Fracability evaluation for unconventional reservoir is critical to the selection of candidate zones for post-frac productivity and plays a key role in fracturing design. Historically, the prevailing models for assessing fracability have been largely relied on brittleness indices. Brittleness indices focus mainly on rock fracture characteristics and offers limited assessment of fracture surface area and the complexity of fracture network, which are more relevant to the practical production. We explored a new fracability evaluation model for unconventional reservoirs from the perspective of fracturing performance, which comprehensively characterizes the rock's ability to generate larger fracture surface areas, more shear fractures and complex fracture networks. The new fracability index considers both the physical processes of rock failure and fracture propagation, and is directly associated with the dynamic production capacities of reservoir. According to the analysis of energy conservation during hydraulic fracturing, we quantify the rock fracture surface area using the KGD and the PKN models. The ability of rock formation to generate shear fractures is mainly influenced by Poisson's ratio and mode II fracture toughness. Brittle mineral content and mineral heterogeneity are two vital criteria that significantly affect the complexity of fracture networks. Based on the logging and production data, this fracability model was applied to two types of unconventional reservoirs. Preliminary results show that this fracability model has an improved correlation with the pay zones and actual production, which is beneficial for optimizing fracturing strategies and identifying production sweet spots.

中文翻译：

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非常规油气藏脆性评价模型——基于水力压裂性能的视角


非常规油藏的脆性评估对于选择压裂后生产力的候选区域至关重要，并在压裂设计中起着关键作用。从历史上看，评估脆性的主要模型主要依赖于脆性指数。脆性指数主要关注岩石破裂特性，对裂隙表面积和裂隙网络复杂性的评估有限，与实际生产更相关。我们从压裂性能的角度探索了一种新的非常规油藏压裂性评价模型，该模型综合表征了岩石产生更大裂隙表面积、更多剪切裂缝和复杂裂隙网络的能力。新的脆性指数同时考虑了岩石破坏和裂缝扩展的物理过程，并与储层的动态生产能力直接相关。根据水力压裂过程中的能量守恒分析，我们使用 KGD 和 PKN 模型量化了岩石破裂表面积。岩层产生剪切裂缝的能力主要受泊松比和 II 型断裂韧性的影响。脆性矿物含量和矿物非均质性是显著影响裂缝网络复杂性的两个重要标准。基于测井和生产数据，该可压裂性模型应用于两种类型的非常规油藏。初步结果表明，该脆性模型与产区和实际产量的相关性更高，有利于优化压裂策略和确定生产甜蜜点。