Simulation of Hydraulic Fracturing Method with Cohesive Crack Model

Hydraulic fracturing defined as a process in which a hydraulic loading caused by fluid injection in a part of wells result fracture propagation in the rock. The main purpose of this research is simulation of hydraulic fracturing based on the concepts of Finite Element Method (FEM) and parameters affecting it. For this goal, ABAQUS software has been used to examine hydraulic fracture initiation pressure in a simulated petroleum reservoir in which the cohesive elements theory with traction-separation law existed. To do so, a cohesive crack model has been introduced, govern equations has been discussed and then the way of building a poroelastic three-dimensional model with cohesive elements is described. The results show that the fracture pressure obtained from FEM model is in agreement with the analytical values. Fluid leak- off rate diagram shows three different time steps that the first two steps represent the expression of leak- off jump and third stage shows dynamic leak- off. Fluid pressure changes along the fracture shows a decreasing trend as the fluid pressure is lower than the initial pore pressure due to the phenomenon of fluid-lag at the fracture tip. Finally, a sensitivity analysis was conducted on a number of parameters on the fracture initiation pressure and results show increasing in all parameters except for Poisson's ratio, led to an increase in fracture initiation pressure. Also, the sensitivity function calculations for each of the parameters show that Young's modulus and leak-off coefficient have the highest and lowest effect on fracture initiation pressure, respectively.