The efficiency of Carbon Capture and Storage projects is directly related to the long term sealing ability of cemented sections in wellbores penetrating CO2 storage reservoirs. The microfractures inside the wellbore cement and/or microannulus are possible pathways for CO2 leakage to the surface and/or fresh water aquifers and jeopardize safe and long-term containment of CO2 in the subsurface.
This paper presents an experimental study which investigates the changes inside the cement internal structure when exposed to acidic brine through an artificial fracture. A 30-day long flow through experiment was conducted using a 1 in by 12 in. cement core and CO2 saturated brine, as a permeant, at a flow rate of 2 ml/min in a core flooding apparatus with10 psi and 600 psi of injection and net overburden pressures (Low Pressure-LP experiment). The same experiment was repeated with 1800 psi and 600 psi of injection and net overburden pressures for 10 days in order to account for the effects of pressure on the degradation process of cement (High Pressure-HP experiment). High-resolution X-ray computed tomography was used to image several subvolumes extracted from the flow-through cores. The images were processed and thresholded, followed by calculation of porosity. Total porosity was observed to decrease from 26% to 22% after 30 days of exposure of LP experiment. The HP experiment did not cause any significant change in total porosity possibly due to the short duration of the experiment.