Experimental study of scCO2 injection strategies: Effects on geochemical reactions and reservoir properties in sandstone and carbonate formations

Carbon dioxide (CO₂) storage in geological formations is a promising strategy for mitigating greenhouse gas emissions. However, the injection of supercritical CO₂ (scCO₂) induced a geochemical reaction in the host rock. While the different causes of these reactions have been studied, the effects of different injection strategies are understudied. This study uses core-flooding equipment to investigate the effects of three different scCO₂ injection strategies-continuous scCO₂ injection (CCI), Water or Brine alternating scCO₂ injection (WAG), and Simultaneous brine or water and scCO₂ Aquifer injection (SAI)- on the petrophysical, mineralogy, and microstructural properties of the Gray Berea sandstone and Indiana limestone sample using X-ray diffractometer (XRD), CoreLab UltraPore^TM300 Ultra K 500⁺ and Scanning Electron Microscope-Energy-Dispersive X-ray Spectroscopy (SEM-EDS). Core-flooding experiments were conducted under dynamic flow conditions at 75, 225, and 525 pore volumes (PV) to simulate short-, intermediate-, and long-term CO₂ storage scenarios. Sandstone permeability dropped most under WAG and SAI (∼35 %), with CCI showing a 6.8 % reduction. Carbonate porosity showed an overall gain of 2.5 %–3.3 %, increased permeability under CCI (20.3 %), WAG (4.8 %), and declined under SAI. Elemental analysis showed up to a 50 % increase in Ca and 40.6 % in C in sandstone (CCI), indicating significant carbonate precipitation, while limestone samples exposed to SAI exhibited Al and Si increases of up to 550 % and 322.2 %, respectively, highlighting more intense silicate mineral formation compared to sandstone with microstructural changes observed across all injection methods, especially at extended exposure durations.

These changes are primarily driven by the dissolution of the host rock, acidification, saturation effects, fluid-rock interaction dynamics, etc. The sequence of the dissolution, precipitation, formation of new minerals, and fine migrations also contributes to alterations in pore structures and fluid flow pathways. WAG indicates a balanced approach to the other two injection strategies. However, the reduction in permeability is not desirable.