The effect of water alternating solvent based nanofluid flooding on heavy oil recovery in oil-wet porous media

摘要

Solvent flooding is considered as one of the effective methods to recover heavy oil from non water-wet reservoirs where thermal processes are inefficient. We have recently proposed and tested a solvent recovery technique called solvent based nanofluid flooding followed by waterflooding to improve sweep efficiency and recover a medium viscosity heavy oil (100 mPas) in oil-wet porous media. Although solvent based nanofluid improved displacement efficiency as a result of in-situ emulsification, the overall efficiency of the displacement was compromised by solvent gravity override. The objective of this study is to overcome the gravity override effect by conducing water alternating solvent based nanofluid flooding followed by waterflooding. Different injection scenarios with different slug sequences were designed, and the displacement patterns were monitored with a CT-scanner. Moreover, solvent based nanofluid flooding was conducted in a tertiary recovery mode to assess sweep efficiency and oil recovery performances. Imaging showed that solvent based nanofluid was effective in redistributing the preferential flow paths of water slugs and chase water; effluent analysis showed the improvement was due to the in-situ formation of emulsions. However, the overall efficiency of the process suffered from gravity override when conducing the process in a tertiary mode or starting the alternating slug process with the solvent phase. Starting the alternating slug process with the brine phase reduced override and enabled a substantial increase in recovery.