Treatment of Oil Contaminated Drilling Waste Using Supercritical Fluid Extraction with Carbon Dioxide
Christianne Street* and Selma Guigard
Department of Civil and Environmental Engineering
University of Alberta,
Edmonton, Canada, T6G 2W2
*Corresponding author. Tel.:(780)492-9094, email:
C. Street/S. Guigard01/25/06
Treatment of Oil Contaminated Drilling Waste Using Supercritical Fluid Extraction with Carbon Dioxide
ABSTRACT
In the process of drilling for oil and gas, drilling muds are used to lubricate the drilling equipment and return the rock cuttings to the surface. This spent mud, or drilling waste, is generated in large volumes and cannot be released to the environment without further treatment. The muds are composed generally of powdered barite in a fluid base. Hydrocarbon based muds are technically superior due to their inherent lubricity. While they are preferred over water-based muds, especially in challenging drill operations, their environmental toxicity inhibits their use. There are many technologies to treat drilling wastes but most are costly or not effective at meeting strict environmental regulations. One example of an innovative technology to solve these problems is supercritical fluid extraction, an extraction technique that uses substances at elevated temperature and pressure as solvents to effectively remove hydrocarbons from solid matrices.Carbon dioxide is often selected as the solvent in these applications because it is inexpensive, readily available, non-flammable and environmentally friendly.
Previous studiesundertaken at the University of Alberta in the Department of Civil and Environmental Engineering have investigated the use of carbon dioxide as a solvent for the removal of natural oil from drilling waste. These studies have shown that carbon dioxide at or aboveits thermodynamic critical point of 303.15 K and 7.4 MPa is capable of removing up to 98% of the hydrocarbon from the waste (López Gómez, 2004; Odusanya, 2003)This brings the hydrocarbon content of the waste to below Canadian regulatory levels for environmental release.
Using gas chromatography, the extracted hydrocarbons were also confirmed to be similar in composition to those originally present in the drilling waste.
In the current study, centrifuge underflow drilling waste containing synthetic oil will be placed in a pressure vessel and mixed in the presence of supercritical carbon dioxide under the optimum conditions as indicated in López Gómez (2004) and Odusanya (2003). The carbon dioxide/hydrocarbon solution will then be passed through a depressurization device where the carbon dioxide will be vented and the hydrocarbons will be precipitated and collected in vials.Soxhlet extraction and gas chromatography/flame ionization will be used to determine the hydrocarbon content of the waste before and after the process.
A one-factor-at-a-time approach will be taken to optimize the extraction process for the synthetic oil based waste. Results are expected to be similar to those obtained in the previous studies. Data collected willbe compared to indicate possible differences between the hydrocarbon recovery of the system on drilling waste based in synthetic and natural oil.
While these studies have been carried out in lab-scale, it is hoped that the knowledge gained will lead to the eventual commercial development of this environmentally sound technology. Economically, the treatment of drilling waste using supercritical fluid extraction would also allow the recovery and reuse of expensive hydrocarbon based drilling fluids. Effective application of the supercritical fluid extraction process would allow the drilling industry to use technically superior hydrocarbon based muds without the burden of their high cost of use, treatment and disposal.
REFERENCES
López Gómez, J. J. 2004. The Use of Supercritical Fluid Extraction for the Treatment of Oil Contaminated Drilling Waste. M.Sc. Thesis, Department of Civil and Environmental Engineering, University of Alberta, Edmonton, AB.Due to confidential results, this thesis is currently not available.
Odusanya, O. O. 2003. Supercritical Carbon Dioxide Treatment of Oil Contaminated Drill Cuttings. M.Sc. Thesis, Department of Civil and Environmental Engineering, University of Alberta, Edmonton, AB.
KEY WORDS
supercritical fluid, carbon dioxide, non-aqueous based drilling waste, synthetic drilling waste
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