Metal and hydrocarbon behavior in sediments from ... - Springer Link

Environ Monit Assess (2010) 167:33–47 DOI 10.1007/s10661-010-1516-2

Metal and hydrocarbon behavior in sediments from Brazilian shallow waters drilling activities using nonaqueous drilling fluids (NAFs) Maria do Carmo R. Peralba · Dirce Pozebon · João H. Z. dos Santos · Sandra M. Maia · Tânia M. Pizzolato · Giovani Cioccari · Simone Barrionuevo

Received: 15 December 2009 / Accepted: 19 April 2010 / Published online: 30 May 2010 © Springer Science+Business Media B.V. 2010

Abstract The impact of drilling oil activities in the Brazilian Bonito Field/Campos Basin (Rio de Janeiro) shell drilling (300 m) using nonaqueous fluids (NAFs) was investigated with respect to Al, Fe, Mn, Ba, Co, Pb, Cu, As, Hg, Cr, Ni, Zn, Cd, V, and aliphatic and polynuclear aromatic hydrocarbons concentrations in the sediment. Sampling took place in three different times during approximately 33 months. For the metals Al, As, Co, Cr, Cu, Cd, Fe, Ni, Mn, V, and Zn, no significant variation was observed after drilling activities in most of the stations. However, an increase was found in Ba concentration—due to the drilling activity— without return to the levels found 22 months after

drilling. High Ba contents was already detected prior to well drilling, probably due to drilling activities in other wells nearby. Hydrocarbon contents also suggest previous anthropogenic activities. Aliphatic hydrocarbon contents were in the range usually reported in other drilling sites. The same behavior was observed in the case of polyaromatic hydrocarbons. Nevertheless, the n-alkane concentration increased sharply after drilling, returning almost to predrilling levels 22 months after drilling activities. Keywords Metals · Marine sediment · NAFs · Hydrocarbons · Brazil

Introduction

M. C. R. Peralba (B) · D. Pozebon · J. H. Z. dos Santos · S. M. Maia · T. M. Pizzolato · S. Barrionuevo Instituto de Química, Universidade Federal do Rio Grande do Sul, IQ-UFRGS, Av. Bento Gonçalves 9500, CP. 15003, Porto Alegre, Rio Grande do Sul, 91501.970, Brazil e-mail: [email protected] G. Cioccari PETROBRAS, CENPES, CEGEQ, Av 1 Quadra 07-Cidade Universitária, Ilha do Fundão, Rio de Janeiro, Rio de Janeiro, 21949-900, Brazil

The effect of petroleum drilling and production activities on the environment has been extensively investigated at laboratory research level for more than 35 years. The scope and content of this research have been summarized by several authors including extensive reviews (Kanz and Cravey 1987; Neff 1982). Offshore oil and gas production is a potential source of environmental impacts to the oceans (Rezende et al. 2002). Apart from accidents during operation, prospecting, and drilling, oil fields are of particular environmental significance, since not only oil, but other chemicals, particularly trace metals, may be released

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to the environment during the drilling processes, affecting directly the oceanic biota, which is in general exposed to very low background levels of these substances (Rezende et al. 2002). The activities of petroleum and/or gas drilling, exploration, and extraction have seen a global expansion in recent years (Melton et al. 2000; Rezende et al. 2002; Breurer et al. 2004). New drilling concepts, including horizontal and multilateral wells, have allowed the development of fields with a smaller number of platforms, thus bringing about environmental benefits with the reduction of the affected area (Delvigne 1996). Besides the traditional water-based fluids (WBFs), nonaqueous drilling fluids (NAFs)—whose primary continuous phase is non-water-based, such as low-toxicity mineral oil, refined mineral oil, and synthetic fluids (esters, paraffins, and olefins)— have also been used by the petroleum industry (Delvigne 1996; Melton et al. 2000). These fluids generally are less toxic than the crude-oil-based fluids initially used, due to their lower aromatic compound content and shorter lifetime in the environment. The barite (BaSO4 ) found in NAFs contains metals and metalloids that are considered toxic. Along with other chemical products, barite is a source for the metal and metalloid in drilling fluids. However, the NAF metal and metalloid content may be expected to be similar to that found in WBFs. NAF is constituted of about 46% organic fluid (mineral oil, refined mineral oil, synthetic mineral oil), 33% barite, 18% salt water, 2% emulsifiers, 1% gelificants, and other chemical additives (Melton et al. 2000; Rezende et al. 2002). The impact caused by the drilling activity is mainly due to the presence of fluid and drill cuttings (particles produced when drilling subsurface rocky formations are carried from the bottom of the well to the surface by the drilling fluid). Potential environmental effects from drilling discharges have been a concern of environmental agencies. Residual NAF fluid concentration on the drill cuttings may affect the ecosystem, perhaps by creating changes in microbial activity. In recent work (Pozebon et al. 2009), chemical analyses were conducted on marine bottom sediments collected in deep waters (approximately 2,000 m) before and after the drilling of the wells in order to moni-

Environ Monit Assess (2010) 167:33–47

tor environmental changes from the NAF-based drilling of petroleum wells. The results obtained from that study showed no significant impact from drilling activities for metals and hydrocarbon contents. Giving continuity to that work, the authors are now presenting an investigation about the changes in the aliphatic and polyaromatic hydrocarbon concentrations, as well as those of metals Al, As, Ba, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, V, and Zn in the ocean sediment collected in shallow waters as a consequence of NAF use in the drilling of wells. Therefore, sediment sample cuttings and barite used in the drilling activity were analyzed.

Materials and methods Sampling grid The present study investigates the area surrounding wells BO-22 and BO-23 (Bonito Field), drilled by PETROBRAS (Brazilian Petroleum Company) in Campos Basin (Fig. 1), latitude 22◦ 41 S, longitude 40◦ 37 W, Rio de Janeiro/Brazil. Three cruises (MS 1, MS 2, and MS 3) were carried out for sample collection, in the following periods: predrilling; 3 months, and 22 months after drilling. Three sampling stations in the south and three in the north, 2,500 m away from the well, were labeled as reference stations, due to the fact that the area was expected to be unaffected by drilling activity. For the first cruise, 48 stations in radii of 50, 100, 150, 300, and 500 m were collected. However, between the first (MS 1) and the second (MS 2) cruise, PETROBRAS drilled another well—BO22—located 199 m east of BO-23, and it was not possible to use the same sampling grid in all three cruises. The sampling grid used for the second and third oceanographic cruises (MS 2 and MS 3) was structured with 74 stations in order to contemplate the influence from both wells (Fig. 1). Due to several unexpected factors, such as bad sampling of the collected sample, insufficient sample quantity, excess of water, and changes in the planned activity, not all planned samples were collected. A detailed description of the sampling design is found in Toldo et al. (2010).


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Fig. 1 Sampling grid for sediment sampling stations near wells BO-23 and BO-22, Campos Basin, latitude 22◦ 41 S, longitude 40◦ 37 W, Rio de Janeiro/Brazil. Three sampling stations in the south (ref S) and three in the north (ref N), 2,500 m away from the wells, were labeled as reference stations

Table 1 shows the data related to the three oceanographic cruises (MS 1, MS 2, and MS 3). Sampling A vessel equipped with a Starfix Differential Global Positioning System was used for sediment sample collection. The Hydropro software was used for vessel position and navigation dur-

Table 1 Cruises and respective dates, timing relative to well drilling and sample identification Cruise

Cruise/ name

Date

Timing relative to drilling

1 2

MS 1 MS 2

28–31/07/2001 16–24/09/2002

3

MS 3

16–19/04/2004

Predrilling 3 months after drilling 22 months after drilling

ing all fieldwork. The accuracy of the positioning system was ±1 m. A Sonar Dyne ultrashort baseline (USBL) system was used to accurately determine the position of the box corer [(50 × 50 × 50) cm] and the side-scan sonar. The accuracy of the USBL is ±5 m. The collected sediment samples were frozen and then transported to the Instituto de Química of Universidade Federal do Rio Grande do Sul where they were further analyzed. All materials used for sample collection and storage were properly cleaned in order to avoid contamination. About 200 g of sediment was collected from 0 to 2 cm of depth in the box core. For hydrocarbon analysis, the sediment was transferred to clean glass flasks (250 ml, wide mouth, and Teflon stopper), whereas for metals and arsenic determination separated aliquots were transferred to polyethylene flasks. All samples were kept at 4◦ C.

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Sample analysis Hydrocarbons After defrosting, 30 g of sample dried at room temperature was mixed with 5–10 g anhydrous Na2 SO4 spiked with surrogate analyte (C16 d34 ), purchased from Cambridge Isotopic Laboratories, of known concentration, in order to test the extraction efficiency, and was extracted with dichloromethane (pesticide grade purchased from Mallinkrodt) in a Soxhlet for 12 h using a preextracted cartridge. The extract was concentrated in a rotary evaporator until approximately 1 ml, passed through an activated copper column, concentrated to 1 ml, and fractioned by preparatory liquid chromatography in a silica column to obtain the aliphatic and aromatic fractions following the method proposed by Jafeé et al. (1995). The same procedure was applied to the drilling fluid and cuttings samples. Blank sediment analyses were carried out with 30 g Na2 SO4 (purchased from Merck), previously heated to 400◦ C, spiked with standard surrogate (C16 d34 ), purchased from Cambridge Isotopic Laboratories), of known concentration, and submitted to the same extraction and separation procedures as the samples. Aliphatic hydrocarbons were determined using gas chromatography VARIAN, model 3400, equipped with flame ionization detector, splitless injector, capillary column (30 m × 25 mm × 25 μm) and stationary phase type 5% phenyl dimethylpolysiloxane, with injector temperature of 290◦ C, detector temperature of 300◦ C, column starting temperature of 40◦ C, isotherm for 1 min, heating rate of 6◦ C/min until a final temperature of 290◦ C and isotherm of 20 min. The equipment was calibrated using a mixture of linear aliphatic compounds C8 –C35 and making a linear adjustment of the data produced by injecting five different concentrations of the mixture of each hydrocarbon to be analyzed. The calibration was considered valid when the r2 of the calibration curve was >0.995 for each compound to be analyzed. The response factor (RF) was calculated for each analytical curve, and the RF for each unresolved complex mixture (UCM) was obtained from the mean of the RF values of various compounds eluted in an analysis. The quality control


was made using a standard solution of 5 μg l−1 for every 10 samples determined. For the polyaromatic hydrocarbons, a gas chromatography Agilent (model 6890) with mass detector (model 5390), splitless injector, and a capillary column was used as above. The conditions applied were according to the Environmental Protection Agency (EPA), using the technique of monitoring the selective ion and electron impact at 70 eV for ionization, based on the methodology EPA 625 (EPA-625/SW 8270C). Table 2 presents the compounds monitored and the respective m/z of the molecular ions. The surrogate compounds are presented in italics. The compounds were identified by comparing the retention times and by observing the relative abundance of the respective molecular ions of the components of the samples as compared to the standard surrogates. The calibration curve was obtained using five calibration solutions containing all the compounds described in Table 2. The calibration was considered satisfactory when the relative response factor presented a standard deviation of less than 30%. The analyzing conditions were the same as that was used for aliphatic compounds.

Table 2 Compounds and m/z of the 16 polyaromatic hydrocarbons analyzed by GC/MS Compound

m/z

d8 naphthalene Naphthalene d10 acenaphthene Acenaphthylene Acenaphthene Fluorene d10 fenantren Fenantren Anthracene Fluoranthene Pyrene Benz(a)anthracene Chrysene d12 perylene Benz(k)fluoranthene Benzo(a)pyrene benzo(ghi)perylene Indeno(123-cd)pyrene Dibenzo(ah)anthracene Benzo(b)fluoranthene

136 128 164 152 154 166 188 178 178 202 202 228 228 264 252 252 276 276 278 252


The quantitative analysis was internal standardization, adding to the aromatic fraction known concentrations of perdeuterated surrogate naphthalene, acenaphthalene, phenanthrene, chrysene, and perylene, and the quality control was performed using calibration solutions of 5 μg l−1 (ppb) applied together after every 10 sample analyzed. All analyses were carried out in triplicate. Metal and arsenic determination The frozen sediment samples were removed from freezer, dried at room temperature—in clean environment—and then sieved through a 2-mm nylon sieve. The retained material was discarded. Subsequently, the sieved sediment samples were ground in agate mortar, down to