  We detail the energy balance of a propagating hydraulic fracture. Using the
linear hydraulic fracture model which combines lubrication flow and linear
elastic fracture mechanics, we demonstrate how different propagation regimes
are related to the dominance of a given term of the power balance of a growing
hydraulic fracture. Taking an energy point of view allows us to offer a
physical explanation of hydraulic fracture growth behaviours, such as, for
example, the transition from viscosity to toughness dominated growth for a
radial geometry, fracture propagation after the end of the injection or
transition to self-buoyant elongated growth. We quantify the evolution of the
different power terms for a series of numerical examples. We also discuss the
order of magnitudes of the different terms for a industrial-like hydraulic
fracturing treatment accounting for the additional dissipation in the injection
line.
