Experimental evaluation of adiabatic cooling due to CO2 injection into sandstone formations

This paper presents a systematic experimental investigation of Joule–Thomson (JT) and evaporative cooling during CO 2 injection into porous media under conditions relevant to depleted-reservoir Geological Carbon Sequestration (GCS). Core-flooding experiments were performed on two sandstones with contrasting permeabilities. Distributed pressure and temperature sensors recorded the transient thermal response during CO 2 injection, revealing different cooling regimes. In the low-permeability Kentucky core, cooling was dominated by distributed isenthalpic JT expansion within the porous medium, whereas in the high-permeability Bentheimer core, temperature evolution was governed primarily by phase-change (evaporative) cooling triggered by localised inlet pressure losses. This contrast shows that in high-permeability systems, cooling can be controlled by near-wellbore or boundary-imposed restrictions, whereas in tight rock, the porous medium itself dictates the spatial pattern of expansion and cooling. Across both cases, apparent phase transitions consistently occurred at lower pressure, or equivalently higher temperature, than predicted by bulk CO 2 phase boundaries, under transient porous-media conditions. Complementary simulations with the open-source Delft Advanced Research Terra Simulator (open-DARTS), driven by the measured inlet pressure and including conductive heat exchange with the holder, quantitatively reproduce the tight-core sensor record and show that the apparent phase-boundary shift is consistent with local heat exchange at the measurement locations. The results provide laboratory quantification of evaporative cooling during CO 2 expansion in porous media, helping to uncover some of the phenomena at play in near-wellbore thermal behaviour during CCS operations in depleted fields.