Recently, hydraulic fracturing technique is being used worldwidely to determine the in-situ stress in the earth's crust. Most of the works deal with hard impermeable rock masses and therefore the theories are developed to suit for such kind of rock. However, there are so many cases where the rock masses are saturated and permeable. They are usually soft and weak. The in-situ stress determination in such soft rock mass has eagerly been searched for, but an effective method has not been invented yet.
In this paper, the result of the feasibility study for the hydraulic fracturing technique on the soft rock (mudstone) was reported. The mechanical properties and the behavior of soft rock during injection of pressurized water were investigated. Vertical and horizontal fractures were created in a modified triaxial cell under various stress conditions. The flow rate and the pressure-increase rate in a drilled hole were found to be very influential to the fracture orientation. Also, the application of this hydraulic fracturing technique to the field problems was briefly discussed.
