During the last years, a complete set of brines, groundwaters and surficial waters surveys was carried out in oilfields in order to determine the presumed oil born contribution to the groundwater pollution. The survey included the most important basins in Argentina and a wide variety of geological and hydrogeological conditions. Although conventional hydrogeochemistry played an initial role, the isotope tool has been the key for unravelling some delicate and doubtful cases. Most brines are very well characterized by their isotope composition and high salinity, leading to an easy recognition in the case of mixing. Besides the stable isotope composition of oxygen and hydrogen, tritium and Sr isotopes helped to model the interaction of production waters, groundwaters and surficial waters. As a matter of fact, and except for some old passives, the results showed that the improvement and change in water managing practices during the last decade avoided major problems. Despite this situation, the lack of knowledge on the new practices of oil industry and a high degree of incredulity from the people, limits the appreciation of this improvement to the courts and specialists. A thoroughful campaign to clarify the results, utility, confidence and limits of a multitracer approach is necessary to face the public concern in order to demonstrate that the oil activity can be environmentally friendly and that the water resources are a common heritage that will be preserved. Introduction From the beginning of oil exploitation in Argentina, several environmental accidents have been pointed out. Towards the 90's, the rise of public concern on the environment and the possibility of litigation from landowners, NGO and government agencies caused a change in the treatment of oil industry pollution. The oil companies faced with trials, demands and discredit due bad antique environmental practices and the lack of responsibility of some oilfield operators. Since the 90's, the improvement on spill and waste management, environmentally friendly technologies and a focus on best practices were the norm in the oil industry. However, many passive exist even today and some of them are being object of remediation. One of the most critical matters is the existence of groundwater contamination related with infiltration ponds, secondary recovery projects and spills. Although there were many cases in the past, nowadays the strict control policies limit the possibility of casual or deliberate "production water" mixing with surficial waters or groundwaters. However, the existence of groundwater contamination due past practices has been object of debate. Many landowners from arid regions feel that the oil companies have contaminated their water resources and that they are paying the mistakes from decades ago, starting a legal battle claiming for their rights and the oil companies' liablility. As a consequence, a battery of studies was done in critical areas to constrain and evaluate the problem. Objectives The aim of this contribution is to present groundwater studies from suspected contaminated sites in Argentina, showing some results in order to demonstrate that it is possible to constrain the real responsibilities, even in cases were could have been accepted and approved bad practices. Some suggestions to improve environmental performance and clarify related issues are also presented.
Organic geochemistry has been widely used in oil exploration industry. However, only in the last decades, innovative applications of its methods have become known in field development activities and reservoir characterization. One powerful application is the lateral and vertical fluids continuity in reservoirs. This study was made in Chihuido de la Sierra Negra-Lomita field, Neuquina Basin, which produces from three main reservoirs: Low Troncoso Formation, Avilé Formation and Rayoso Formation. In the mature stage of field development, RepsolYpf developed an analytical technique based in organic geochemistry to discriminate the production from each reservoir in commingle produced oil samples. The goal of the present paper is the integration of the geochemistry results and the geological model of the Rayoso Formation in order to establish the lateral and vertical continuity of the reservoir fluids, seal rock quality variations and support the field developments activities. According to the obtained results, the following conclusions were reached:Rayoso Formation produces oils with different geochemistry characteristics andThe geochemical characterizations of the oils produced in Rayoso Formation is going to be used as a powerful supporting technique for field development. Introduction Organic geochemistry has been widely used in oil exploration industry like source rocks identification, source rocks maturity evolution, estimation of hydrocarbon volumes generated by the same ones and the source rocks and oils geochemical characterization to establish petroleum and petroleum - source rocks correlations. From 1985 several examples of applications of organic geochemistry to help the resolution of production and reservoir problems were published in different specialized bibliography 1–6. The main difference between an exploration and a reservoir/production studies is the sampling scale. In the regional studies, petroleum and source rock samples are selected according to the different petroleum systems, managing to determine the genetic tendencies of maturity and relationship between petroleum and source rocks. In reservoir and production studies, a detailed sampling of producing layers is made. One of the most surprising observations of reservoir geochemistry is that all the fluids (water, gas, petroleum) are heterogeneous in composition as much in vertical as lateral direction. Therefore, the analysis of these heterogeneities allows characterizing individual layers and helps to allocate the production. The quality of the fluids present in the analyzed levels can be determined by means of this study and lateral and vertical correlations of them can be established. This information allows to determine the trap filling mechanisms, to establish the processes of alteration undergone by the fluids in the reservoirs or during the migration and, by means of integration with the geologic model, can be understood the interrelation of the reservoir architecture with the dynamics of the fluids. This information allows establishing a fluid distribution model on independent data from the geologic information since it is a direct determination on the fluid and it does not require previous calibration. The fluid distribution in reservoir can help to a better understanding of the reservoir behavior. The present article shows the characterization of petroleum produced from Rayoso Formation reservoir and their integration with the geological model of Chihuido de la Sierra Negra-Lomita field (Fig. 1). The goal is to establish the lateral and vertical continuity of the reservoir fluids, seal rock quality variations and support the field developments activities.
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