ABSTRACT
Hydraulic fracturing stress measurements cannot provide the magnitude of maximum compressive stress with sufficient reliability. To overcome the defect, a new loading probe that can generate a fracture plane in any desirable direction was developed by Serata Geomechanics Incorporation (1996). The authors numerically calculated a borehole wall stress condition induced by borehole pressurization using Serata probe. In spite of taking the calculated wall stress condition induced by Serata probe, the measured stresses in 600 mm-cubic specimens on which biaxial outer loads were applied using flatjacks were always almost twice larger than the actual applied pressures. On the cause, from simulation of p–δ (pressure-deformation) curves, it was elucidated that we are apt to read about twice of real re-opening pressure from gradient change of the measured p–δ curve. Thus, it was essential to develop a method to detect the point at the moment of fracture re-opening for the method.
