Experimental study on hydraulic fracture propagation behavior of horizontal well on multilayered rock

A series of true axial hydraulic fracturing experiments were conducted to understand the complex hydraulic fracture initiation and propagation behavior of multilayered rocks. Moreover, a new and convenient grid measurement method was presented to describe hydraulic fracturing effectiveness. The experimental results revealed that transverse vertical and non-planar axial fractures could be created in the hydraulic fracturing of multilayered rocks. Moreover, the fracture area scanning results by the grid measurement method match the results indicated by the traditional Geomagic method. The fracture behavior close to the layer contact determines how complex the produced fishbone structure fracture system is. Near the hole zones, secondary axial and deviated transverse fractures were found due to multiple layers. The fracture system can be managed by modifying the fracturing treatment parameters. Low-principle horizontal stress contrast and low-viscosity fracturing fluid can produce complicated fractures, and an increase in perforation numbers can make the fracture more complex and produce abnormally high breakdown pressure. Larger fracture areas benefit from high perforation rates and pump rates, but larger fracture areas may not always benefit from a decreased fracturing fluid viscosity. The breakdown pressure was the highest for the samples with two sets of oriented perforations, and the stress shadowing effect should be considered in the multiple fracture treatment. The increase in the pump rate generates a more complex fracture path in the horizontal well despite the fracturing fluid types but also yields a high breakdown pressure. The increased fracturing fluid viscosity can constrain the random fracture extension, which is beneficial for decreasing the near-wellbore tortuosity. The occurrence of shear fracture along the interface in a multilayered formation could be a risk for proppant injection and placement.