Search for an alternative, cheap and environmental friendly EOR method has resulted in the development and subsequent field implementation of Smart Water Injection (SWI) and CO2 injection (COI). Though miscible COI has multi-fold advantages, carbonated water injection (CWI) may surpass COI in terms of volume requirement and efficiency. This research work is focused on finding the benefits of combination of SWI & CWI in terms of reduced residual saturations in oil wet carbonate formation.

In order to measure the recovery efficiency, core flooding experiments are conducted with SWI as a tertiary recovery following sea water secondary recovery. This is followed by quaternary recovery using smart water saturated with CO2 (CSWI). Three high potential smart water compositions are screened and the best one is chosen for oil recovery studies. Effluent samples collected at pre-defined pore volume injection intervals are analyzed in ppm level using ICP-MS. The analysis is supported by NMR porosity distribution studies, interfacial tension and zeta-potential studies.

Core flooding results showed that tertiary recovery with SWI resulted in 4.8 - 9.5% recovery, whereas the quaternary recovery with CSWI resulted in 5.7 % to 13.6% additional oil. The underlying physical processes and the pore-scale mechanisms of fluid-fluid and fluid-solid interactions during SWI-CWI are explained in terms of surface potential, electrical double layer, oil swelling factor, droplet coalescence, wettability alteration and flow diversion due to fluid redistribution within the pore network.

From this study it is established that CSWI could be a novel and promising EOR technique among the latest EOR methods. CSWI has an advantage over COI due to the fact that it exists as a dissolved gas instead of free phase. It eliminates the requirement for high pressure system, the problems of gravity segregation and poor sweep efficiency. Combination of CWI with SWI can make it an effective EOR solution with significant cost advantage, higher oil recovery in addition to the environmental benefits of CO2 sequestration.

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