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. The potential of in-situ gelation as a blocking agent in a heterogeneous reservoir using the reaction between aqueous solution of sodium metasilicate (S-MS) and dissolved CO₂ was studied. 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, was performed 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 hr 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.