The Influence of Carbonate Dissolution on Physical Properties and Pore Structure of Sandstone Reservoir

The change of physical properties, mineral composition and pore structure of Chang 6 sandstone cores with different permeability levels in Ordos Basin before and after carbonic acid dissolution were systematically studied. The results show that for rock samples with low permeability, the content of other mineral components except quartz decreases due to the dissolution of carbonate water, while for rock samples with high permeability, due to the small specific surface area of pore space, the interaction strength between minerals and carbonate water is weak, and a small amount of calcite and feldspar are dissolved and the content decreases, while the relative content of other minerals increases. With the continuous injection of carbonate water, the porosity and permeability of the core with a permeability of 0.1 mD increase continuously, and the porosity and permeability of the core with a permeability of 1.0 mD decrease first and then increase. When the core permeability is 10 mD, the core porosity and permeability decrease continuously. In general, the relative change rate of porosity is between -5.77% and -3.68%. The relative change rate of permeability was between -21.87% and -18.47%. The research results reveal the characteristics of pore throat structure changes under the interaction between sandstone with different porosity and permeability levels and carbonate water, which can provide an important theoretical basis for the formulation of CO₂ displacement and storage schemes in low permeability reservoirs.