Water injection laboratory experiments in weak, poorly consolidated sandstones show evidence that the peak injection pressure is much larger than the one predicted by the Haimson-Fairhurst criterion. A model based on poroelasticity, fracture mechanics, and lubrication theory is constructed to simulate the laboratory experiments. It aims at computing the propagation of a bi-wing hydraulic fracture from a borehole with increasing injection rate, until the crack reaches the boundary of the sample. The model is applicable to situations for which the pore pressure field reaches steady-state quasi-instantaneously when changing the injection rate, on account of the large permeability of these rocks. Two asymptotic regimes of solution are found: (i) a rock-flow regime where the induced fracture is hydraulically invisible, and (ii) a fracture-flow regime where the fluid penetrates the rock via the crack. In the rock-flow regime, fracture propagation is stable, i.e., the borehole pressure increases with the injection rate, while in the fracture-flow regime, the reverse is true. It is therefore concluded that the peak injection pressure reflects a transition between two flow regimes, rather than breakdown.
|Original language||English (US)|
|State||Published - 2020|
|Event||54th U.S. Rock Mechanics/Geomechanics Symposium - Virtual, Online|
Duration: Jun 28 2020 → Jul 1 2020
|Conference||54th U.S. Rock Mechanics/Geomechanics Symposium|
|Period||6/28/20 → 7/1/20|
Bibliographical noteFunding Information:
The authors acknowledge the Theodore W. Bennett chair in Mining Engineering and Rock Mechanics for support of this research. They also benefited from valuable discussions with Robert Eve and Robert Heller of BP Petroleum about the experimental program.
© 2020 ARMA, American Rock Mechanics Association
Copyright 2020 Elsevier B.V., All rights reserved.