of Sulfate-Reducing Bacteria

Abstract

Crude oil souring, driven by the metabolic activity of sulfate-reducing bacteria (SRB), presents significant operational and environmental challenges in petroleum production. The generation of hydrogen sulfide (H₂S) by SRB contributes to reservoir plugging, infrastructure corrosion, decreased oil quality, and increased processing costs. Conventional synthetic biocides used to control SRB activity often exhibit environmental persistence and toxicity, raising concerns over long-term ecological safety. This study investigates the potential of neem (Azadirachta indica) extracts as a green, sustainable biocidal alternative for SRB mitigation. Neem leaves were harvested, dried, and subjected to aqueous and ethanolic extraction. The phytochemical constituents of the extracts were analyzed using the method of Gas Chromatography (GC) and Fourier Transform Infrared Spectroscopy (FTIR), revealing the presence of bioactive compounds including azadirachtin, nimbin, and quercetin. Anaerobic inhibition assays were performed using Desulfovibrio spp. under simulated oilfield conditions. Over a 14-day incubation period, key parameters such as sulfate concentration, hydrogen sulfide production, pH, redox potential, and microbial biomass were systematically monitored. The results demonstrated significant suppression of SRB activity in neem-treated setups, with ethanolic extracts showing higher efficacy. H₂S levels were reduced by over 70% compared to untreated controls, while sulfate reduction rates and microbial growth were notably diminished. FTIR spectra indicated potential cell wall disruption, and GC data supported the antimicrobial role of specific neem phytochemicals. These findings confirm the promise of neem-based biocides as effective, lowtoxicity, and biodegradable alternatives for managing microbial souring in petroleum systems, contributing to more environmentally responsible oilfield operations.