Hydraulic Fracture Closure Revealed Under Controlled Laboratory Condition

This study observed hydraulic fracture propagation, arrest, and closure in permeable rocks. The experiment was conducted on a Molasse sandstone block in a true triaxial state of stress. The study monitored fracture opening at the wellbore and fluid pressure measurements to understand hydraulic fracture propagation and closure. The study used pressure derivatives to the square root of shut-in time to identify fracture closure, which is consistent with recent theoretical estimates. The behavior of width and pressure upon closure aligned with theoretical expectations. The scaled opening versus reverse time and scaled pressure over the square root of reverse time exhibited linear behavior, as predicted by theory. Furthermore, the study discovered an irreversible residual opening at the wellbore even after complete fracture closure. This opening may be due to a small amount of shear slip/fracture mixed modality, which could cause misalignment of the fracture surfaces' asperities at closure. The magnitude of this opening is dependent on the Molasse sandstone grain size.