Carbon migration and phase distribution patterns in CO2 geological utilization and storage

CO2 geological utilization and storage (CGUS) is an important method to reduce carbon emissions in the context of “carbon peaking and carbon neutrality” goals. The previous studies mostly focused on geological utilization, but paid little attention to the quantitative evaluation of the carbon storage potential of strata, especially the potential of CO2 mineralization. By means of program development, this paper introduces the flash calculation into the open source software to simulate the reaction solute transport, and then establishes a 3D geological model of H59 block of Daqingzijing Oilfield in the Songliao Basin by using the improved software. In addition, the formation parameters of the model are corrected through history match of injection and production process. Finally, the spatio-temporal evolution of CO2 migration and phase transformation in different injection stages and after the end of injection and production is quantified with the corrected model. And the following research results are obtained. First, under the condition of miscible CO2 flooding in the reservoir, CO2 presents as gas phase in a small range at the end of injection well. And after contacting the front of oil phase, CO2 gets weakened by buoyancy, gradually tends to be evenly distributed in the vertical direction, and advances uniformly to the end of the production well. Second, more than 70% of the injected CO2 is dissolved in the oil phase in both the gas-water injection stage and the gas injection stage, but the content of CO2 dissolved in the water phase increases significantly in the gas-water injection stage. Third, the phase evolution after the end of injection and production is characterized by the gradual transformation of CO2 dissolved in water phase into mineral phase, but the transformation trend of CO2 dissolved in oil phase into the free gas phase. Fourth, after the end of injection and production, the main mineralization process is the dissolution of chlorite and iron dolomite to produce iron and calcium ions, which combine with carbonate ions to form precipitated minerals (carbon fixing minerals) such as calcite and siderite, and the dissolved minerals are mainly potassium feldspar, calcium montmorillonite, iron dolomite and chlorite. In conclusion, based on the field measurement data, the CO2 migration and phase distribution patterns are theoretically studied by using the CGUS component simulation software embedded with flash calculation, and the research results are of important significance to guide efficient CO2 EOR and storage. © 2024 Natural Gas Industry Journal Agency. All rights reserved.