Experiment on the influence by supercritical CO2 at the casing cement - sandstone interface

CO2 geological storage is the one of the methods to prevent the global warming. In this method, the most important thing is to prevent leakage of CO2 from the underground reservoir. If CO2 leaks to the surface, it may go up along the casing cement - sandstone interface due to the degradation of the casing cement. Thus we have to understand how CO2 affect the casing cement - sandstone interface. The present work is intended to know what kind of chemical reactions are caused at the casing cement - sandstone interface when exposed to supercritical CO2. Experimental specimens used in the present work are composed of Berea sandstone, Tako sandstone and oil well cement. The sandstones are prepared in the form of cylinder with the diameter of 25 mm and the length of 90 mm, and drilled holes with the diameter of 7 mm at the center. Then oil well cement is put in the holes. These experimental specimens and the distilled water are set in the cambers. Then the chambers are backfilled with CO2. The temperature and the pressure in the cambers are set at 60℃ and 10MPa. In these conditions, CO2 becomes supercritical fluid. These experimental conditions are to be maintained for 3 weeks. After the experiments, the specimens are examined by stereoscopic microscope, polarizing microscope and scanning electron microscope (SEM), and measured by means of X-ray analysis. The water left in the chambers is measured by means of atomic absorption analysis.