The influence of pumping parameters in fluid-driven fractures

In the present work we investigate the main pumping parameters that influence a fluid driven fracture in both cohesive poroelastic and poroelastoplastic weak formations. These parameters include the fluid viscosity and the injection rate. The fracture is driven in weak permeable porous formation by injecting an incompressible viscous fluid at the fracture inlet assuming plane strain conditions. Fluid flow in the fracture is modeled by lubrication theory. Pore fluid movement in the porous formation is based on the Darcy law. The coupling follows the Biot theory while the irreversible rock deformation is modeled with the Mohr-Coulomb yield criterion with associative flow rule. Fracture propagation criterion is based on the cohesive zone approach. Leak-off is also considered. The investigation is performed numerically with the finite element method to obtain the fracture length, opening and propagation pressure vs time. We demonstrate that the pumping parameters are influencing the fracture geometry in weak formations through the diffusion which creates back stresses and large plastic zones. It is shown that the back stresses act as a barrier and larger net pressures are needed to propagate the fracture. This effect in the poroelastoplastic formation is responsible for the creation of larger plastic zones. These influences for large viscosity or high injection rates result in larger fracture profiles and propagation pressures. These findings may explain partially the discrepancies in net-pressures between field measurements and conventional model predictions.