The hydraulic fracturing technique is used for determining the in-situ rock stress in a plane perpendicular to borehole. This is done by application of fluid pressure (normally water) in a test section in a borehole isolated by packers until the rock fails in tension.
The fluid pressures required to generate, propagate, sustain and reopen tensile fractures in the rock are recorded as function of time, and these may be related to magnitude of the existing stress field.
Directions of measured stress are normally achieved by observing and measuring the orientation of the hydraulically induced fracture plane by the use of a so-called impression packer.
The induced hydro fracture is oriented parallel with the major secondary principal stress σH in a plane perpendicular to the borehole.
Source: Application of Rock Mechanics in underground and surface mining, Indian Bureau of mines.
