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 intended to investigate the advantages of combined application 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 tertiary recovery following sea water as secondary recovery mode. This is followed by quaternary recovery using carbonated smart water (CSWI), i.e. smart water saturated with CO2. Three high potential smart water compositions are screened and the best one is chosen for the recovery studies. Produced water samples are analyzed using ICP-MS. The higher recovery efficiency of CSWI are analyzed in support of the NMR porosity distribution, interfacial tension and zeta-potential studies. 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. 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.
From this study it is established that CSWI could be a 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 reduces the requirement for high pressure injection system, the problems of gravity segregation and poor sweep efficiency. A hybrid 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.