Pre-flush design for extended scale inhibitor squeeze lifetime in limestone reservoir - Laboratory investigations and cost benefit analysis

Scale inhibitor (SI) squeeze treatment is an established practice in offshore fields to prevent inorganic scale deposition in the wellbore and near wellbore formation. 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 rock surface condition. This work 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. Eco-friendly APG surfactants are evaluated with and without alkali and co-surfactants to design the pre-flush composition. A series of coreflood experiments 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 in light of IFT and phase behavior and changes of rock wettability due to pre-flush treatment. The results show that SI squeeze lifetime can be enhanced by as much as 240% when compared to conventional treatment and it 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 competition with scale inhibitor molecules. Cost benefit analysis evince that introduction of the newly designed pre-flush treatment would results in improved economics through reduced treatment frequency, leading to minimized well intervention and consequent production loss. Not enough attention is given on the design/optimization of pre-flush and conditioning of the formation to be used as adsorbent/storehouse of the inhibiting chemical in preferentially oil wet carbonate formations. The applicability of surfactant-alkaline has been long established as means of EOR mechanism but they are rarely investigated for near wellbore treatments to maximize chemical storage and placement; which is what this work has studied.