Efluentes de 66 plataformas de produção de petróleo e gás natural, Bacia de Campos/Brasil: monitoramento, diagnóstico e avaliação de tendências

Abstract

Oil and gas production activities generate effluents with significant potential to cause environmental impacts. Considering the increase in the number of areas to perform these activities in Brazil, the present study aimed to contribute with a detailed diagnosis of the quality of effluents discarded by offshore platforms in the Campos Basin, evaluating patterns and trends. The study was based on environmental monitoring reports of produced water, oily waters and effluents from the injection system, referring to 66 offshore platforms of the Campos Basin, in the period from 2012 to 2016. The produced water was the effluent discarded by most of the platforms and the one of greater volume of discard in the sea. Although there is a threshold value for the concentration of oil and grease (TOG) in the effluents, a load of 695 to 942 tons of TOG have been released into the sea together with production waters discharged during the period. The volume of injection system effluent increased during the period, indicating that greater attention is needed in its management, mainly because this effluent has no threshold value for disposal, and it contains substances acting as biocides, incrustation inhibitors and membrane cleaners. The records and reports of oily water discharged were irregular indicating the need for improvements in the management. Trend analyzes showed the increase in volume and the pollutant load of the production water. Descriptive statistics of production water indicated great variability in the concentrations of chemical and toxicity, which are monitored according to CONAMA Resolution 393/2007. In general, the produced water presented concentrations for chemical variables compatible with this type of effluent and with values coming from other oil producing regions. However, in terms of median values, it was observed higher concentrations of barium, radio-226 and radio- radio-228, in addition to the increased toxicity associated with the studied samples, when compared to a previous study conducted with production water in Brazil. Principal component analysis (PCA) and analysis of correlations between production water toxicity (expressed by the Concentration of Non-Observed Effect-CENO) and chemical variables indicate that BTEX, naphthalene, phenanthrene, radioisotopes and salinity were the variables more important to describe the chemical composition of the produced water, both in terms of concentrations and in terms of association with toxicity. In this sense, the correlations between ecotoxicity (CENO) and chemical variables indicated that less than 10% of the variability in terms of produced water toxicity is explained by these monitored chemical variables. A comparative study between different treatment systems used in the Campos Basin suggested that the use of filters practiced by a few platforms reduced significantly (p <0.05) the concentration of chemical variables in the production water as well as the ecotoxicity of this effluent and filtering is therefore recommended. The results indicate that offshore platform effluent management can be improved, with better records of volumes and pollutant loads. Additional recommendations include: replacement of the TOG quantification method; installation of filters in the treatment systems and; an evaluation of the contribution of substances such as biocides, incrustation inhibitors and membrane cleaners to the final effluents ecotoxicity.