Experimental Investigations of Hydraulic Fracturing Propagation in Multi-layer Formation

Hydraulic fracturing as a method for reservoir stimulation depends on the properties of the media that fracture propagates in it. Discontinuities in the media and their mechanical properties greatly affect the geometry and propagation of hydraulic fractures. In this research، the interaction between the hydraulic fractures with the media layers interface، fracture propagation pattern and termination in multi-layered media were investigated. The true tri-axial cell was utilized to conduct experimental tests on cube multi-layered samples with discontinuities. The tests were aimed to investigate propagation of fractures from soft to stiff، stiff to soft media and also the effect of elastic properties of rocks in hydraulic fracturing. Results showed that the condition of discontinuities (healed، open or filled) and elastic properties of the layers influences the geometry and propagation pattern of hydraulic fractures. In the block with the bonded interfaces، the fracture propagates and interacts with the interfaces، then penetrates in the adjacent layers. However، for the block with unbonded interfaces the fracture propagates from the borehole up to the interface، then after filling the interface with the fluid the new fracture will propagate in the adjacent blocks. In sample where the interface was filled، the fracture propagation was terminated and then the fluid started to leak off in the interface. The results also show when the fracture reaches the interface، the pressure increased immediately and more pressure is needed for fracture propagation across the interface. In comparison between the length and width of fractures in soft and stiff layers، the study displays that the fracture width and its penetration length in soft layers are greater than those in stiff layers.