Poroelastic concepts explain some of the hydraulic fracturing mechanisms

This paper reviews the role of coupled diffusion/deformation phenomena in the various facets associated with hydraulic fracturing: Breakdown, propagation and closure, and the assessment of these effects by means of Biot's linear theory of poroelasticity. The poroelastic concepts are first recalled and emphasis is placed on the fundamental parameters needed. The importance of the coupling terms in the elasticity and diffusion equations is also stressed. The general equations are then simplified for two particular applications: One-dimensional column and radi a 1 symmetry. It is then shown that the reservoir history as well as the percolation occurring prior to hydraulic fracture initiation affects the breakdown pressure value. Poroelastic models also explain the decrease of propagation pressure with pore pressure, as has been often reported in the field. Finally, the fracture closure is considered and the coupling mechanisms clearly demonstrate the width decrease as well as the increase of shut-in pressure with time.