Abstract
Water-based enhanced oil recovery (EOR) from carbonates is usually restricted by initial wetting properties, especially in naturally fractured carbonates. Carboxylic material in the crude oil, quantified by the acid number (AN), is regarded as the most important wetting parameter. In this paper, it is shown experimentally that, for a given AN, the temperature and the amount of sulfate present in the formation water will affect the wetting condition significantly. The concentration of sulfate in the formation water is usually low because of a high amount of Ca2+, anhydrite, CaSO4(s), is precipitated at high temperatures. The interaction between small amounts of sulfate dissolved in the formation water and the rock surface was studied using chalk cores. The relative amount of sulfate dissolved in the pore water, SO42–(aq), and sulfate adsorbed onto the chalk surface, SO42–(ad), was quantified at different temperatures of 20, 50, 90, and 130 °C. Below 50 °C, the relative amount of SO42–(aq) and SO42–(ad) was...
Published Version
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