Variation of the Least Principal Stress with Depth and Its Effect on Vertical Hydraulic Fracture Propagation During Multi-Stage Hydraulic Fracturing

Knowledge of the least principal stress within, above and below producing intervals is essential for determining fracturing procedures that limit vertical propagation of hydraulic fractures to the intended range of depths. To better understand the cause of varying stress magnitudes in formations adjacent to unconventional reservoirs, we have combined laboratory studies of viscoplastic creep with numerical modeling utilizing in an attempt to match a profile of least principal stress measurement with depth in an actual case study. Creep experiments were conducted on core samples from different depths of a shale play in which Diagnostic Fracture Injection Tests (DFITs) were performed to determine the least principal stress. A power law creep model was used to fit the experimental data. The least principal stress was calculated from numerical modeling with a power law creep law using Abaqus. The calculated least principal stresses were found able to match the relative change of the observed stress magnitudes indicating that the variation of the least principal stress is controlled by varying amounts of viscoplastic stress relaxation. We demonstrate how the observed variations of the least principal stress with depth have an important influence on vertical hydraulic fracture propagation.