EXPERIMENTAL INVESTIGATION ON THE INTERACTION OF ROCK-WATER-SUPERCRITICAL CO2 FLUID IN A POTENTIAL SITE FOR GEOLOGICAL STORAGE OF CO2 IN TAIWAN

The objectives of this study are to experimentally investigate the extent that the trace elements in sandstone and shale either dissolve into formation water or absorb from formation water during the interaction of rock-water-supercritical CO₂ fluid if the CO₂ is injected into the sandstone (depth=2279-2642 m) in a gas well in Central Taiwan that contains formation water (depth= 2292-2333.5 m). The sandstone is intercalated with 2 m thick shale at depth of 2372-2374 m. These formation water, rock fragments of sandstone and shale were collected for the simulation experiments of the rock-water-supercritical CO₂ fluid interaction lasting for 35 days in the laboratory, which was conducted in a high pressure clave simulation facility under the conditions of high pressure (250 bars) and high temperature (100°C) in which the injected CO2 became supercritical fluid. The experimental results showed that V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, and Sb in sandstone and shale tended to more easily dissolve into formation water in the presence of CO₂ fluid than in the absence of CO₂ fluid. However, Ba did not tend to easily dissolve into formation water, but more easily absorb onto sandstone and shale from formation water. The shallow groundwater in the upper aquifer may be contaminated with those trace elements released from the underlying sandstone and shale in the presence of CO₂ fluid under such high pressure (250 bars) and temperature (100°C).