INFLUENCE OF INELASTIC ROCK BEHAVIOR IN HYDRAULIC FRACTURING

This paper examines the importance of different non-linear mechanisms, such as plastic yielding, rock dilation, cohesive zone and fluid-lag on a hydraulic fracture propagating in a low permeability formation. R ock is modelled by the elastoplastic constitutive equations of Mohr-Co ulomb flow theory of plasticity for cohesive-frictional, dilatant mate rial. The fluid flow is modelled by lubrication theory and the constan t velocity flow assumption. A cohesive crack model which takes into ac count the softening behaviour that most rocks exhibit in the post-fail ure regime is employed as the propagation criterion. The problem is so lved numerically by the finite element method. It is shown that plasti c yielding, which leads to rock dilation, results in a fracture with s ignificantly greater opening and therefore a smaller dry zone than the elastic fracture.