Mohammad Badghaish, Mohammed Alarfaj, Hamad Alsunaid, Brandon Schwartz*, Penn State University
The cost of capturing CO₂ from dilute waste streams has proven financially prohibitive to the widespread deployment of geologic carbon sequestration and represents a parasitic load on current point source emitters. Capture through amine towers is designed to conserve pore volume for greenhouse gases and to mitigate pressure-driven risks. However, the most recent data show ample pore volumes exist to manage carbon emissions during the 21st century energy transition, including between 2 and 22 trillion tons of storage in US saline aquifers alone. Practical strategies such as lower injection rates through multiple wells can be used to reduce pressure buildup. We explore the technical differences between pure CO₂ injection in a saline aquifer and flue gas injection, comparing on the basis of equal volumes of CO₂ sequestered. Subsurface considerations include the flue gas’s fluid compressibility as a function of composition, injectate solubility at the brine interface, and rock-fluid interactions that lead to higher pressure buildup. Pressure-driven risks increase as the concentration of CO₂ decreases relative to N2, and a geomechanical model is proposed that shows the impact of changing flue gas concentration on pressure buildup. The cost of carbon capture is compared to the cost of compressing and transporting an equal volume of CO₂ as a function of CO₂ composition in the waste stream. We explore managing pressure-driven risk due to increased volumes during flue gas injection as a function of increased well spacing and increased number of injection wells to distribute the injectate volume appropriately. We find that for projects where the cost of compression is low compared to the cost of capture, flue gas injection represents an opportunity for increased implementation of carbon sequestration.