Abstract Brittleness and in-situ stress states are known critical indicators for screening prospected layers during hydraulic fracturing in unconventional reservoirs. Brittleness can be inferred from mechanical parameters and mineralogical data, primarily using empirical relations, although an incomplete dataset limits their use. Therefore, a dataset with a systematic framework was designed based on well logs, and details core data spudded in the Permian Roseneath and Murteree shales from the Cooper Basin, Australia. Petrophysical and geomechanical models were designed to indicate shale mineralogy, total organic richness, porosity, in-situ stress conditions, brittleness index, pore pressure, and fracture pressure gradient. After a review of various definitions of brittleness index (BI) in recent literature, it will be argued that the definition of a brittleness index is with reference to either elastic parameters, mineralogical composition, or strength parameters. Consequently, a higher brittleness index is assigned to quartz and siderite rich rocks than to clay, organic matter, and porosity rich rocks. Some recent definitions of BI are therefore useful for indicating rock types, but brittle/ductile behavior is not necessarily any indicator of brittle/ductile failure during stimulation. It is therefore proposed that an accurate BI must be incorporated into a geomechanical model. This new model will comprise the following properties: elastic and strength parameters, in-situ stress state, fracture pressure gradient, and pore pressure. Such an integrated model can be used to find 1) Fracture barriers (the layers hindering fracture growth); 2) Potential layers that enhance fracture growth, and; 3) Direction of induced fractures on the bases of the stress regime.

中文翻译：

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利用岩石物理和地质力学综合方法优化水力压裂对页岩气藏进行有效评价：澳大利亚库珀盆地二叠纪 Roseneath 和 Murteree 页岩气藏的案例研究

摘要 脆性和地应力状态是已知的非常规油藏水力压裂过程中筛选有前景层的关键指标。脆性可以从力学参数和矿物学数据中推断出来，主要使用经验关系，尽管不完整的数据集限制了它们的使用。因此，基于测井数据设计了一个具有系统框架的数据集，并详细介绍了在澳大利亚库珀盆地二叠纪 Roseneath 和 Murteree 页岩中挖掘的核心数据。岩石物理和地质力学模型旨在指示页岩矿物学、总有机质丰富度、孔隙度、地应力条件、脆性指数、孔隙压力和裂缝压力梯度。在回顾了近期文献中脆性指数 (BI) 的各种定义后，有人会争辩说，脆性指数的定义是参考弹性参数、矿物成分或强度参数。因此，与富含粘土、有机质和孔隙度的岩石相比，富含石英和菱铁矿的岩石具有更高的脆性指数。因此，BI 的一些最新定义可用于指示岩石类型，但脆性/韧性行为不一定是增产过程中脆性/韧性破坏的任何指标。因此建议必须将准确的 BI 纳入地质力学模型。这个新模型将包括以下属性：弹性和强度参数、地应力状态、破裂压力梯度和孔隙压力。这种集成模型可用于发现 1) 裂缝障碍（阻碍裂缝生长的层）；2) 促进裂缝生长的潜在层，以及；3) 基于应力状态的诱导裂缝方向。