Evaluation of in-situ reservoir blocking by sodium carbonate gel formed from sodium metasilicate solution and injected CO2 for CO2 sequestration

Preventing channeling flows during enhanced oil recovery targeting heterogeneous or fracture type reservoirs and leakage flows from saline aquifers containing CO2 remains a challenge. This study evaluated the potential of in-situ gelation as a blocking agent in a heterogeneous reservoir using the reaction between aqueous solution of sodium metasilicate (Na2SiO3 · 9H2O; S–MS) and dissolved carbon dioxide (CO2). Both Raman and scanning electron microscopy/energy dispersive X-ray (SEM-EDS) spectroscopy revealed that the gel was a sodium carbonate type (S–C-gel). Physical characterization of the S–C-gel including the gelation time, gel strength and stability, were investigated in respect of S–MS concentration, temperature, salinity (NaCl), divalent ion concentration (calcium, Ca2+) as well as CO2 injection pressure. Gelation time after CO2 gas injection was around 1 to 24 h depending on temperature and pressure. Gel strength increased with higher S–MS concentration (≤ 10 wt%) and CO2 gas pressure (≤ 5.5 MPa). Threshold pressure gradient (TPG) and gas permeability of the sandstone core filled with in-situ gel increased by 2.6 times and decreased about 1/10, respectively, compared with the water saturated core. These promising findings herein could be extended to CO2 sequestration.