Effects of Supercritical CO2 Injection on Carbonate Microstructure and Elastic Properties

Nowadays the carbonate rocks are attracting growing interest as a possible site for CO2 geo-sequestration. Monitoring of the injected carbon dioxide is generally an important part of any sequestration project. CO2 is known to change the properties of the hosting rocks and to affect the reservoir characteristics - elastic moduli, reservoir capacity, etc. Thus, predicting changes in microstructures and elastic properties of carbonate rocks after the CO2 injection is of great importance. In the current work we study the effects of sc-CO2 injection on microstructure and elastic properties of carbonate rock. We use microtomographic images of two Savonniere limestone samples, one in its natural state and one after injecting sc-CO2. A statistical analysis exhibits that the injection of sc-CO2 has led to the increase in porosity and changes of the microstructure of the carbonate sample. It has resulted in the increase of the average volume of individual pores and the decrease of the total number of pores. The CO2 injection has increased the mean radii of pore throats, has raised length of pore network segments and makes orientation distribution of meso-pores more isotropic. These changes in microstructure have been reflected in lower numerically simulated elastic moduli of the sample.