Effects of supercritical carbon dioxide fracturing on rock mechanics characteristics of tight sandstone gas reservoirs

Aiming at the development of supercritical carbon dioxide fracture on tight sandstone gas reservoirs, the carbon dioxide fluid effect on rock mechanics is not considered, and the fracturing parameters are not consistent with the oilfield. The test of rock mechanics on tight sandstone by supercritical carbon dioxide fracturing in simulating lab test Confining pressure 38 MPa and temperature 85 ℃, injection pressure of supercritical carbon dioxide is from 0 to 35 MPa. Axial pressure on the tight sandstone result in damage, the stress - strain curve of tight sandstone rock was obtained. With the increase of supercritical carbon dioxide injection pressure, the compressive strength and elastic modulus of tight sandstone decreases, Poisson’s ratio increases, and the brittleness index increases first and then decreases. The fitting brittleness index and carbon dioxide injection pressure are several binomial relations. The maximum of brittleness index is 0.483 5 when injection pressure is equal to 4.55 MPa. The results show that the influence of injection pressure on rock mechanics parameters should be taken into account in supercritical carbon dioxide fracturing. Rock mechanics parameters such as elastic modulus, Poisson’s ratio and brittleness index should influence the initiation and propagation law of cracks in tight sandstone in the late stage.