**3.2 Data Interpretation code GENSIM**

Impression packer tests suggest that in many cases hydraulic testing had been carried out along differently orientated fractures in the rock mass. The interpretation of these data requires sophisticated methods like the GENSIM rather than simple classical hydrofrac hypothesis.

The GENSIM algorithm assumes that the vertical is a principle stress axis and the vertical stress is equal to the weight of overburden rock stress. Stress–depth

dependence is neglected within the program through which GENSIM is limited to short depth intervals

$$
\sigma\_{\rm h} = (P\_{\rm si} - n\mathcal{Z}.\sigma\_{\rm V})/(m\mathcal{Z} + l\mathcal{Z}.\sigma\_{\rm H}/\sigma\_{\rm h}) \tag{1}
$$

Where, *l*, *m*, *n* in the equation are the cosines of the direction of the induced fracture planes obtained during study; *P*si is the shut-in pressure in MPa obtained from pressure record for certain depths and *σ*H/*σ*<sup>h</sup> is the stress ratio condition which prevails in ground conditions as 1.5, 2 and 2.5 considered for determining the minor principal horizontal stress.

Results in **Table 1** were done by using shut-in pressure data as given in **Tables 2**–**4** derived from the measurements in the borehole and varying the ratio *σ*H/*σ*h and the strike direction of *σ*H in the horizontal plane.

The stress gradient is plotted to observe any induced stress due to excavation or topography of rock cover (**Figure 16**). It is clearly understood that results determined are free from any influence.


**Table 1.**

*Stress tensors as evaluated at various locations.*


#### **Table 2.**

*Fracture orientation data obtained from BH-1 and BH-2 with high flow rate-15 l/min (location: Powerhouse upstream; Teesta stage-IV Hydroelectric project West Bengal).*


#### **Table 3.**

*Fracture orientation data obtained from BH-5 and BH-6 with high flow rate-15 l/min (location: intake drift; Teesta stage-IV Hydroelectric project West Bengal).*

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


**Table 4.**

*Fracture orientation data obtained from BH-3 and BH-4 with high flow rate-15 l/min (location: powerhouse downstream; Teesta stage-IV Hydroelectric project West Bengal).*

**Figure 16.** *Stress gradient in fracture rock mass.*
