Abstract: To study absolute rock stress measurement under different fracture media, by using large chamber true triaxial hydraulic-pressure fracture simulating system, a hydraulic fracturing experiment in lab is carried out with 400 mm×400 mm× 400 mm granite specimen on effect of the water and the relative densities of 1.1 g/cm3, 1.2 g/cm3, 1.3 g/cm3, 1.4 g/cm3 respectively, the continuous pressure-time curves are obtained. By using 6 kinds of methods, closure pressure points on pressure-time curve are distinguished; 4 kinds of methods, for example single tangent, are consistent with actual situation through contrasting the actual minimum horizontal principal stress ( 5 MPa). Considering the effect of experimental flexibility, the measured reopening pressure and theoretical reopening pressure are contrasted. Finally, the pressure of extended rock fissures in continuous pumping pressure is analyzed. The experimental results show that the slurry relative densities of 1.1 g/cm3, 1.2 g/cm3 have little effect on pressure characteristic parameters; and its error is no more than 1 MPa; the slurries with relative densities of of 1.3 g/cm3, 1.4 g/cm3 have great effect on values of pressure characteristic parameters. The experimental results have an important guiding meaning for application of hydraulic fracturing technology to measurement of absolute stress under different fracture media.

Key words: hydraulic fracturing, laboratory experiment, different fracture medium, pressure characteristic parameter