Controlled delivery and release of asphaltene inhibitors

Asphaltene is a poly-disperse distribution of the heaviest and most polarizable fraction of crude oil. The asphaltene aggregation and subsequent precipitation in nonpolar media may have a profound effect on plugging wellbores and production equipment. This thesis develops an innovative concept of using nanoemulsions (NEs) as carriers for delivering asphaltene inhibitors (AI) and control their release inside porous media to prevent asphaltene agglomeration and deposition. The new concept could provide tremendous value by i) improving the stability of asphaltene, ii) reducing the usage of AI, iii) extending the treatment time via slow release, and iv) allowing good adsorption of AIs on the formation surface to increase asphaltene treatment efficacy. Four areas were studied including i) the preparation of NEs and NEs loaded with AIs; ii) asphaltene aggregation/precipitation prevention and AI release kinetics study, iii) molecular structure alteration of asphaltene in the presence of NEs, and iv) controlled the delivery of these NEs through porous media.
Firstly, we developed a novel strategy to manipulate the occurrence of Ostwald ripening to form stable NEs by using oil-soluble inhibitors such as dodecylbenzene sulfonic acid (DBSA) and the polycyclic aromatic hydrocarbon phenanthrene (phe) to the oil phase. Two methods, one static based on Brownian motion and one dynamic based on centrifugal force, were used to evaluate and confirm the physical stability of NEs. It was found that with the help of inhibitors, the NEs were very stable even after centrifuging under 500 g for 1 hour or 4 weeks’ storage under ambient conditions.
Following this, a novel approach by using NEs for controlled delivery and release of AI was proposed to minimize asphaltene precipitation with reduced AI amount. The amount of inhibitor could be significantly reduced by ~ 20 times by using the DBSA NEs, with largely extended release time. Continuing our work on the controlled release of AIs by using NEs, a mechanistic understanding of the controlled release effect was proposed based on the effect of DBSA NEs on the asphaltene particle morphology variation, which was related to the hydrophilicity of DBSA and the strong intermolecular interactions among all DBSA NE’s components. The AI release mechanism was compared with eight kinetic models, and the Korsmeyer-Peppas release model was identified. The evidence of multiple intermolecular interactions and quantitative FTIR study showed that the controlled release effect and long term asphaltene stability were due to the decrease of the aromaticity and the reduction in the aliphatic side chains of asphaltene. The refractory nature of asphaltenes was investigated by thermogravimetric analysis (TGA), which revealed that the structure of asphaltene was improved considerably and the coke yield was decreased by 62% due to the decrease of the cluster size and the increase of the stacking distance between aromatic sheets.
Finally, DBSA NEs were used as carriers for delivery and controlled release of DBSA for enhanced displacement of asphaltene on the sandstone rock surface. It showed that comparing to DBSA injection alone, the cumulative asphaltene recovery efficiency was increased by 16.4%. A combination of three possible mechanisms, including slow release kinetic, electrokinetics repulsive expansion, and interfacial and wettability properties were discussed to illustrate the mechanism of the enhanced asphaltene displacement.