|dc.description.abstract||Oilfield scale is a significant problem in oil production which arises due to temperature and pressure changes and mixing of incompatible brines when a well is produced. The most successful and commonly used strategy for mitigating against oilfield scale is the application of scale inhibitor squeeze treatments. A squeeze treatment is applied to the production well, and involves several stages, which are: pre-flush, main treatment, overflush, shut-in and back-production. During a treatment, a scale inhibitor adsorbs or precipitates into the formation, and its desorption/dissolution into the produced water when the well is put back into production prevents scale formation. A well must be re-squeezed before the scale inhibitor concentration in the produced water falls below the minimum inhibition concentration (MIC) required to prevent scaling.
This work focuses on the pre-flush stage of a squeeze treatment, in which mutual solvents are applied in order to prepare the well for a treatment. This is the least investigated aspect of squeeze treatments, and the one with the greatest opportunity for potential optimisation. Fundamental to understanding how to best apply mutual solvents (MS) in squeeze treatments, to achieve squeeze lifetime enhancements and to mitigate any formation damage risks, is understanding MS phase behaviour, the transport of MS through the porous medium and MS/mineral surface conditioning effects (e.g. wetting changes).
In this work, the phase behaviour of various mutual solvents is investigated in oil/brine/mutual solvent systems. Effects of salinity and chemistry are determined at field relevant conditions. The influence of scale inhibitors on phase behaviour is also investigated and mutual solvent blend design is examined. The work also develops a quantitative understanding of the phase behaviour of mutual solvents and employs that in the development of semi-empirical and thermodynamic models for describing the phase behaviour. Practical analytical tools are also developed to aid mutual solvent investigations as well as analysis in the presence of mutual solvents. Transport studies of MS in sand packs are used to investigate the transport of mutual solvents in single and multiphase systems. Numerous field solutions can be obtained from this work, but more importantly, this work enables and forms the basis for future mutual solvent investigations in the context of scale inhibitor squeeze treatments||en