Experimental studies of injectivity reduction due to carbonate mineralization

The geological sequestration of carbon dioxide (CO 2 ) has been proposed to be one of the most effective and advanced technologies for reducing CO 2 emissions. Geochemical trapping is regarded as an alternative process for CO 2 sequestration. Carbonate mineralization takes advantage of permeability reduction to seal formations, decreasing the risk of CO 2 leakage and increasing storage safety. Because precipitation rates tend to be faster and the solubility product shows a lower value at higher temperatures, the interaction of calcite and kaolinite‐rich rock with CO 2 ‐water is expected to form a scale in geothermal reservoirs. The Ca-super-2+ released from rocks can be removed as carbonate minerals during CO 2 injection into aquifer rocks. However, the effects of the amount, timing, and location of carbonate precipitation on the permeability of reservoirs are not clear. In order to predict the time and space of clogging by carbonate precipitation, column flow experiments were performed under various conditions. Supersaturated carbonate fluids were obtained from the Ogachi, Matsushiro, and Namikata field sites. These were introduced in flow experiments over a wide range of temperatures (20∼185 °C), pH (6∼11), and concentrations of reactants ([Ca] = 18∼850 mg/l) to vary the growth rate of carbonate minerals. The reduction of injectivity shows that fluid flow velocity controls the distribution and amount of carbonate deposition. The product of CO 2 concentration and S.I., defined as the logarithm of the ion activity product per the solubility product, might be the index for predicting the time required for clogging to be observed. © 2013 Society of Chemical Industry and John Wiley & Sons, Ltd