Mechanical Properties and Failure Behavior of Shale under the Influence of CO₂

To clarify the evolution law of shale mechanical properties under the action of CO₂, CO₂-water-rock reaction experiments and uniaxial compression experiments were carried out on the shale of Fengcheng Formation in the Junggar Basin, and stress-strain curves, mechanical strengths, and failure characteristics were obtained. The results demonstrated that the stress-strain curve has four stages: compaction, elastic deformation, plastic yielding, and post-peak damage. As CO₂ soaking time increased, the compaction stage was prolonged, accompanied by a change in the post-peak characteristic from a "steep" drop to a "step-like" fall. The compressive strength and elastic modulus decreased by CO₂ dissolution and adsorption. The shift in failure mode from brittle to plastic resulted in increased fracture complexity. The reduction in shale compressive strength helped reduce fracture initiation pressure, form complex fractures, and increase fracturing efficiency. However, it also increased the risk of CO₂ leakage and affected the long-term stability of CO₂ sequestration. Research results can provide theoretical reference for the design of the pre-CO₂ fracturing and the evaluation of the safety of carbon sequestration in shale reservoirs.