Rock anisotropy promotes hydraulic fracture containment at depth

TL;DR

This study shows that rock anisotropy significantly influences hydraulic fracture propagation, promoting vertical containment in sedimentary basins, with fracture energy dissipation playing a key role in fracture shape and elongation.

Contribution

It demonstrates through experiments and simulations that rock anisotropy and energy dissipation ratios control hydraulic fracture elongation and containment.

Findings

Anisotropic rocks cause fractures to elongate more in the bedding-parallel direction.

Fracture energy dominance leads to more elongated fractures.

Viscous energy dissipation results in more circular fractures.

Abstract

We report laboratory experiments and numerical simulations demonstrating that the anisotropic characteristics of rocks play a major role in the elongation of hydraulic fractures propagating in a plane perpendicular to bedding. Transverse anisotropy leads to larger hydraulic fracture extension in the parallel-to-bedding/divider direction compared to the perpendicular-to-bedding/arrester direction. This directly promotes vertical containment of hydraulic fractures in most sedimentary basins worldwide even in the absence of any favorable in-situ stress contrasts or other material heterogeneities. More importantly, the ratio of the energy dissipated in fluid viscous flow in the fracture to the energy dissipated in the creation of new surfaces is found to play a critical role on fracture elongation, with fracture-energy dominated hydraulic fractures being the most elongated while the viscous dominated ones remain more circular. These results open the door to a better engineering and control of hydraulic fractures containment at depth in view of the competition between material anisotropy and injection parameters (fluid viscosity and rate of injection).