Analysis of Non-Planar Multi-Fracture Propagation from Layered-Formation Inclined-Well Hydraulic Fracturing

Current research shows that layered formation barriers can have a significant impact on the extension of fracture height; however, there are few studies on inclined-well near-wellbore fracture propagation shapes and penetrating patterns near the interface. We performed a true triaxial hydraulic fracturing experiment to study the layered formation of inclined-well near-wellbore and interface fracture propagation geometries influenced by formation conditions and perforation schemes. The results revealed that horizontal stress differences, perforation phase angles, borehole azimuths, and interlayer minimum horizontal in situ stress differences were the main factors that controlled the fracture propagation geometry. Under the conditions of large differences in horizontal stress, large perforation phase angles, and large angles between the borehole azimuth and the maximum horizontal in situ stress azimuth, the near-wellbore cracks presented a single main fracture with a large number of secondary fractures; in addition, the main and secondary fractures changed orientations. With moderate horizontal stress differences and less severe angle parameters, the fracture propagation geometry was simplified, forming a single main fracture. When all three parameters were small, the cracks displayed multiple main or network fractures. The surface morphology of spatial distribution was complex and the seam surface was rough. Under a crossing condition, the pattern of the penetrating fractures was highly affected by the near-wellbore fractures when the interlayer minimum horizontal in situ stress differences were small. Under large interlayer minimum horizontal in situ stress differences, the interface fractures began to deflect and generate new branches. The fluctuation and increase in fracturing pressure was caused by the dispersion of the fracturing fluid flow from multi-fractures and the large number of seam surfaces.