MICRO-CT CHARACTERIZATION OF THE REACTION BETWEEN WELLBORE CEMENT AND SULFURIC ACID IN CO2 GEOLOGICAL STORAGE ENVIRONMENT

In order to explore the process of acid-induced corrosion of wellbore cement and the formation and development of leakage channel in wellbore cement under the condition of CO2 geological storage, wellbore cement samples were immersed in sulfuric acid solution for 3.5, 7 and 14 days, and the samples after reacting with sulfuric acid were scanned by a micro-CT scanner. Sulfuric acid solution was used to simulate the low pH and high sulfate ion content in deep formation waters after injection of CO2. The reaction results with different pH values and different cement curing conditions were compared. The results show that there was significant dissolution in the exterior of the cement sample, and the dissolution surrounding a penetrating hole at the center of the sample was limited. Cracks in cement samples were found after reacting with sulfuric acid, which has a negative effect on the integrity of the cement sample. Sulfate ions led to small amount of calcium sulfate precipitation, but had little effect on the overall pore structure and morphology of the sample. Comparison between results in this study and results of CO2-rich brine exposure in a previous study provides valuable information on how low pH-induced corrosion and bicarbonate-induced cement carbonation contribute to pore structure and mineral composition evolution of wellbore cement in CO2 geological storage environment.