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Oil Cleanup Case Study at the RMOTC

 

Case Study at the Rocky Mountain Oilfield Testing Center

Aqua Technologies and RMOTC conducted a 24-hour test at the US Naval Petroleum Reserve #3 (Teapot Dome oil field) on July 11- 12, 1996. The general intent of the test was to evaluate the ability of ET-1 to adsorb hydrocarbons from produced water. While the ability of ET-1 to adsorb oil spills and hydrocarbons has been proven in the laboratory and in other applications, it was not known if the product would perform as expected in a field environment where waters carry a free oil sheen and where there are wide variations in hydrocarbon concentrations. It was also unknown whether it would perform well enough to reduce BTEX below RCRA contaminant levels. A 24-hour test was deemed long enough to accomplish the goals of the test.

Crude oil and associated water at NPR-3 are produced from the Tensleep formation, one of several Pennsylvanian - Permian formations that contribute most of the produced water that is discharged within Wyoming. Other formations that produce water capable of being discharged include the Minnelusa and the Phosphoria. NPDES discharge limits and chemical composition are presented in tables 1 and 2.

One early complication of the field test was that the temperature of the water was higher than the maximum operating temperature of ET-1. Tensleep wells are pumped using high volume submersible electric pumps, bringing water and oil to the surface at nearly 200 F. Polymer loss from ET-1 becomes excessive above about 150 F, thus for testing purposes, Tensleep water was transferred from the usual holding tank to a portable storage tank two days before the test. This allowed the produced water to cool to approximately 95 F before the test began. The tank was agitated immediately prior to the test in order to disperse any crude oil that may have separated. Aqua Technologies test trailer consisted of the following equipment:

  • An electric transfer pump rated for approximately 5 gallons per minute.
  • A 0-10 GPM flow meter.
  • Two 55-gallon drums containing ET-1.
  • One 55-gallon drum containing Granular Activated Carbon (GAC).
  • Sample points for obtaining desired water samples.

The drums were purchased from Tetrasolv, Inc. and include a spreader system and all the necessary inlet and outlet fittings. The equipment was installed so that water flowed upward from the bottom in drums containing ET-1, but downward through the GAC. This was done in order to avoid fluidizing the GAC and causing channeling through the media. The specific equipment used in the test operates at a maximum rate of 10 gpm, maximum temperature of 100 F, and at a maximum pressure of 10 psi.

Before the start of the test, the system was purged of air and filled one vessel at a time until the unit was completely filled with water. Aqua Technologies staff decided that there was no need for the system to reach dynamic equilibrium before sampling, so the transfer pump was started and the first sample was taken shortly thereafter.

Sampling

Samples were taken according to written procedures and EPA protocols to ensure the reliability of the analytical results. Procedures included the use of precleaned and sealed glassware, obtaining zero-headspace samples when necessary, chilling the samples to 4 C for storage and transportation, and delivery to a commercial lab within published holding times. Four sets of samples (numbered 1-4) were obtained during the 24-hour test. Each set contained one upstream sample (sample A,), one sample taken between the second ET-1 container and the drum containing GAC (sample B), and one downstream sample (sample C). In this manner, one can compare contaminant concentrations across the process or look at a specific sample location over time. Samples were analyzed for Total Petroleum Hydrocarbons (TPH - EPA method 418.1, see table 3), Oil & Grease (EPA Method 413.2, see table 4), and BTEX (EPA Method 8020, tables 4-8). These analyses were believed to be the ones most interesting to industry due to their frequent use as regulatory parameters.

Test Results

The results of laboratory analyses are shown in tables 4-8. After review of the test chronology and lab data, RMOTC and Aqua Technologies were able to conclude that the combination of ET-1 and granular activated carbon consistently and effectively removed hydrocarbons from produced water. Specific findings are that ET-1:

  • Reduced Total Petroleum Hydrocarbons to non-detectable levels. In all four sets of samples, TPH was below detectable limits after adsorption by ET-1 alone (sample B).
  • Reduced Oil and Grease to non-detectable levels. In three of four samples, Oil and Grease was below detectable limits after adsorption by ET-1 alone (sample B). The fourth sample detected Oil and Grease at the detection limit of 1.0 mg/l.
  • Reduced soluble hydrocarbons: Benzene, Ethylbenzene, Toluene, and Xylene to barely detectable levels. In all four sets of samples, BTEX was barely detectable after adsorption by ET-1 alone (sample B). BTEX was below detectable limits after the combination of ET-1 and granular activated carbon (sample C).

In simple terms, ET-1 eliminated hydrocarbon contamination from produced water during the test. Other testing conducted by Aqua Technologies has shown that similar results are possible in large-scale commercial applications.

Upstream Oil and Grease concentrations are higher during this test than normally encountered during NPDES sampling. The reasons for this are unknown, but it is possible that the frac tank or water truck used to haul the produced water contained additional
oil beyond the amount contained in the produced water. Regardless, the test conditions represent a difficult case for treatment, having both high concentrations and wide variations in hydrocarbon content.

 

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