Experimental investigation on CO2-water-rock interactions during CO2 flooding

Injecting CO2 into oil bearing reservoir to displace oil is a viable means of reducing greenhouse gas emissions to the atmosphere and enhancing oil recovery. After CO2 injection, CO2-water-rock interactions are taken place underground, and take effect on the properties of reservoir system, including the mineralogy, the ion composition of formation water, surface topography and the permeability. Those were determined by Xray diffraction (XRD), inductive coupled plasma-atomic emission spectrometry (ICP-AES), scanning electronic microscope (SEM), and sand-pack experiment, respectively. The experimental results show that there is even no change on the surface topography of quartz grains after CO2-water interactions, but there is mineral dissolution/precipitation occurring on the surface of limestone grains after CO2-water interactions. In addition, ion concentrations of Ca2+, Na+, Mg2+ and HCO3-change slightly after CO2-water-quartz interactions due to the chemical stability of quartz, but they will change greatly after CO2-water-limestone interactions due to the release from calcite and dolomite dissolution. Concentrations of ions in water during CO2-water-limestone interactions at different temperatures with reaction time were discussed. Water permeability of the sand-pack filled with mixed quartz and limestone grains increases after CO2 flooding.