Period Covered by Report: December 1, 2002 through February 28, 2003
Date of Report: April, 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: 6-1-02 to 5-31-03
Project Amount: $149,999
Research Category: Wellbore Cleanout
Keywords: Petroleum, bioremediation, microbiology
Objective: 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 they are likely to succeed and to determine if and when the purchase of microbial commercial paraffinic treatments represents a wise expenditure of investment dollars.
Progress Report/Accomplishments: We have completed the preliminary screening process of a crude oil (Alaska Oil A) selected by Conoco-Phillips Petroleum for this research project. This entailed incubating the oil with an artificial brine medium in the absence (controls) or presence (tests) of a proprietary microbial product chosen specifically to treat this oil. Tests were conducted at room temperature (~24 °C) and at 60 °C either in the presence or absence of oxygen. All incubations were in triplicate. After 3 days of incubation with slow end-over-end mixing, oil layers were removed to conduct the wax appearance temperature (WAT) test. This test measures the temperature at which paraffin crystals begin to form when an oil is cooled under controlled conditions using cross-polarized microscopy. 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 on Alaska Oil A, no bottles incubated under anaerobic conditions showed a reduction in the 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 but this remains to be tested. Despite these observations, ANOVA analysis showed that there was no significant difference in the WAT between the test and control samples, suggesting that the proprietary microbial product selected to treat this oil was ineffective, at least over the 3-day incubation period. However, this data set was confounded by the observation that many of the control WAT values obtained were somewhat erratic. It was assumed that the oil removed from the controls would have similar WATs but the values were found to differ by as much as 5 °C among treatments. In contrast, conducting the WATs on the oil alone (e.g., oil not mixed with an aqueous phase as in the incubations) showed consistent WAT values. We have also carried out viscosity measurements on both the oil alone, and oil removed from the preliminary incubations. We found that viscosity measurements of the pure oil were reproducible, but those for oil layers removed from the aqueous incubations were not. These observations suggest that water itself has an effect on this oil, making it difficult to discern the effects of microbial product addition. Several attempts to optimize viscosity measurements on the oil samples have not yielded reproducible results, thus we will no longer be using viscosity to measure changes in paraffing reduction. However, we are currently optimizing the use of the cross-polarized microscopy technique for measuring WATs and preliminary results have yielded more reproducible results. We will also be exploring the use of differential scanning calorimetry to determine WATs (this instrumentation for this measurement was recently acquired as a result of the Conoco- Phillips merger).
The aqueous phases of controls and the two treatment bottles showing a reduction in the WAT with respect to appropriate controls were extracted under acidic conditions with ethylacetate, silylated, and subjected to GC- MS analysis to look for microbial metabolites of oil components. Using this method, no presumed alkane metabolites, such as alkanoic acids or alkanols, were detected in the aqueous phases of the treatment bottles relative to the controls.
A second oil selected by ConocoPhillips, designated Alaska Oil B, has also undergone the preliminary screening tests as described above but with some modifications. We have speculated that the lack of success of treatment with Alaska Oil A may have been due to an abbreviated incubation time, oxygen-limitation in the aerobic incubations, and that the controls themselves may be influenced by differing treatments. Thus, for the screening of the second oil, we incubated the test and control bottles for a longer time period (7 days), and added oxygen to the aerobic incubations on a daily basis. We are in the process of conducting the WATs on the control incubations initially in order to determine how variable these values may be among treatments.
Analytical methods to monitor for any changes in the paraffin composition due to microbial treatment of the oils are under development. High- temperature gas chromatography (HTGC) with flame ionization detection is being used to analyze the paraffin composition of treated and untreated oil samples. An on-column injector has been installed into an HP 6890 GC and samples are analyzed using simulated distillation GC with a MXT-1HT column (Restek). The GC method analyzes samples in the track oven mode (to simulate distillation) in order to obtain good resolution and detection of high molecular weight paraffins. Standards up to C100 are being used for calibration and to monitor method performance. We are still optimizing oil sample analysis with this system, but analysis of standards have been reproducible and as expected from supplier information. Once this analytical method is firmly established, the preliminary screening samples from Alaska Oils A and B 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. Further detailed studies examining the mechanism of the microbial paraffin treatment process will be carried out once the initial screening tests and analyses for Alaska Oil B are completed.