Purpose

Optimized three-dimensional (3D) fracture networks are crucial for multistage hydrofracturing. To better understand the mechanisms controlling potential disasters as well as to predict them in 3D multistage hydrofracturing, some governing factors, such as fluid injection-induced stratal movement, compression between multiple hydraulic fractures, fracturing fluid flow, fracturing-induced microseismic damaged and contact slip events, must be properly simulated via numerical models. This study aims to analyze the stratal movement and microseismic behaviours induced by multistage propagation of 3D multiple hydraulic fractures.

Design/methodology/approach

Adaptive finite element–discrete element method was used to overcome the limitations of conventional finite element methods in simulating 3D fracture propagation. This new approach uses a local remeshing and coarsening strategy to ensure the accuracy of solutions, reliability of fracture propagation path and computational efficiency. Engineering-scale numerical models were proposed that account for the hydro-mechanical coupling and fracturing fluid leak-off, to simulate multistage propagation of 3D multiple hydraulic fractures, by which the evolution of the displacement, porosity and fracture fields, as well as the fracturing-induced microseismic events were computed.

Findings

Stratal movement and compression between 3D multiple hydraulic fractures intensify with increasing proximity to the propagating fractures. When the perforation cluster spaces are very narrow, alternate fracturing can improve fracturing effects over those achieved via sequential or simultaneous fracturing. Furthermore, the number and magnitude of microseismic events are directly proportional to the stratal movement and compression induced by multistage propagation of fracturing fracture networks.

Originality/value

Microseismic events induced by multistage propagation of 3D multiple hydraulic fractures and perforation cluster spaces and fracturing scenarios that impact the deformation and compression among fractures in porous rock matrices are well predicted and analyzed.

中文翻译：

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三维多级水力裂缝多级扩展引起的地层运动和微地震行为的自适应有限元-离散元分析

目的

优化的三维 (3D) 裂缝网络对于多级水力压裂至关重要。为了更好地理解控制潜在灾害的机制并预测 3D 多级水力压裂中的潜在灾害，一些控制因素，如流体注入引起的地层运动、多条水力裂缝之间的压缩、压裂液流动、压裂引起的微地震损伤和接触滑移事件，必须通过数值模型正确模拟。本研究旨在分析由 3D 多条水力裂缝多级传播引起的地层运动和微地震行为。

设计/方法/方法

自适应有限元-离散元方法用于克服传统有限元方法在模拟3D裂缝扩展方面的局限性。这种新方法使用局部重新网格化和粗化策略来确保解的准确性、裂缝传播路径的可靠性和计算效率。提出了考虑水力耦合和压裂液泄漏的工程规模数值模型，以模拟 3D 多条水力裂缝的多级扩展，由此位移、孔隙度和裂缝场的演变以及压裂计算了诱发的微地震事件。

发现

3D 多条水力裂缝之间的地层运动和压缩随着与扩展裂缝的接近程度的增加而加剧。当射孔簇空间非常狭窄时，交替压裂可以改善通过顺序或同时压裂实现的压裂效果。此外，微地震事件的数量和幅度与压裂裂缝网络的多级传播引起的地层运动和压缩成正比。

原创性/价值

很好地预测和分析了由 3D 多个水力裂缝和射孔簇空间的多级传播引起的微地震事件以及影响多孔岩石基质中裂缝之间变形和压缩的压裂场景。