Abstract
Acid stimulation may cause formation damage due to incompatibility of the injected acid and crude oil, which may form stable emulsion and ultimately acid sludge. In this process, the pH value of the injected live HCl solution increases during reaction with rocks or minerals. The spent acid may, in turn, be incompatible with the reservoir fluid causing formation damage. Due to the prevalent drawbacks of these unwanted emulsions, this study focused on the stability of spent acid-crude oil emulsions affected by pH, ferric ion concentration and acid to mixture volume ratio (AMR) through a series of systematic experiments. Response surface method (RSM) was applied for design of experiments and using crude oil samples with various properties, which helped to get better insight into acid-crude oil interactions. The results showed that crude oil properties, such as TBN, aromaticity, asphaltene to resin ratio and CII, affect the emulsion stability. A crude oil with higher TBN, CII and asphaltene to resin ratio, and lower aromaticity, has more affinity to interact with the spent acid and to form stable emulsion. The pH value of the spent acid was of lower importance than other properties as stated above, while AMR was found to be the most influential factor in such a way that it reversely influenced the emulsion stability. The impact of ferric ion depended on both pH of the spent acid and chemical properties of the crude oil. Based on the microscopic images of the emulsion droplets, it was concluded that the stability of spent acid-crude oil emulsion is closely associated to characteristics of the interfacial film than the droplet size.
Published Version
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