  Though a number of formulations have been proposed for phase--field models
for hydraulic fracture, the definition of the degraded poroelastic strain
energy varies from one model to another. This study explores previously
proposed forms of the poroelastic strain energy with diffused fracture and
assesses their ability to recover the explicit fracture opening aperture. We
then propose a new form of degraded poroelastic strain energy derived from
micromechanical analyses. Unlike the previously proposed models, our
poroelastic strain energy degradation depends not only on the phase--field
variable (damage) but also on the type of strain energy decomposition.
Comparisons against closed form solutions suggest that our proposed model can
recover crack opening displacement more accurately irrespective of Biot's
coefficient or the pore--pressure distribution. We then verify our model
against the plane strain hydraulic fracture propagation, known as the KGD
fracture, in the toughness dominated regime. Finally, we demonstrate the
model's ability to handle complex hydraulic fracture interactions with a
pre--existing natural fracture.
