ORGANIC-ACIDS AND INORGANIC-IONS IN WATERS FROM PETROLEUM RESERVOIRS, NORWEGIAN CONTINENTAL-SHELF - A MULTIVARIATE STATISTICAL-ANALYSIS AND COMPARISON WITH AMERICAN RESERVOIR FORMATION WATERS

A data base consisting of organic acid anion composition, reservoir depth, temperature and pressure, and inorganic ion composition of 22 samples of produced formation waters from different wells on the Norwegian continental shelf is presented. Correlation between the different properties of the samples was explored by multivariate statistical analysis, with special emphasis on the organic acid concentrations. Organic acid concentrations, pH and alkalinity are positively correlated with each other and in general negatively correlated with the inorganic ion concentrations. No significant correlation was found between organic acid levels and reservoir temperature. Alkalinity values can be predicted from the remaining ionic composition of the samples with reasonable accuracy, while surface-measured pH cannot be accurately predicted. A comparable statistical analysis was performed on an American formation water data set. These waters separate into statistically different classes based on reservoir types. Strong similarities are found for the oil reservoir waters in the two data sets.