Petrophysical changes of carbonate rock related to CO₂ injection and sequestration

Efficient carbon dioxide injection and potential effects on injection costs require an understanding of the rock-fluid geochemical interactions during a CO₂ storage operation. Dissolution and/or precipitation of minerals during carbon dioxide injection is believed to be the main reason for changes in the formation properties affecting flow and injectivity, particularly within carbonate rock. In this study, we designed four distinct experiments to investigate changes in porous media due to carbon dioxide injection. We used cores with a range of features to conduct core flooding experiments that explored the effect of rock mineralogy and distance from the injection point, as this knowledge is crucial to estimate the success of future storage operations. Qualitative and quantitative measurements such as the XRD, CT scanning, porosity, and permeability, were performed before, during, and after the core floods as a means of studying the effect of carbon dioxide flooding using 55 to 100 pore volumes of throughput. The core floods resulted in a significant increase in permeability (400-fold) and porosity of the sample composed of minerals that were soluble in an acidic environment and a 50% decrease in permeability in the sample composed of acid-insoluble minerals. The most significant changes are the result of forming wormholes through the samples, confirmed by CT scanning, but the details of their formation are more complex than this general statement and are discussed in this paper.