Pre-flush design for extended scale inhibitor lifecycle in limestone reservoir.

摘要

Scale inhibitor (SI) squeeze treatment is an established practice to prevent deposition of inorganic scales in the wellbore and near wellbore formation, particularly in offshore locations. SI squeeze lifetime is measured by the duration for which the concentration of the chemical is released at a concentration above the required minimum inhibitor concentration (MIC). Hence, maximizing SI adsorption to the pore surfaces may proportionately enhance squeeze lifetime. However, most oil-field squeeze scale inhibitors being aqueous-based, it is unlikely to get optimum adsorption on an oil-wet formation due to unfavorable surface condition of the rocks.;This research is targeted towards optimum formation conditioning through an intelligently designed pre-flush treatment so that the adsorption and lifetime of SI in an oil-wet carbonate reservoir are significantly improved. The objective is to develop a surfactant based system to alter near wellbore formation wettability and minimize O-W interfacial tension; to flush out most oil and create the most ideal condition for maximum scale inhibitor adsorption and study the impact on SI squeeze lifetime. Different surfactants of similar base structure are used in the presence as well as the absence of alkali to design the pre-flush composition. The performances of the pre-flush systems are further enhanced by addition of co-surfactant. A series of coreflood experiments with selected pre-flush compositions and SI are conducted in simulated reservoir conditions, using data and materials from a high temperature carbonate oil reservoir from the Middle-East. The results are evaluated with the support of IFT studies, phase behavior analysis and wettability measurements.;The results reveal that scale inhibitor squeeze lifetime can be enhanced by as much as 240% when compared to conventional treatment and has a direct correlation with wettability index and IFT. Anionic surfactant may look more attractive than nonionic surfactant due to favorable wettability alteration and highly reduced IFT, however they may not be the right choice for carbonate formation due to higher adsorption and subsequent competition with scale inhibitor molecules. From this study, it is concluded that through right pre-flush design and formation conditioning, scale inhibitor squeeze lifetime can be extended several folds; ultimately leading to reduced OPEX and minimized well intervention and production loss.