Abstract Hydraulic fracturing is an important technology widely applied in engineering practice for the exploitation of unconventional oil and gas resources. Further research on its mechanism has the potential to advance the development of unconventional reservoir exploitation. In this study, previously acquired experimental data, including surface fracture image and fluid pressure curve, were used for modelling and comparison. Employing digital core reconstruction and the combined finite-discrete element method, A process of modelling crack geological model was proposed based on the rock surface sketch after fracturing. Two-dimensional models were established according to the surface fracture morphology of specimens. The feasibility of these numerical models was simultaneously verified by fluid pressure curves and the surface fracture morphology obtained in physical experiments. The evolution of fracture morphology during hydraulic fracturing was analysed. Simulation results indicate that: (1) the simulation method of this study is more suitable for simulation of coal hydraulic fracturing than for shale hydraulic fracturing; (2) the rapid rise of fluid pressure might be accompanied with the initiation and development of micro-fractures, leading to the occurrence of larger fractures; (3) the hydraulic fracturing process on the experimental scale could induce significantly larger maximum total area and wider fractures in coal specimens than in shale specimens. This indicates that coal hydraulic fracturing forms more complex fractures than in shale; (4) when the rock elastic modulus increases, the maximum fracture width and fracture total area decreases, and fracture length is extended. (5) The initiation and propagation pressures are positively related to the elastic modulus in the fluid pressure evolution. The crack geological model proposed in this study provides direct guidance for crack reconstruction in simulations. Moreover, the research results may provide a guidance for studies on the evolution of hydraulic fracture under the influence of rock heterogeneity.

中文翻译：

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基于二维地表裂缝形态重建结合有限离散元法的水力压裂数值模拟

摘要 水力压裂是非常规油气资源开发工程实践中广泛应用的一项重要技术。对其机理的进一步研究有可能推动非常规油藏开发的发展。在这项研究中，先前获得的实验数据，包括表面裂缝图像和流体压力曲线，被用于建模和比较。采用数字岩心重建和有限离散元相结合的方法，提出了一种基于压裂后岩面草图的裂缝地质模型建模过程。根据试样表面断口形貌建立二维模型。通过流体压力曲线和物理实验中获得的表面裂缝形态同时验证了这些数值模型的可行性。分析了水力压裂过程中裂缝形态的演变。模拟结果表明：（1）本研究的模拟方法比页岩水力压裂更适合煤水力压裂的模拟；(2) 流体压力的快速上升可能伴随着微裂缝的萌生和发展，导致较大裂缝的出现；(3) 实验规模的水力压裂过程可以在煤试样中产生比页岩试样更大的最大总面积和更宽的裂缝。这表明煤水力压裂比页岩形成更复杂的裂缝；(4)当岩石弹性模量增加时，最大裂缝宽度和裂缝总面积减小，裂缝长度延长。(5) 在流体压力演化过程中，起始压力和传播压力与弹性模量正相关。本研究提出的裂缝地质模型为模拟中的裂缝重建提供了直接指导。此外，研究成果可为岩石非均质性影响下水力压裂演化研究提供指导。本研究提出的裂缝地质模型为模拟中的裂缝重建提供了直接指导。此外，该研究成果可为岩石非均质性影响下水力压裂演化研究提供指导。本研究提出的裂缝地质模型为模拟中的裂缝重建提供了直接指导。此外，研究成果可为岩石非均质性影响下水力压裂演化研究提供指导。