Abstract

Paraffin deposition downhole is a major factor influencing well profitability. We have developed a microbial consortium and treatment procedure that produces significant levels of bio-surfactants, bio-emulsifiers and pseudo-solubilization factors that effectively inhibit paraffin deposition. These active agents are continuously produced by the microbial community downhole and serve to water-wet the pipe surfaces and inhibit paraffin accumulation. These factors serve as crystal modifiers and slow down the agglomeration of asphaltenes and paraffins. Some of these surfactants appear to be produced as the shorter chain length alkanes are oxidized to fatty acids. Other bio-surfactants are produced that permit microbial cells to attach to paraffin particles and thus disperse the wax. Extra-cellular bio-surfactants are also produced that aid in this process. These cultures actively metabolize the long chained paraffins making them more water soluble and less likely to attach to pipe surfaces.

Since 1987 we have treated over one thousand separate oil wells with bacteria to control wax and have gathered considerable empirical data that indicates a mixed microbial population periodically added to producing oil wells can help prevent the deposition of wax solids on production equipment. In an attempt to understand what mechanisms provide this beneficial action we have examined the metabolism of various crude oils under strict anaerobic, micro-aerophilic and aerobic conditions. In all cases the medium was supplemented nitrate.

We have noted that because of the wide variety of compounds present in crudes there is a corresponding variety in the rate of metabolism of the components in the crudes. Microbes are capable of dispersing a large number of hydrocarbons (1,2,3,5,7) and we have observed that they will emulsify a much wider range of hydrocarbons than they can metabolize.

When the bacterial cultures were are using are grown under anaerobic conditions on a medium containing yeast extract, malic acid, citric acid and crude oil, they emulsify the oil but cause no detectable decrease in the concentration of the saturated alkanes.

Many of the bacteria are directly associated with oil droplets. These bacteria completely cover all of the surface of the oil. The rest of the bacteria are free from the oil and appear to be growing on the solubilized hydrocarbons.

An interesting observation occurred when bacteria were allowed to grow on 5.0 ml of crude oil for 24 hr prior to the addition of wax. A production wax crude oil mixture warmed to about 50ºC was then added to the medium and agitated for 2 minutes at 35ºC. On the control flask treated with 2% formaldehyde prior to incubation the wax congealed and formed chucks on the surface of the medium. In the live culture flask the wax dispersed into a film on the surface of the medium.

The bacteria we are using in our cultures are capable in the absence of oxygen to use nitrate as the terminal electron acceptor. This process is called anaerobic respiration and provides more energy than fermentation. However, the oxidation of the saturated alkanes requires the presence of molecular oxygen (7) to activate the terminal carbon. Once this process has occurred no other oxygen is required and nitrate can function as the electron acceptor. This helps explain why under strict anaerobic conditions oxidation of the alkanes was limited but under micro-aerophilic conditions considerable oxidation occurred if nitrate was present. One the terminal carbon is modified, various co-oxidations are possible. Some hydrocarbons can be oxidized without the presence of molecular oxygen (9). Other investigators have demonstrated (4,6,8) the cooxidation of non-growth hydrocarbons and the degradation of asphaltenes when n-alkanes are oxidized.

Various microbial products were investigated for their affect on pour point and cloud point. The tests were conducted by placing 10 mL of tap water, 150 mL of oil, and the microbial products into 200 mL sealed serum bottles. Control bottles contained all of the same components without any microorganisms, but did include the carrier materials. Sealed serum bottles were used to create an anaerobic environment. Oil samples from Alberta, Saskatchewan, Utah and Texas were utilized. The pour point tests were conducted according to ASTM-D97 standard methods. These is ± 3ºC accuracy for this type of a test. A reduction of pour point was not established for any of the oils tested. Even though some tests showed reductions these results were not consistently reproducible. The cloud point tests were conducted according to ASTM-D2500 standard methods. A clear yellow high temperature cloud point oil from Utah was selected for these tests. The samples tested showed cloud point depression. The amount of cloud point depression was reproducible, however, a definite trend was established where all samples with bacteria showed some degree of cloud point depression.

Case Histories

There are three organizations in North America wich provide most of the biological paraffin control. It is estimated that approximately 3,000 wells in North America receive regular microbial applications for paraffin control. Like all other approaches to wax control, a 100% success rate is not achievable, however, using proper application techniques a high ratio of success is possible. Three case histories are presented in the following table which illustrate various production conditions.

Location Formation Depth Oil
Production
Water
Production
H2S Microbial
Start Date
Pembian Field Alberta Cardium, Sandston 1,640 M 2 M3/day 7 M3/day nile June 1989
Prior to microbial treatment this well was hot oiled when the operator experienced rods hanging up. This resulted in a hot oil frequency of 2 to 3 months. In December of 1990 (six months after start of microbial treatment) the bottom hole pump was pulled for replacement. The well had not required hot oil treatment since June, 1989. When the pump was changed out a small amount of soft wax was encountered.
Provost Field, Alberta Basal Quartz,Sandstone 890 M 7 M3/day 65 M3/day 3% Oct 1989
Prior to microbial treatment the operator would hot oil the well when he experienced high amperage on his screw pump, indicating increased torque due to excessive wax friction on the rods. This resulted in a 2 to 3 month hot oil cycle. In October of 1990 (one year after start of microbial treatment) the well was pulled to replace the stator and repair a hole in the tubing. No hot oil had been required since treatment started. Only a small amount of soft wax was found on the rods.
Caldwell,
Texas
Austin Chalk 7,500 ft 10 bld 10 bld nil Aug 1990
Prior to microbial treatment the well was hot oiled when the operator experienced excessive rod drag. This resulted in a hot oil frequency of every 1 to 2 wk. The microbial treatments extended hot oil frequency to more than three months.

Literature Cited

  • Broderick, L. S., and J. J. Cooney. 1982. Emulsification of hydrocarbons by bacteria from freshwater ecosystems. Dev. Ind. Microbiol. 23:425-434.
  • Goswami, P., and H. D. Singh. 1991. Different modes of hydrocarbon uptake by two Pseudomonas Species. Biotechnol. Bioeng. 37:1-11.
  • Jobson, A., M. McLaughlin, F. D. Cook, and D. W. S. Westlake. 1974. Effect of amendments on the microbial utilization of oil applied to soil. Appl. Microbiol. 27:166-171.
  • Perry, J. J. 1979. Microbial cooxidation involving hydrocarbons. Microbiol. Rev. 22:686-694.
  • Rambeloarisoa. E., J. F. Rotani. G. Giusti. Z. Duvnjak, and J. C. Bertrand. 1984. Degradation of crude oil by a mixed population of bacteria isolated from sea-surface foams. Mar. Biol. (Berlin) 83:69-81.
  • Rotani, J. F., F. Bosser-Joulak, E. Rambeloarisoa. J. C. Bertrand. G. Giusti, and R. Faure. 1985. Analytical study of Asthart crude oil asphaltenes biodegradation. Chemosphere 14:1413-1422.
  • Singer, M. E., and W. R. Finnerty. 1984. Microbial metabolism of straight-chain alkanes. p. 1-60. In R. M. Atlas (ed.), Petroleum Microbiology. Macmillan Publishing Co., New York.
  • Walker, J. D., R. R. Colwell, and L. Petrakis. 1975. Microbial petroleum biodegradation: application of computerized mass spectrometry. Can. J. Microbiol. 21:1760-1767.
  • Zeyer, J., E. P. Kuhn, and R. P. Schwarzenback. 1986. Rapid microbial mineralilzation of toluene and 1,3-dimethylbenzene in the absence of molecular oxygen. Appl. Environ. Microbiol. 52:944-947.

Web design by Ontra Studios