Elongated hydraulic fracture emerging from layers of alternating fracture toughness

Whether used to enhance the hydrocarbon production from low permeability rocks or to measure the minimum in-situ principal stress in rock formations, height growth of a hydraulic fracture above the formation of interest is a key metric for the design of successful hydraulic fracture applications. If the confining stress variation between rock layers represents one of the main reasons for fracture containment at depth, a contrast of fracture toughness can also lead to fracture containment. Fracture toughness contrasts are presents at different scales. They are due to lithological changes at the scale of layers, but they also appear at smaller scales, down to the size of bedding planes. The interaction of a hydraulic fracture with a repetitive sequence of multiple layers of different fracture toughness can ultimately lead to the emergence of an elongated fracture or, alternatively, to the propagation of an elliptical-like fracture with a fixed aspect ratio. Combining theory and simulations, we study the possible emergence of an elongated hydraulic fracture from layers of alternating fracture toughness considering typical hydraulic fracturing treatments as well as micro-hydraulic fracturing test cases.