| Energy extraction from underground reservoirs is normally involved with inducing fractures in rock. The induced cracks help to increase permeability and therefore, the resource can be extracted more efficiently. In this thesis, fracture initiation and propagation around a borehole is numerically studied under plane strain condition. A bonded particle system is calibrated to simulate the mechanical behavior of Berea sandstone. There are two main sections in the thesis. Firstly, simulation of the finite specimens and numerical results are shown. Secondly, infinite specimens are modeled, and the results are reported in chapter 4. To control the material ductility, the contact points between the discrete particles are allowed to follow a linear softening behavior. The borehole is pressurized by increasing the internal pressure with the use of a packer simulated by the finite element method. The size effect on the breakdown pressure is investigated. It is demonstrated that with the increase in the specimen size, the peak pressure decreases, and this size effect is affected by material ductility. Furthermore, the borehole expansion relationship with the crack tip location is studied. Such a relationship should be important in the field operation as it can help to identify the location of the crack tip based on the borehole expansion data. It is shown that this relationship and the length of the crack at breakdown pressure are affected by the material ductility. Finally, the numerical results are compared with some cavity expansion tests results conducted on cubical Berea sandstone specimens. |
