Experimental study of CO₂ injection in sandstone aquifer for sequestration purposes using X-ray computed tomography

Carbon dioxide storage in saline aquifers has attracted significant attention, due to their potential for long-term secure CO₂ storage. CO₂ injection into deep underground is usually modeled using the classical Buckley-Leverett scheme, generalized to account for partial miscibility and salt precipitation. To verify the applicability of this model, we conducted a series of experiments involving CO₂ injection into saturated aquifer cores, monitored in real-time using an X-ray computed tomography (CT) scanner. These experiments were designed to simulate the conditions of the Stenlille aquifer, allowing us to track the evolution of brine saturation profiles within the cores. Experiments on heptane injection into the same cores were carried out for comparison. The results showed that CO₂ injection exhibited markedly different patterns from both heptane injection and predictions made by the Buckley-Leverett theory. Specifically, CO₂ injection was characterized by early breakthrough, an almost linear distribution of saturation along the core, and a gradual decline in brine saturation with time, even after the injection of several pore volumes, resulting in a high final brine saturation. The experiments are not repeatable, even under identical conditions, although the rock samples remain unaffected. The behavior may be explained by the instable character of displacement, superimposed with the strong capillary effects and slow drying out the brine at the later stages of the experiments.