The role of exogenous oxygen in organic acid generation in deep reservoirs of petroleum-producing basins: Progress and prospects

Abstract

The source, yield, and distribution of organic acids in oilfield waters in petroleum-producing basins have not been satisfactorily explained by previous studies that have focused on oxygen-containing functional groups in kerogen as the major source of such acids. This study reviews four possible mechanisms by which exogenous oxygen can participate in petroleum or organic acid generation. Biodegradation and mineral oxidation generate organic acids in oilfield waters, leading to an increase in the oxygen content of altered oils, which then have greater potential for producing organic acids. Hydrolytic disproportionation reaction and thermochemical sulfate reduction reactions at high temperatures lead to the in situ generation and accumulation of organic acids in deep reservoirs. The incorporation of exogenous oxygen increases the yield and expands the distribution of organic acids in reservoirs at various depths. The acids derived from exogeneous oxygen play critical roles in the development and preservation of deep reservoirs. Further research is required to determine the volumes and compositions of organic acids produced by these reactions, and to further understand the role of organic acids in the alteration of deep reservoirs under more realistic conditions.