When a hydraulic fracture intersects a natural fracture in 3D space, even if the conditions for direct crossing in 2D are not met, the hydraulic fracture can still "bypass" the natural fracture by propagating through the rock medium surrounding the natural fracture. We have investigated conditions under which a hydraulic fracture intersects a smaller natural fracture oriented perpendicular to the hydraulic fracture, and find in this reduced-order geometry that if the natural fracture only covers part of the fracturable domain height and is not filled with a tough cementitious material, the result will be an intersection geometry identical to that of a direct crossing. For the scenario with tough cementitious filling and moderate rock-filling interface strength, we study the development of tensile stress in the filling by modeling a laboratory experiment and extend the model to field-scale. The results show that as long as the cementitious material is relatively thin and the interfaces between it and the rock matrix have moderate frictional strength, sufficiently high tensile stress always develops during the bypassing process to break the filling material, also creating an intersection geometry identical to direct crossing.
Natural rock formations are ubiquitously fractured, and the intersections between a propagating hydraulic fracture and natural fractures play a very important role in determining the connectivity of the stimulated fracture network. The intersecting process between a hydraulic fracture and a natural fracture has been extensively studied in the literature [1-3], and various criteria concerning whether the hydraulic fracture will cross, be arrested by, or be offset by the natural fracture have been developed. These studies were mostly carried out in the two-dimensional (2D) space. It was realized, more recently, that certain intersection modes, such as bypassing, which we describe in the next section, are unique to 3D space and inapplicable to 2D. Using a fully coupled 3D model for hydraulic fracturing, the current study investigates the fundamental mechanism of bypassing and the conditions under which it takes place.