**6. Hydraulic fracturing in porous rocks**

Hydraulic fracturing method is the accepted technique for measurement of insitu stresses in hydroelectric projects and in metalliferous mining projects in India and abroad. But its use in coal mines is limited to a few British and Australian coal mines. This is mainly because of the occurrence of porous rocks in coal mines in India and elsewhere.

Scanty literature is available for this type of studies as this procedure of experiments is still in the budding stage. Hence literature references have not been elaborately quoted since it was not an objective of this work to critically compare aspects of our experience with those of other works. The method used in the present study is described here in its near original form in order to place on record the experience gained.

#### **6.1 High viscous fluid technique in porous rocks**

The porosity has major effects on hydraulic fracturing technique which results in fracture deviation away from the actual orientation (**Figures 18** and **19**). High viscous liquid instead of water is used for pressurization during hydraulic fracturing, but the influence by using viscous liquid on the stress is not known (**Figures 20** and **21**). The results (**Tables 10**–**12**) are validated with overcoring technique that is applicable in porous rocks. Over coring method does not get influenced from the presence of porosity in the rock mass [2, 7, 14, 19].

**Figure 18.** *Hydraulic fracturing test with normal flow rate in porous rocks.*

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

#### **Figure 19.**

*Hydraulic fracturing test with high flow rate in porous rocks.*

#### **Figure 20.**

*Pressure drop for low viscous oils (less than 200 cP).*

#### **Figure 21.**

*Pressure-time record obtained using high viscous liquid (ISO VG 320 oil).*


#### **Table 10.**

*Fracture orientation data obtained from borehole at KTK 8 incline, Singareni Collieries Company Ltd. Telangana.*
