A finite difference method (Itasca Flac2D) has been applied to study a horizontal borehole developed through a shale formation during hydraulic fracturing. The structural impact of differential internal fluid pressures on the borehole periphery has been studied utilizing the numerical method. The research is focused on the effect of critical parameters associated with the hydraulic fracturing on the largest principal stress and differential principal stresses in the rock. According to Coulomb’s criterion, failure occurs when the maximum principal stress reaches the ultimate strength of the material for simple tension. Based on this theory, the largest principal stress will initiate cracks in the rock and lead to the failure of rock mass. The goal was to observe the effect of borehole radius, internal injection pressure, and K (horizontal stress/vertical stress), on the induced maximum principal stress and differential principal stress. Largest principal stress is considered one of the key factors to initiate fractures in the rock. It was observed that increasing internal pressure, borehole radius, and K will significantly increase the induced maximum principal stress and differential principal stresses around the borehole.
Hydraulic fracturing is a common method that has been used in mining, petroleum and geotechnical engineering for several years. It is a process of initiating and propagating fracture in the subsurface rock by utilizing a pressurized fluid. Over the past decade, the extraction of natural gas from shale deposits by using horizontal drilling has improved the economic situation of this technique .
Horizontal directional drilling is used in some geological settings to produce methane from a variety of shale deposits. In mining, this technology can also enhance the effectiveness of coal degasification procedures and to aid in the delineation of coal reserves. 
According to Hawkes , for petroleum applications, drilling is typically performed from a surface location. In the mining industry; however, it may be feasible to drill from either surface or subsurface locations. The basic principles of directional drilling methods in mining and petroleum applications are essentially the same, involving down-hole drive motors mounted on adjustable, bent bottom hole assemblies.