Super-Critical CO₂ Weakening Effect on Strength of Tight Sandstone With a Weak Plane: Experimental Results and Causes

As a representative technology of non-aqueous fracturing, super-critical carbon dioxide(SC-CO₂) fracturing has become a research focus in the development of tight reservoir. The weak plane is widely distributed in the tight reservoir, such as natural fractures and bedding planes, however the effects of SC-CO₂ on reservoir rocks with weak planes are scarcely found in publications. Two groups of samples with the same angle of the weak plane were used in experimental work. The first group was treated in a closed container filled with SC-CO₂ for 30 days, and Brazilian and triaxial compression tests with SC-CO₂ were performed, and the other group was taken as control experiment without any treatment. In both groups, Acoustic Emission (AE) was used to record the fracture process. The tensile and triaxial compressive strengths of SC-CO₂ were about 60% and 80% of those of untreated samples. It was found that SC-CO₂ advanced the initial stage of the damage, and the damage extension stage lasted for an elongated time. The authors revealed the mechanism of SC-CO₂ affecting the weak plane from the perspective of meso-damage mechanics. This research will be beneficial to understanding the fracturing behavior of the tight sandstone with weak planes during SC-CO₂ fracturing.