Elsevier

Microchemical Journal

Volume 85, Issue 2, April 2007, Pages 234-238
Microchemical Journal

Analysis of BTEX, PAHs and metals in the oilfield produced water in the State of Sergipe, Brazil

https://doi.org/10.1016/j.microc.2006.06.002Get rights and content

Abstract

During oil and gas exploitation, large amounts of produced water are generated. This water has to be analyzed with relation to the chemical composition to deduce the environmental impact of its discharge after a treatment process. Therefore, a study was carried out to evaluate preliminarily the BTEX (benzene, toluene, ethylbenzene and xylenes), polycyclic aromatic hydrocarbons (PAHs) and metals contents in produced water samples taken from effluents of the Bonsucesso treatment plant located in the city of Carmópolis, the most important oil and gas producer in the State of Sergipe, North-east of Brazil. Three methods were optimized to determine the target compounds. Polycyclic aromatic hydrocarbons were determined by gas chromatography with mass spectrometric detection (GC/MS), volatile aromatic hydrocarbons (BTEX) by gas chromatography with photoionization detector (GC/PID) and metals were analyzed by flame atomic absorption spectrometry (FAAS). The results showed that concentrations of the target compounds in these samples ranged from 96.7 to 1397 μg L 1 for BTEX, from 0.9 to 10.3 μg L 1 for PAHs and from 0.003 to 4540 mg L 1 for metals.

Introduction

Petroleum exploitation began 1961 in the State of Sergipe in the city of Riachuelo, with activities of which extended rapidly to other regions. The State of Sergipe is the third biggest petroleum producer in the Northeast region of Brazil. This activity is very important to the local economy, being responsible for 40% of gross regional domestic product. Today, petroleum production is undertaken in both onshore and offshore operations [1]. Petroleum exploration and production in the Sergipe/Alagoas region produces approximately 8500 m3 of crude oil per day, 5000 m3 of natural gas per day and 33,000 m3 of water per day. Approximately 85% of this produced water is extracted in the terrestrial platforms and is sent to the Bonsucesso treatment plant located in the city of Carmópolis. The State of Sergipe is Brazil's largest terrestrial petroleum production field and the fourth biggest producer in the world, with an estimated production of 3600 m3 of crude oil per day and 28000 m3 of water per day. A part of this water is re-injected into wells to extend the production lifetime of the oilfield and the rest used to dissolve salts generated by the Vale do Rio Doce Company, being subsequently discharged to subsurface waters after treatment.

The production of oil and gas is usually accompanied by the production of water. This produced water consists of formation water, which is water naturally present in the reservoir, floodwater previously injected into the formation and condensed water, as a result of gas production [2]. Hence, produced water is a by-product of the oil and gas exploitation and production processes in terrestrial or offshore platforms. Large volumes of this produced water are often generated because many oil deposits reside in or around groundwater aquifers [3]. During the lifetime of the oilfield, the amount of water may range from seven to ten times the amount of oil produced [4]. The chemical composition of this wastewater is dependent upon the geological formation. It may contain various toxic compounds of natural origin such as volatile aromatic fractions of the oil, including BTEX, polycyclic aromatic hydrocarbons (PAHs), organic acids, phenols and alkylated phenols, metals, radionuclides and a very high salt concentration.

Some studies have been described in the literature on chemical characterization of produced water from offshore oilfield platforms in China, Norway, Austria and the United States [5], [6], [7], [8], [9], [10]. In Brazil, limited monitoring has been carried out on naturally-occurring compounds such as organic acids, phenols, metals, PAHs and BTEX in produced water. Among them, there are studies on the evaluation of different technologies for oilfield wastewater treatments from the Campos Basin, State of Rio de Janeiro [11], [12]. However, there is a general lack of data on the chemical composition of produced water from oilfields in the State of Sergipe. The chemical composition of produced water is field-dependent. So, the field-specific detailed chemical characterization of produced water from each oilfield or platform is necessary in order to predict the fate and effects of the produced water discharged to the environment.

Taking into account the above considerations and considering that, to date, no data on chemical composition of the oilfield produced water in the State of Sergipe have been reported in the literature, this paper provides a preliminary evaluation of the levels of BTEX, PAHs and metals in the effluent of produced water from the Bonsucesso treatment plant located in the city of Carmopólis, State of Sergipe. This treatment station receives produced water from a number of different petroleum production units.

Section snippets

Chemicals and materials

Dichloromethane, acetonitrile and n-hexane were nanograde (Mallinckrodt Baker, Paris, KY, USA). Certified standards of BTEX (benzene, toluene, ethylbenzene and m-xylene, o-xylene and p-xylene) were purchased from ChemService at concentration of 2000 μg mL 1 in methanol (West Chest, PA, USA). Intermediate solutions were prepared by diluting the standard mixture at concentrations of 5 and 50 μg mL 1 in methanol. The deionized water used for preparing working solutions was purified by a Millipore

General comments

This study reports on results obtained from a survey of wastewater from the Bonsucesso produced water treatment plant for the levels of BTEX, PAHs and metals in the effluent. This treatment plant was selected because it contributes a high percentage of the total amount of produced water discharged into subsurface waters from the oilfields of the State of Sergipe.

BTEX analysis

The above described extraction procedure was developed on the basis of EPA method 524.2 (purgeable organic compounds by the PT

Conclusions

This paper describes the evaluation of PT-GC/PID, GC–MS and FAAS for the determination of BTEX, polycyclic aromatic hydrocarbons and metals of environmental interest, respectively, in produced water samples. The reliability and performance of the analytical methods were checked by determining the detection and quantification limits, precision and accuracy. Concentration levels ranged from 96.7 to 1397 μg L 1 for BTEX, from 0.9 to 10.3 μg L 1 for PAHs and from 0.003 to 4540 mg L 1 for metals, in

Acknowledgements

The authors gratefully acknowledge Dr. Andrew Allen (University of Birmingham) for his assistance with the English in this manuscript and the Petrobras/Unseal, CNPq/PIBIC, FAPITEC-SE/FUNTEC and the FINEP for financial support of this study. We also would like to thank the Bonsucesso treatment station located in the city of Carmópolis, State of Sergipe, for the produced water samples.

References (21)

  • L. Washburn et al.

    Cont. Shelf Res.

    (1999)
  • L.G. Faksness et al.

    Mar. Pollut. Bull.

    (2004)
  • G.T. Tellez et al.

    Microchem. J.

    (2005)
  • R. Kadnar

    J. Chromatogr., A

    (1998)
  • T. Sirivedhin et al.

    Chemosphere

    (2004)
  • J. Lu et al.

    Chemosphere

    (2006)
  • J.C. Campos et al.

    Water Res.

    (2002)
  • C.M. Reddy et al.

    Mar. Pollut. Bull.

    (1999)
  • R.M.R. Fonseca, A importância do aproveitamento da água resultante da produção de petróleo. Monograph, UFS, São...
  • S.F.J. Vegueira et al.

    J. Environ. Radioact.

    (2002)
There are more references available in the full text version of this article.

Cited by (114)

View all citing articles on Scopus
View full text