Experimental Study of the Mode-I Fracture Toughness on Sichuan Basin Gas Shale under Air Dried and Water Saturated Conditions

摘要

Hydraulic fracturing is the primary technology for shale gas development. The fracture toughness of shale is essential to estimate the initiation and propagation of fractures. The Mode-I fracture toughness of the Longmaxi Formation shale, which is taken from the Silurian strata in China Sichuan Basin, is tested in this paper by using the cracked chevron notched Brazilian disc (CCNBD) method. The experimental conditions include air dried shale and water saturated shale. The results show that there is a good quadratic polynomial relationship between the fracture toughness and tensile strength of both the air dried shale and the water saturated shale. The tensile strength can be used to estimate the fracture toughness of shale. The average tensile strength of water saturated shale is 5.3325 MPa, decreased about 35.58% compared to the air dried shale (8.2783 MPa).