**2. Hydraulic testing of pre-existing fractures method**

Hydraulic testing of pre-existing fractures (HTPF) method provides an evaluation of the complete stress tensor (six components), independent of borehole orientation and material properties.

A portion of a borehole is closed off by use of two inflatable rubber packers adequately pressurized so that they hold on to the borehole wall (**Figure 1**). The water is pumped under continuous flow rate into the portion, gradually increasing the pressure on the borehole wall until a fracture is begun in the rock, or a pre-existing fracture is opened. Pumping is halted, allowing the interval pressure to deteriorate. Several minutes into the shut-off phase, the pressure is released and allowed to return to ambient circumstances. The pressure cycle is repetitive several times maintaining the same flow rate. Key pressure values used in the computation of the in-situ stresses are plucked from the pressure-time record. The repeated cycles deliver redundant interpretations of the key pressures. The attitude of the induced hydraulic fracture, or of the pre-existing fracture, is achieved using an

*Hydraulic Fracturing in Porous and Fractured Rocks DOI: http://dx.doi.org/10.5772/intechopen.106552*

**Figure 1.** *Typical HTPF test equipment setup.*

oriented impression packer. Hydraulic fracturing orientation is related to the directions of the principal stresses [1–15].

HTPF, tests yield an evaluation of the normal stress supported by fracture planes with different known orientations, and the complete stress evaluation results from an inversion of these results.

The main difference between HTPF and Hydraulic fracturing tests are certain assumptions made; otherwise, the process remains same. The following are certain assumptions:

