On the use of penny-shaped hydraulic fracture’s inlet behavior in numerical modelling and diagnostic techniques

Abstract

Penny-shaped hydraulic fracture’s propagation in impermeable rocks is controlled by two energy dissipation mechanisms:viscous flow and surface generation. At the beginning of an injection treatment, viscous flowdominates fracture’s behaviour, but as injection time progresses, surface generation becomes the main dissipationmechanism. The described behaviour involves changes in tip stress singularity’s type, making difficult the use ofstandard methods of fracture mechanics. Based in existing semi-analytical solutions for zero and large toughness,we re-examine the problem of disc-shaped hydraulic fracture propagation from the point of view of near-well zone,and we propose a new propagation condition that depends on inlet values and can be used for any propagationregime. This propagation condition was implemented in the resolution of the coupled hydro-mechanical problemshowing good agreement with other numerical solutions. Additionally, for fractures propagating into a field withvariable confining stress in which viscous flow can be neglected , we introduce a propagation condition that dependson injection pressure. We show the use of this criterion in numerical modelling and how it can be used as a tool toestimate the dimensions of generated fracture(net-pressure analysis).