Study on Effect of Supercritical Carbon Dioxide on Mechanical Properties of Tight Sandstone Reservoir in Sichuan Basin

In order to study the influence of supercritical carbon dioxide on the mechanical properties of tight sandstone reservoirs in the Sichuan Basin and to understand the interaction mechanism between supercritical carbon dioxide and tight sandstone, methods such as triaxial compression experiments, rock morphology analysis experiments, and whole rock analysis experiments were used to clarify the influence of supercritical carbon dioxide on the mechanical properties of sandstone in the Sichuan Basin and to preliminarily analyze the interaction mechanism between supercritical carbon dioxide and sandstone. The research results show that: (1) under the action of supercritical carbon dioxide,the compressive strength of sandstone will decrease significantly, the Young's modulus will decrease, the Poisson's ratio will increase, and the brittleness will increase; (2) with the increase of the time of supercritical carbon dioxide, the compressive strength decreases faster, the Young's modulus gradually decreases, the Poisson's ratio does not change much, and the brittleness increases. The failure mode of sandstone changes from shear failure to the complex failure mode of “tensile failure + shear failure”; (3) Supercritical carbon dioxide will not only change the pore structure of sandstone, but also the mineral composition of sandstone. The conclusion is that supercritical carbon dioxide will react chemically with some minerals in sandstone, causing mineral dissolution and precipitation, and to some extent changing the pore structure of sandstone, resulting in the degradation of its mechanical properties. The research results of this paper have certain guiding significance for the design of supercritical carbon dioxide fracturing in the Sichuan Basin.