Period Covered by Report: September 1, 2002 through November 30, 2002
Date of Report: January 14, 2003
EPA Agreement Number: R 827015-01-0
Title: Evaluation of Commercial, Microbial-Based Products to Treat Paraffin Deposition in Tank Bottoms and Oil Production Equipment
Investigators: L. M. Gieg, M. J. McInerney, and J. M. Suflita
Institution: University of Oklahoma
EPA Project Officer: Bala Krishnan
Project Period: June 1, 2002 through May 31, 2003
Project Amount: $149,999
Research Category: Wellbore Cleanout
Petroleum, bioremediation, microbiology
We aim to determine the mechanism(s) of action of commercially available, microbial formulations used to treat paraffin deposition in the oil field. Because there are many conflicting reports by producers on the efficacy of microbial treatments to remedy paraffin deposits, it is not known why microbial treatments work under some conditions but not others. Knowledge of the mechanism(s) used by microorganisms to remediate paraffin deposits is a critical first step to understanding how the application of microbial treatments for paraffin removal can be optimized in the oil field. The results of this study will benefit the domestic oil industry because understanding the mechanisms of action of these products will allow the independent producer to determine the conditions under which these products are likely to succeed and to determine if and when the purchase of microbial commercial paraffinic treatments represents a wise expenditure of investment dollars.
We are conducting the preliminary screening process using a crude oil selected by Phillips Petroleum (now Conoco-Phillips) for this research project. This oil is designated Alaska Oil A. A second oil for study has been selected, but preliminary screening has not yet been conducted.
To conduct the preliminary screening process for the first oil, Alaska Oil A was incubated in the presence (test bottles) and absence (control bottles) of Microbial Product A under aerobic and anaerobic conditions incubated at both room temperature and at 60°C. Microbial Product A was selected by a microbial formulation proprietor to be suitable for the treatment of paraffins present in Oil A. Each test incubation vessel contained 85 mL of an artificial seawater medium, 10 mL of oil, and 5 mL of Microbial Product A. In the microbial-free controls, the incubation vessels contained 90 mL of medium and 10 mL of oil. The seawater medium used for aerobic and anaerobic incubations was identical except that the anaerobic medium contained a higher amount of bicarbonate for buffering with a 20% CO2 in N2, resazurin as a redox indicator, and a reductant (cysteine-sulfide). As per recommended protocol by the microbial formulation proprietor, the bottles were incubated for 3 days under the appropriate conditions with slow end-over-end mixing. Duplicate bottles were also incubated anaerobically at the two temperatures for a longer period of time, in case additional time was needed for microbial activity in the absence of oxygen. After these incubation periods, a portion of the oily layer from each bottle was removed and analyzed for any changes in the wax appearance temperature (WAT). The WAT test measures the temperature at which paraffin crystals begin to form when an oil is cooled under controlled conditions. For the purposes of this research, microbial paraffin treatments which lower the WAT by a minimum of 5% over that of the parallel microbial-free controls are considered successful.
Of the WAT tests conducted to date, no bottles incubated under anaerobic conditions showed a reduction in WAT. In contrast, one of the three replicates incubated aerobically at 60°C showed an 8% reduction in the WAT relative to a microbial-free control. Similarly, an aerobic incubation at 25°C showed a reduction in the WAT of 5.6% relative to a control. For the aerobic bottles, a thick emulsion layer was observed at the oil-water interface after the 3-day incubation whereas little emulsion was seen for the anaerobically-incubated bottles. Emulsification of the oil may be indicative of changes in the paraffin composition due to microbial treatment. However, this has yet to be tested in the more detailed mechanism experiments.
Analytical methods to monitor for any changes in the paraffin composition due to microbial treatment of the oils are currently being established. Gas chromatography (GC) with flame ionization detection will be used for the paraffin analysis. An on-column injector has been installed into an HP 6890 GC and samples will be analyzed using simulated distillation GC with a MXT-1HT column (Restek). The GC method will analyze samples in the track oven mode in order to obtain good resolution and detection of high molecular weight paraffins. Standards up to C100 (Supelco) will be used for calibration and to monitor method performance. Once the method is established, the preliminary screening samples showing a reduction in the WAT after treatment will be analyzed for any changes in the paraffin composition relative to controls and/or treatments which did not show a WAT reduction. Similarly, the aqueous layers from the preliminary screening tests will be extracted with organic solvent and analyzed by GC-mass spectrometry to determine whether paraffins have undergone biodegradation. Further detailed studies examining the mechanism of the microbial paraffin treatment process will be carried out once the initial screening tests and analysis for Alaska Oil A is completed.