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Interference Behaviour between Bedding Planes and Hydraulic Fractures and Its Influence on the Complex Fracture Network in Shale
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DOI：10.1007/s00603-024-04167-z.png)
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Abstract
En 中文
The development of bedding planes was a prominent feature of shale, and the stress interference between hydraulic fractures and bedding planes played a key role in forming fracture networks. Elucidation of the mechanism of the mutual interference between hydraulic fractures and bedding planes could help improve the fracturing technology of the shale fracture network. To simultaneously reflect the roles of both hydraulic fractures and bedding planes in the model, a series of large-size three-dimensional numerical models were established in this study using the ABAQUS finite element software. The cross-cohesive unit and the pipe flow unit were employed to simulate the cross-extension of the fracture with the bedding plane and the injection of fracturing fluid into the wellbore, respectively. Moreover, the correctness of the numerical models was verified by the analytical solution of the PKN simplified fracture model. The cohesive zone model (CZM) considered the softening effect and plastic zone at the top of cracks in quasibrittle rocks (e.g. shale), obtaining a more accurate crack geometry and in-seam pressure than linear elastic fracture mechanics. The cross-cohesive unit realized different traversal morphologies of the cracks when they interacted with the bedding plane. This paper analyzed the distribution of induced stresses generated by hydraulic fractures and bedding fractures. The induced stresses generated by hydraulic fractures were concentrated at the base of hydraulic fractures, and the stress shadows at the fracture tip made it easier for hydraulic cracks to cross bedding planes; the distribution plane of induced stresses generated by bedding fractures was parallel to bedding planes, and this induced stress was an essential factor influencing the traversal morphology of fractures. The results showed that the properties of the bedding plane significantly affected hydraulic fracture propagation in the height direction and the morphology of the fracture network. On the one hand, diverting the bedding plane limited the vertical propagation of hydraulic fractures. On the other hand, the induced stresses generated by the opened bedding plane hindered the opening of subsequent bedding planes. A series of three-dimensional numerical models with multiple clusters and bedding planes considering the dynamic flow distribution and perforation friction were established.Considering the development of shale bedding, this paper focused on the influence of three bedding structural parameters, namely, bedding strength, bedding spacing and bedding density, on fracture propagation patterns.Both the interference mechanism between hydraulic fractures and bedding planes and between bedding planes themselves was revealed.
Keywords:
Shale gas
Hydraulic fracturing
Fracture interference
Multicluster hydraulic fractures
Multilayered bedding planes
Bedding spacing
Bedding density
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