Evaluation of a Glutaraldehyde/THNM Combination for Microbial Control in Four Conventional Oilfields

Abstract

The performance of a new synergistic biocide combination based on glutaraldehyde and THNM (tris (hydroxymethyl) nitromethane) was extensively evaluated in laboratory trials using water samples from twenty-six Brazilian and Argentinian oilfields. The performance was ultimately validated in four field trials, two per country (A1, A2, B1, B2), over a three month duration. For laboratory tests, water samples were collected from numerous locations of the various oilfields and characterized/enumerated by serial dilution (SRB and APB bug bottles), ATP, and molecular biology techniques (NGS). Water and isolated indigenous SRB/APB from the most contaminated locations were used as the matrix and test inoculum for the biocide optimization tests. Numerous biocide systems, at total active ingredient concentrations ranging from 111 to 250 ppm, were evaluated by assessing the ability to rapidly kill the native organisms (2 hour contact time at room temperature) and protect the water from contamination over a prolonged time frame (≥7 days) under heat-aged conditions (60°C). Results demonstrated that glutaraldehyde/THNM provided the best performance in the majority of the samples evaluated and was therefore selected for performance evaluations in field tests owing to the enhanced performance of this particular treatment in the laboratory. Field trials were conducted by applying the lowest total biocide concentration that demonstrated a ≥ 4 log10 microbial reduction (in the laboratory studies) at various problematic field locations. All biocides were dosed as batch treatments 2-3 times per week (2-3 hours per treatment). Specifically, the co-dosed glutaraldehyde/THNM combination replaced incumbent treatments of either THPS or glutaraldehyde (batch dosed) in combination with a quaternary ammonium compound which was being applied by continuous injection: Field trial B1 – Results showed a significant reduction in bacterial counts at the farthest injection well (12 km from the point of biocide application). Total anaerobic bacteria levels were reduced from ~106 CFU/mL to less than 102 CFU/mL after 1 month treatment. Additionally, total biocide consumption was reduced by 24% as compared to the incumbent biocides traditionally applied. Field trial B2 – Following treatment of injection water, SRB results showed a reduction at the farthest injection well (30 km), from 103 cells/mL to 101 cells/mL, after 3 months treatment. Field trial A1 – After applying glutaraldehyde/THNM to production and injection water, SRB/APB levels were reduced (~108 CFU/mL to 102 CFU/mL) at the farthest injection well (7 km) after 1 month treatment. Field trial A2 – Following the treatment of production and injection water, all monitored points demonstrated a reduction of SRB counts from ~107 CFU/mL to 102-103 CFU/mL after 6 weeks. Furthermore, in the B1 and A1 trials, NGS results indicated a shift of the microbial population to less harmful (non-MIC relevant) organisms. Overall, the novelty of this biocide combination is its ability to provide strong, broad-spectrum antimicrobial performance and long-term effectiveness, as compared to traditional biocide chemistries.