Deflection behaviours and fractal morphology of hydraulic fractures meeting beddings and granules with variable geometrical configurations and geomechanical properties
Yongliang Wang, Xuguang Liu, Nana Liu, Juan Wang
Abstract
Purpose The morphology of hydraulic fractures is mainly affected by deflection behaviours of fractures meeting embedded heterogeneous and discontinuous geological structures, such as the beddings and granules. Evaluating the propagation behaviours (deflection, intersections, penetration and arrest) and morphology of hydraulic fractures is a key scientific issue to control and optimize the fracturing effects. It is urgent to quantitatively investigate the deflection behaviours and quantitative morphology of hydraulic fractures in heterogeneous rock mass and analyze the influences of heterogeneity on fracturing effects. Design/methodology/approach To investigate the deflection behavior and fractal morphology of hydraulic fractures meeting bedding and granules, the numerical models and cases with different geometrical configurations and geomechanical properties are proposed. Based on the combined finite element–discrete element–finite volume method and fractal characterization method, the fracture deflection and quantitative fractal morphology of hydraulic fractures considering the influences of beddings and granules are investigated and analyzed. Findings The fractal dimension for the cases of bedding dip angle β = 45° is smaller than that under β = 0° and 90°; this is because the hydraulic fracture propagation is influenced by the bedding plane, resulting in deflection and propagation along the bedding plane, which affects the degree and complexity of hydraulic fracture network. The comprehensive enhanced geomechanical properties (Young’s modulus, tensile strength and cohesion) in bedding geomaterials of the bedding planes hinder the propagation of hydraulic fractures, leading to a decrease in the complexity of the hydraulic fracture network and the fractal dimension; in details, the Young’s modulus is, the more the number of deflections and branches of fractures is, and the more complex the morphology is; the tensile strength and cohesion increase the strength of the bedding planes, which leads to many penetrations of fractures and reduces the complexity and fractal dimension of fracture network. The smaller the granule size of different granule configurations under the same geomechanical properties, the larger the fractal dimension, indicating that the small granule size increases the probability of fracture deflection and complexity of the fracture network. As the geomechanical properties (Young’s modulus, tensile strength and cohesion) of the granules increase for improving their stiffness and strength, it can be seen that the fractures are prone to be influenced by the granules, resulting in many deflections and branches and lager fractal dimension. Originality/value The investigation conclusions of fluid-driven fracture propagation with different geometrical configurations and geomechanical properties of beddings and granules can provide theoretical guidance for efficient and accurate evaluation of fracture propagation behaviours and control and optimization of fracturing effects in practical engineering in heterogeneous reservoirs.