Understanding controls on mechanical properties of organic-rich shale is essential in exploration and successful production from hydrocarbon reservoirs. In previous works, most researchers have focused on the influence of thermal maturity and organic type on elastic and viscoelastic properties of organic matter. However, fracture toughness, an important parameter in engineering design, has been less investigated. In this study, shale samples with different thermal maturity were obtained by programmed heating. Then, the fracture toughness of organic matter in shale samples was measured using an energy-based nanoindentation method, and the influence of geochemical features was determined. Organic matter was classified as inertinite, vitrinite and bitumen, and the fracture toughness of tested organic matter was in the range of 0.023–0.081 MPa*m. The results indicated that the fracture toughness of vitrinite increased with thermal maturity. Additionally, both the reduced modulus of vitrinite and bitumen increased, while the viscosity of all types of organic matter decreased, with higher levels of thermal maturity. Moreover, a comparison between mechanical parameters of artificially-matured samples, and those of natural samples, was conducted. The fracture toughness of organic matter obtained in this study is crucial for parameter estimation of fracture propagation and homogenization models.

中文翻译：

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人工熟化页岩样品干酪根断裂韧性的控制：基于能量的纳米压痕分析

了解富含有机质页岩机械特性的控制对于油气藏的勘探和成功生产至关重要。在以往的工作中，大多数研究人员关注热成熟度和有机类型对有机质弹性和粘弹性特性的影响。然而，断裂韧性作为工程设计中的一个重要参数，目前的研究较少。本研究通过程序加热获得了不同热成熟度的页岩样品。然后，采用基于能量的纳米压痕法测量页岩样品中有机质的断裂韧性，并确定地球化学特征的影响。有机质分为惰质体、镜质体和沥青，测​​试有机质的断裂韧性范围为0.023~0.081 MPa*m。结果表明，镜质体的断裂韧性随着热成熟度的增加而增加。此外，镜质体和沥青的降低模量均增加，而所有类型有机物的粘度均下降，热成熟度水平较高。此外，还对人工熟化样品和天然样品的机械参数进行了比较。本研究获得的有机质断裂韧性对于裂缝扩展和均质化模型的参数估计至关重要。