干热岩亚临界裂纹扩展的实验研究

Experimental Study on Subcritical Crack Growth in Hot Dry Rocks

通过双扭试验伺服控制压机,在控制位移加载模式下,研究了干热岩在不同浸泡时间下的亚临界裂纹扩展特征。结果表明,干热岩样品亚临界裂纹扩展的门槛值一般约为断裂韧性的80%~90%左右,亚临界裂纹扩展速率与应力强度因子间服从幂律关系;在水化腐蚀环境下,干热岩的断裂韧性与时间呈现较好的负相关性,与干燥状态断裂韧性相比较,浸泡6、8 d时的断裂韧性分别降低了约13.8%和33.7%,同时,干热岩亚临界裂纹扩展参数会发生几个数量级的变化。水化腐蚀可促进干热岩细观人工裂缝形成,细观力学裂纹与主裂缝交汇贯通是其水力压裂形成复杂缝网的力学机制之一。

The subcritical crack propagation characteristics of dry hot rock at different imbibition time are experimentally studied by the double-torque test servo-control device.The results show that the threshold value of subcritical crack propagation in dry hot rock samples is generally 80%~90%of fracture toughness.The subcritical crack growth rate and stress intensity factor obey the power law relationship.Under the action of stress corrosion environment,the fracture toughness of dry hot rock shows a good negative correlation with imbibition time.Compared with the fracture toughness of dry samples,the fracture toughness at 6 and 8 days of imbibition decreased by about 13.8%and 33.7%,respectively,while the subcritical crack propagation parameter A of dry hot rock occurred several orders of magnitude change.It indicates that water environment will promote the formation of meso-artificial cracks in dry hot rocks.The intersection between meso-mechanical cracks and the main cracks are one of the mechanical mechanisms of hydraulic fracturing to form complex fractures.