Redox reactions in hydrocarbon clastic reservoirs: experimental validation of this mechanism for porosity enhancement

Abstract

Oil-rock-water reactions in hydrocarbon reservoirs were evaluated experimentally. Hematitic Tensleep Sandstone samples of 10–20 cm 3 were heated with 200 ml of deionized water and 100 ml of petroleum for 3–14 days at 200–360°C. The Tensleep Sandstone samples are mature quartz arenites with 5–25% carbonate matrix and cement and minor amount of anhydrite pore-fillings. Results indicate that significant potential exists for redox reactions between oxidized mineral phases and crude oil. Iron oxides (± sulfate) were reduced and hydrocarbons were oxidized to oxygenated organic compounds (such as CO 2 and organic acids). Organic acids generated during the redox reactions partitioned into the system water, dissolving framework grains and cements (primarily carbonates). Original porosity of the samples ranged from 6% to 15%, and increased by ∼ 13–20%, to 7–18%, or more after experimentation. As reactions between hydrocarbons and mineral oxidants proceed, redox reactions occur, under increasingly reducing condition as temperature increases, and result in enhanced sandstone reservoir porosity.