Determination of Minimum pressure required for initiation of crack growth in hydraulic fracturing process

The hydraulic fracturing is a suitable operational method for stimulating and increasing the productivity of oil and gas wells. In this method, a liquid is pumped to the wellbore until creation and then propagation of a fracture in the wall of wellbore. The aim of this paper is to determine the minimum pressure required for developing a hydraulic fracture from an initial perforation in the wall of well. The evaluation of the minimum pumping pressure is an important task for performing an optimum and successful hydraulic fracture operation. Since the hydraulic fracturing is essentially a process of crack growth in the wellbores and in the reservoir formations, it is preferred to investigate this method using the concepts of rock fracture mechanics. In this paper, the minimum pumping pressure diagrams have been presented for different conditions of a wellbore during the hydraulic fracturing process. In order to obtain the diagrams, several 3D finite element models of the well having an initial semi circular perforation were analyzed under different loading conditions and the influence of affecting parameters such as the in-situ stresses, the depth of initial perforation and the wellbore inclination angle on the minimum pumping pressure were investigated numerically. It is shown that the minimum horizontal in-situ stress is the most affecting parameter on the required pumping pressure at great depths. The pumping pressure increases by increasing the minimum in-situ stress. Meanwhile, inclined wells require smaller pumping pressures in comparison with the vertical wellbores.