Continued Hydraulic Fracture Growth After Well Shut-In

A hydraulic fracture does not immediately stop and close at the time of well shut-in, but keeps growing and stays open for certain time after the end of the treatment. In this paper, we study the dynamics of continued hydraulic fracture propagation in rocks followed by subsequent fracture closure for different parametric regimes of fracture propagation. Because of possible deviation from a viscosity-dominated regime, we revisit the classical PKN model of hydraulic fracture by including the influence of fracture toughness of rock. That allows us to keep track of the time interplay between all volume and energy components, including viscous and surface dissipation rates. Depending on the parameters of fluid injection and rock, after the pumps are stopped, a hydraulic fracture continues to grow. After the termination of growth, the fracture stays statically open for a limited time, which is indicated by a specific signature in the wellbore pressure record. The final stage of fracture closing is associated with the heterogeneous fracture closure from the tip to inlet.