Model for the origin of carboxylic acids in basinal brines

Carboxylic acids are ubiquitous in basinal brines from petroleum-producing sedimentary basins. Although the absolute concentrations of individual shor t-chain acids vary systematically over many orders of magnitude, relative a bundances are characterized by approximately constant ratios. Laboratory ex periments have demonstrated that oxidation of aqueous n-alkanes proceeds th rough a sequence of reactions involving alkene, alcohol, ketone, and carbox ylic acid reaction intermediaries. The highly specific nature of these reac tions allows the relative distribution of carboxylic acids produced during oxidation of n-alkanes to be predicted quantitatively as a function of petr oleum composition. A model based on the results of laboratory experiments w as developed to account for the thermogenic production of aqueous carboxyli c acids in sedimentary basins. Model predictions are highly consistent with the distribution of carboxylic acids observed in nature. This result suggests that hydrocarbon oxidation reactions may be pervasive during petroleum maturation in sedimentary basin s. Likely oxidizing agents include ferric iron-bearing aluminosilicates, ox ides, and hydroxides, pyrite, sulfate-bearing minerals, and water. Such che mical interactions allow inorganic sedimentary components to act as sources of oxygen for the formation of oxygenated organic alteration products. Acc ordingly, the absolute amount and timing of carboxylic acid generation may not be limited by the compositional evolution of kerogen, as suggested by p revious models. Copyright (C) 2001 Elsevier Science Ltd.