This thesis presents a systematic experimental and numerical investigation into the thermal dynamics of CO2 injection into porous media, focusing on the Joule-Thomson (JT) cooling effect under conditions relevant to Carbon Capture and Storage (CCS) in depleted reservoirs. The purpose of the study was to deconvolve the mechanisms that govern cooling and to validate numerical models against laboratory data.

Experiments were conducted on two contrasting sandstones: a low-permeability (0.37 mD) Kentucky core, analogous to tight reservoirs, and a high-permeability (1-2 D) Bentheimer core. The cores were instrumented with distributed temperature and pressure sensors to capture transient thermal fronts during CO2 injection. In the low-permeability Kentucky core, the JT cooling was driven by the significant pressure gradient across the porous medium itself. In contrast, the high-permeability Bentheimer core required an artificial inlet pressure drop to initiate cooling; subsequent thermal transport was found to be dominated by the high cooling power of phase change (evaporation) rather than continuous isenthalpic expansion.

Across both types of rock, a systematic phase boundary offset was observed, with phase transitions occurring at pressures 2-4 bar lower (or 2-3 K higher) than predicted by bulk CO2 thermodynamics. Rigorous analysis demonstrates that this significant offset cannot be explained by classical confinement theories such as the Gibbs-Thomson or Kelvin effects, pointing to a more complex interplay of non-equilibrium thermodynamics, capillary phenomena, and rock-fluid interactions.

Numerical simulations using the Delft Advanced Research Terra Simulator (DARTS) successfully reproduced general cooling trends but highlighted critical model requirements. High-resolution Equation of State (EOS) tables (>2000 points) were essential for precision, while the absence of a correct CO2 gas-liquid relative permeability model limited the ability to capture the pressure build-up observed experimentally due to accumulation of the liquid phase.

The findings demonstrate that, while JT cooling is a measurable and critical process, its prediction requires models that incorporate pore-scale physics beyond bulk thermodynamics. The results provide a validated data set and a refined understanding of the coupled thermal-hydraulic processes that govern near-wellbore cooling during CCS operations.