To clarify the driving mechanisms of carbon capture, utilization, and storage (CCUS), phase behaviors in bulk CO2-oil-brine system is inevitably foundational investigation. In this study, we conducted pressure-volume-temperature tests under single-variable control in laboratory with in-situ crude oil and synthetic brine samples. First, constant composition expansion tests were designed to examine saturation pressure between CO2 and oil phases with varied CO2 mole concentration and temperature, respectively. Meanwhile, as a major mechanism for carbon storage, CO2 solubility in brine and oil was then measured with changing pressures at a specific reservoir temperature. Growth of the saturation pressure was constantly detected with increasing CO2 mole concentration and temperature, respectively. With sufficient CO2 guaranteed during the tests, we found that CO2 solubility in tested liquids was strengthened by the pressure increase as expected. Moreover, within the same pressure range, incremental CO2 solubility in oil was about ten times larger than that in the brine, which indicated potentially underestimated CO2 storage capacity in depleted oil reservoirs.
Keywords CCUS, PVT, CO2 solubility, Phase behavior, Constant composition expansion