Abstract
Simulation of fracture propagation with FEM method generates the need of re-meshing to provide more accurate results. This raises a question of determining the direction and criterion of mesh modification. In the case of general-purpose CAE-packages, we deal with a stationary mesh, and the fracture path is usually represented as a chain of elements with degraded properties. The algorithm proposed in this paper is based on the ANSYS Mechanical APDL language for stepwise geometry reconstruction and mesh modification in accordance with the current configuration of a growing fracture and provides a more accurate description of its shape. The fracture propagation process is divided into stages. Each subsequent stage differs from the previous one by the fracture shape modified due to the crack length increment in the calculated direction. To check the adequacy of the model, an experiment on fracture propagation in glass specimens with an initial notching under uniaxial compression was performed. The laboratory experiments were carried out to determine the fracture toughness of rocks. The developed numerical model has been used to solve the problem of re-fracturing for different stress anisotropy in the oil-bearing rock formation.
Highlights
I n the last few years the effect of the directional hydraulic re- fracturing (HF) on the stress-strain state of oil-bearing rock formations has been extensively discussed in the scientific and engineering literature
As it is seen from the figure, with increasing width of the primary fracture opening, the secondary HF practically does not change its direction towards the highest compressive stress even at large stress anisotropy and grows in the direction perpendicular to the primary fracture
An increase of the opening width of the primary fracture In the presence of all these factors the effect of the secondary HF will be maximal because its realization opens up the maximum of non-depleted zones of the oil pool
Summary
I n the last few years the effect of the directional hydraulic re- fracturing (HF) on the stress-strain state of oil-bearing rock formations has been extensively discussed in the scientific and engineering literature. Work [8] offers a 3Dmodel to describe the growth of a crack in machine elements, which was implemented numerically as a finite element ZENCRACK program (developed by the company Zentech International Limited) applied in fracture mechanics Another example of adaptive remeshing to trace crack propagation is the Franc3D program (FRacture ANalysis Code for 3D), which is based on the boundary element method. The possibilities of this package are demonstrated in work [9] in the context of the problem of crack growth in the gear wheel. STRESS FIELD AFTER FORMATION OF THE PRIMARY HF FRACTURE AND INITIATION OF THE SECONDARY
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