Abstract:

In order to study the physicochemical reaction law of carbonate rock reservoirs under the condition of CO₂ geological storage, lab experiments on the reaction of carbonate rocks and supercritical CO₂ under reservoir conditions were carried out with the carbonate reservoir of the Sinian Dengying Formation reservoirs in the Sichuan Basin as the research object. The response characteristics of carbonate porosity, permeability, and pore structure to supercritical CO₂ environment were investigated by the pressure pulse attenuation method, scanning electron microscopy method, and nuclear magnetic resonance method. The test resulted in an increase both in the porosity and permeability of the carbonate rock. The maximum porosity change rate is 32.35 % and the permeability increases by eleven times. Additionally, micro-fractures appear after the test, and the proportion of the micro-fractures with the aperture of 20~50 μm increases. By using X-ray diffraction and contact angle techniques, the mineral makeup and wetability of carbonate rocks were examined. The average content of main minerals quartz increased by 12.6 %, the average content of calcite decreased by 22.3 %, and the hydrophilicity increased. Brazilian splitting technique was used to examine the mechanical characteristics of carbonate rocks both before and after supercritical CO₂ immersion. The tensile strength of carbonate rocks was discovered to have fallen by 18.28 %, causing damage to the rocks, and the compaction stage of the load-displacement curve was longer. This work examines the effects of supercritical CO₂ dissolution on the porosity, permeability, mineral composition, and rock mechanical characteristics of carbonate rocks, and provides theoretical evidence for the geological storage of CO₂ in carbonate reservoirs.

Key words: supercritical CO₂, carbonate rock, dissolution, permeability, rock mechanical properties