Effect of CO Phase States and Flow Rate on Salt Precipitation in Shale Caprocks-A Microfluidic Study.

Fracture networks inside the caprock for CO storage reservoirs may serve as leakage pathways. Fluid flow through fractured caprocks and bypass conduits, however, can be restrained or diminished by mineral precipitations. This study investigates precipitation of salt crystals in an artificial fracture network as a function of pressure-temperature conditions and CO phase states. The impact of CO flow rate on salt precipitation was also studied. The primary research objective was to examine whether salt precipitation can block potential CO leakage pathways. In this study, we developed a novel microfluidic high-pressure high-temperature vessel to house geomaterial micromodels. A fracture network was laser-scribed on the organic-rich shales of the Draupne Formation, the primary caprock for the Smeaheia CO storage in Norway. Experimental observations demonstrated that CO phase states influence the magnitude, distribution, and precipitation patterns of salt accumulations. The CO phase states also affect the relationship between injection rate and extent of precipitated salts due to differences in solubility of water in CO and density of different CO phases. Injection of gaseous CO resulted in higher salt precipitation compared to liquid and supercritical CO. It is shown that micrometer-sized halite crystals have the potential to partially or entirely clog fracture apertures.