CO2 Injection Strategies Accounting for Caprock Integrity: A Case Study of the Changyuan Anticline

CO2 injection alters the evolution of the subsurface pressure regime, and overpressure within the caprock compromises caprock integrity, thereby diminishing storage performance and potentially posing environmental risks. Based on the dimensions of the GTZ secondary anticline within the Changyuan Anticline, a three-dimensional saline-aquifer storage model with an explicit anticline geometry was constructed. The analysis evaluated the effects of engineering parameters and anticline size on the spatiotemporal evolution of caprock overpressure and on the timing of hydraulic sealing failure, and examined the effectiveness of coupled operational schemes for controlling caprock overpressure. Results show that sustained CO2 injection increases pore pressure; buoyancy drives upward migration, focusing pressure at the caprock base and producing overpressure. A strategy combining a horizontal well, an extended injection interval, reservoir stimulation, and intermittent injection effectively reduces caprock overpressure. For anticline settings, selecting saline aquifers with a shorter major-axis length and a larger closure height further lowers overpressure and increases safety margins. Under an optimized scheme, the annual injection rate can be increased from 0.60 Mt/a to 0.75 Mt/a. Injection design should be tailored to the demonstrated caprock integrity in geological storage projects.