Study Of Water-Rock Simulation Experiment And Thermodynamic Influence Mechanism On The Stability Of Typical CO₂ "Carbon-Fixation Mineral"

As the main carbon-fixing mineral for CO₂ geological storage,dawsonite’s stability in the reservoir is controlled by a very complex fluid-rock interaction.Therefore,clarifying the stability influence mode of dawsonite is important for implementation of CO₂ geological storage and solving global problems.In this study,the natural dawsonite-bearing sandstone in Dongying sag was used as the research object,and the CO₂-H₂O-dawsonite-bearing sandstone interaction experiment and TOUGHREACT numerical simulation were carried out under different p H values,temperatures and CO₂ pressures.And through thermodynamic analysis,the CO₂ fugacity value actually acting on the sandstone in the reactor experiment was corrected.Comprehensive use of thin slice identification,scanning electron microscope observation and energy spectrum analysis,X-ray diffraction analysis,water chemical analysis,and dawsonite stability indicator parameters,etc.,the dissolution response of dawsonite and the evolution trend of element composition were systematically studied,the stability influence model of dawsonite was summarized,and the favorable reservoir conditions for CO₂ geological storage were predicted.Dawsonite can maintain high stability under alkaline fluid environment,low temperature and high CO₂ pressure.The transformation of dawsonite by acidic fluids is mainly a"decomposition path"that dissolves the crystal structure by dissolving elements,the Na and Al in the crystal structure will dissolve successively,leading to the continuous decomposition of the crystal structure.The stability of dawsonite gradually decreases with the increase of temperature.The transformation effect of high temperature on dawsonite is mainly to form the"transformation pathway"of boehmite by dissolving the elements and transforming the structure,the content of Na and C decreases with the increase of temperature,and their elemental composition also evolves to O:Al is close to 2:1,and finally transformed into boehmite.The CO₂ fugacity actually acting on dawsonite in the reactor experiment is controlled by the experimental pressure.The increase of CO₂ pressure can improve the thermal stability of dawsonite and inhibit its decomposition;high CO₂ pressure can change the transformation pathway of dawsonite under the action of temperature modification,and its finally elemental composition is mainly C,O,Al and Si.Temperature and CO₂ pressure have a comprehensive effect on the stability of dawsonite.The increase in temperature will reduce the inhibitory effect of CO₂ pressure on the dissolution of dawsonite,making the CO₂ pressure required to maintain the stability of dawsonite corresponding increase.At 120℃,dawsonite reaches a stable state at p CO₂=7.3 MPa.In the process of CO₂ geological storage,select a stable sandstone reservoir with alkaline formation fluid,low formation temperature and relatively high formation pressure as the target layer of CO₂ injection,can provide ideal conditions for CO₂ geological storage and promote the formation and protection of CO₂ trapping minerals,and avoid the occurrence of gaseous escape or the leakage of dissolved"carbon"due to the decrease in the stability of carbon-fixed minerals,ensuring the long-term effectiveness of CO₂ geological storage.