Discrete element method simulation of competitive fracture propagation in staged multi-cluster fracturing in shale oil reservoirs

IF 3.7 2区工程技术 Q3 ENGINEERING, ENVIRONMENTAL

Bulletin of Engineering Geology and the Environment Pub Date : 2024-09-17 DOI:10.1007/s10064-024-03897-2

Tao Huang, Ying Zhong, Qiuhang Mou, Jianlin Li, Yaohui Yan, Hao Zhang

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Abstract

Hydraulic fracture dynamics are complex due to interactions with geological features such as bedding, joints, and microcracks, which complicate multi-cluster fracking processes. This study employs a discrete element method-based numerical simulation to investigate competitive fracture propagation in multi-cluster fracking of laminated shale, focusing on how perforation cluster settings influence fracture geometry in layered formations. Additionally, considering the prevalent high-angle natural fractures (NFs) in continental shales, the research examines the competitive propagation of multiple hydraulic fractures within these NF zones. Fracture propagation near certain perforation clusters exhibits unevenness, resulting in diverse final fracture geometries due to competitive propagation effects. A greater number of clusters lead to more diverse fracture patterns, while larger cluster spacing reduces stress interference during multi-fracture propagation. Varied fracture shapes may result from stress disruptions that unevenly affect adjacent fractures, causing early termination in some and reducing cluster efficiency. For more than five clustered stages, refracturing with temporary diversion is recommended to enhance cluster efficiency. Furthermore, the reservoir zone after multi-cluster fracturing features complex fractures near the well (Area I) and simpler ones farther out (Area II). Proximity to NFs enhances complexity near the well but inhibits hydraulic fracture propagation farther from the wellbore. Therefore, designing reasonable cluster spacing based on the reservoir’s permeability and drainage radius is essential for maximizing the pay zone of Areas I and II. This research elucidates competitive fracturing dynamics in multi-clustered laminated shale reservoirs, informing the theoretical basis for reservoir unit division and providing foundation for further optimized development strategies.

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离散元法模拟页岩油藏分阶段多簇压裂中的竞争性裂缝扩展

由于与地质特征（如垫层、节理和微裂缝）的相互作用，水力压裂动力学非常复杂，这使得多簇压裂过程变得复杂。本研究采用基于离散元法的数值模拟来研究层状页岩多簇压裂中的竞争性裂缝传播，重点关注射孔簇设置如何影响层状地层中的裂缝几何形状。此外，考虑到大陆页岩中普遍存在的高角度天然裂缝（NFs），该研究还考察了这些 NF 区域内多条水力裂缝的竞争性传播。由于竞争性传播效应，某些射孔簇附近的裂缝传播表现出不均匀性，导致最终裂缝几何形状多样化。射孔簇数量越多，断裂形态越多样化，而射孔簇间距越大，则可减少多断裂传播过程中的应力干扰。由于应力干扰对相邻断裂的影响不均，可能导致断裂形状的多样性，从而造成部分断裂提前终止，降低集群效率。对于五个以上的集束阶段，建议采用临时分流的方式进行压裂，以提高集束效率。此外，多簇压裂后的储层区在油井附近（I 区）具有复杂的裂缝，而在较远的地方（II 区）则具有较简单的裂缝。靠近净裂缝会增加井口附近的复杂性，但会抑制水力压裂在井口以外的传播。因此，根据储层的渗透率和排水半径设计合理的簇间距，对于最大限度地扩大 I 区和 II 区的有效区域至关重要。该研究阐明了多簇层状页岩储层中的竞争压裂动力学，为储层单元划分提供了理论依据，并为进一步优化开发战略奠定了基础。

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来源期刊

Bulletin of Engineering Geology and the Environment 工程技术-地球科学综合

CiteScore

7.10

自引率

11.90%

发文量

445

审稿时长

4.1 months

期刊介绍： Engineering geology is defined in the statutes of the IAEG as the science devoted to the investigation, study and solution of engineering and environmental problems which may arise as the result of the interaction between geology and the works or activities of man, as well as of the prediction of and development of measures for the prevention or remediation of geological hazards. Engineering geology embraces: • the applications/implications of the geomorphology, structural geology, and hydrogeological conditions of geological formations; • the characterisation of the mineralogical, physico-geomechanical, chemical and hydraulic properties of all earth materials involved in construction, resource recovery and environmental change; • the assessment of the mechanical and hydrological behaviour of soil and rock masses; • the prediction of changes to the above properties with time; • the determination of the parameters to be considered in the stability analysis of engineering works and earth masses.