Publication Date:
2005-08-01
Description:
This article presents the first results of chlorine residual salt analysis (Cl-RSA), a new technique that allows investigation of the isotopic composition of chlorine in oil-field waters from core analysis. As water evaporates, the residual salts precipitate in the pores of a core. Unlike the routinely used strontium isotope residual salt analysis (Sr-RSA) technique, which determines the composition of a trace element (strontium), the Cl-RSA technique allows the determination of the isotopic composition and origin of one of the most abundant anions in natural waters. The results show that combining the δ37Cl of two successive leachates of a core sample leads to an isotopic composition that is representative of pore water. The reproducibility of the method applied to sandstone samples is considered to be ±0.05‰. The Cl-RSA technique was tested on two wells from the Elgin area (North Sea, United Kingdom). The δ37Cl results in formation waters range from −1.03 to −0.57‰, with an overall increase with depth. These results have been compared to the 87Sr/86Sr ratios of pore waters determined in the same wells using the Sr-RSA technique. The similarity of form between the δ37Cl and 87Sr/86Sr profiles with depth confirms that residual salts permit a reliable investigation of the chlorine isotopic composition from core analysis. As with the Sr-RSA technique, Cl-RSA could be used to test the isotopic homogeneity of a sample and to assess the compartmentalization of oil fields and reservoirs. This technique could provide key information regarding the origin of the salinity and its evolution during the reservoirs' filling, as well as help in the monitoring during field production. Véronique Woulé Ebongué is a Ph.D. student in the Stable Isotope Laboratory of the Institut de Physique du Globe de Paris (France). Her field of research is the application of the isotopic geochemistry of chlorine to fluid circulation in sedimentary basin and oil fields. Nathalie Jendrzejewski, Frédéric Walgenwitz, and Françoise Pineau are her Ph.D. advisors.Nathalie Jendrzejewski is a senior research fellow in the Institut de Physique du Globe de Paris (IPGP). After a Ph.D. in geochemistry (1994), she joined the IPGP Laboratoire de Geochimie des Isotopes Stables in 1996. Her research focuses on the geochemistry of chlorine using its stable isotopes. Her main application areas include volcano survey, magma degassing, fluid circulation, and pollution characterization. Frédérick Walgenwitz obtained his Ph.D. in 1976 from the University of Besançon (France), and he joined Elf Exploration and Production in 1977. He is now working with Total in Pau (France) and is an expert in diagenesis and inorganic geochemistry applied to the study of reservoirs and oil-field waters. Françoise Pineau was has been director of research in Centre National de la Recherche Scientifique at the Laboratoire de Géochimie des Isotopes Stables (Université of Paris 7 and the Institut de Physique du Globe de Paris) since 1969. Her main interests focus on the geodynamical cycles of C, H, N, and O and the origin of the isotopic variability of materials like carbonatites, peridotites, basalts, and deep continental crust (granulite facies) within the Earth's mantle. Marc Javoy is professor at University Denis Diderot and at the Institut de Physique du Globe de Paris, where he developed the Stable Isotope Laboratory. He was chairman of the Laboratoire de Physico-Chimie des Fluides Géologiques of the Centre National de la Recherche Scientifique–Institut de Physique du Globe de Paris–University of Paris 7. His present main areas of research are the geodynamical cycles of volatile elements and the problems of the Earth's formation.
Print ISSN:
0149-1423
Electronic ISSN:
1943-2674
Topics:
Geosciences
Permalink