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Effects of various chemical agents on wettability of oil-wet carbonate rocks

UDK: 622.
Key words: wettability, imbibition, chemical agents, Amott-Harvey index, contact angle
Authors: O.S. Sotnikov, M.M. Remeev, D.V. Nuriev, M.R. Khisametdinov, K.M. Musin (TatNIPIneft, RF, Bugulma), R.K. Khairtdinov (Enterprise Kara Altyn ZAO, RF, Almetyevsk)
Results of the analysis of Bashkirian core samples from the Akanskoye field suggest that these rocks are preferentially oil-wet. This interferes with the technical success of waterflood projects. It is believed that displacement efficiency in preferentially oil-wet reservoirs may be improved through wettability alteration and reduction of oil - injectant interfacial tension. The experimental research was aimed at identifying the most efficient chemical agent capable of changing the original wettability of oil-wet rocks. The research comprised two stages. At the first stage, three most promising chemical agents were selected for the production target. For various concentrations of these chemicals, contact angles and interfacial tension in the oil-aqueous chemical solution system were determined. As a result, chemical agents capable of minimizing interfacial tension and contact angle were recommended as well as optimal concentrations thereof. The second stage consisted in Amott wettability tests on the Bashkirian core sample from the Akanskoye field using the recommended chemicals. In accordance with experimental research findings, the most efficient compositions in terms of wettability alteration are 0.5% water-soluble nonionic surfactant with 2% ethylene glycol and 0.5% water-soluble complex surfactant system in formation water. Increase in concentrations of the above surfactants from 0.5 to 1% does not facilitate changes in Amott – Harvey wettability index. Addition of 2% ethylene glycol to 0.5%- and 1% water-soluble nonionic surfactant solution in formation water brings about more substantial wettability changes to water-wet conditions compared to original surfactant solutions.
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