Preflush design for oil-wet carbonate formations: Key to enhance scale-inhibitor-squeeze lifetime

Scale-inhibitor-squeeze lifetime is measured by the duration for which the scale-inhibiting chemical is released at a concentration greater than the required minimum inhibitor concentration (MIC). Hence, enhancing scale-inhibitor adsorption and storage may proportionately enhance squeeze lifetime. With most oilfield squeeze scale inhibitors being aqueous-based, they are unlikely to be adsorbed on an oil-wet formation in optimal quantity. Investigations are made in this research on how to create the appropriate formation condition so that adsorption and lifespan of scale inhibitor in an oil-wet carbonate reservoir are enhanced, focusing on preflush design (formation-conditioning stage). Surfactants (of anionic and non-ionic type), a cosurfactant, and alkali are deployed and results are evaluated through interfacial tension (IFT), phase-behavior analysis, coreflood studies, and inductively coupled plasma-mass spec-troscopy (ICP-MS) analysis. Flow experiments are conducted in simulated reservoir condition by use of data and materials from a high-temperature and high-salinity carbonate reservoir. The results reveal that nonionic surfactant is most favorable in terms of scale-inhibitor-squeeze lifetime, which is enhanced by as much as 240% compared with conventional treatment. It is concluded that through correct preflush design and formation conditioning, scale-inhibitor-squeeze lifetime can be extended significantly.