Influence of the fracture process zone on fracture propagation mode in layered rocks

During the hydraulic fracturing, fractures are often kinked, blunted, or offset owing to the alternating, interbedded interfaces of diverse properties that render fracturing performance unsatisfactory. In this study, two cases (the artificial fracture perpendicular to and parallel to the bedding interfaces) were examined through three-point bending experiments on semi-circular bending (SCB) using shale specimens. The fracture process zone (FPZ) was studied based on the Digital Image Correlation (DIC) technique. The interbedded interfaces ahead of the artificial fracture tip affect the fracture propagation, with its extents are related to the bedding planes. In such conditions, the FPZ is composed of two parts: the FPZ ahead of the artificial fracture tip, and the zones of the deformed bedding interfaces distant from the artificial fracture tip. When the artificial fracture ran along the bedding interface, after peak loading, the interbedded interfaces on both sides of the main fracture undergone tensile failure. In turn, the deformation at the interbedded interfaces restricted the extension of the main fracture. The propagation mode of the hydraulic fracture accompanied by distant opening/slipping of interbedded interfaces is found remarkable in the layered reservoirs, and should be included in hydraulic fracturing designs or numerical fracturing modeling.