Investigating Fracture Growth After Shut-In

Hydraulic fractures are often assumed to immediately stop growing once pumps are shut off after fracturing treatments. However, fluid momentum and rock properties may allow propagation to continue temporarily post-shut-in. The objective of this study is to determine if and under what circumstances fractures actually arrest after pump shut-in through numerical modeling. To address this gap, an integrated numerical model is proposed to simulate the fracture propagation process and shut-in process, which coupling the fluid flow, geomechanics, and fracture mechanics. A mathematical model estimates fracture length post-shut-in based on parameters like injection rate and fluid properties. This multifaceted modeling approach provides insights into fracture growth mechanisms once pumps are shut-in. Modeling shows fractures may continue propagating after pumps are shut-in, significantly influenced by injection rates, fluid/rock properties, and geometry. Leveraging the presented mathematical model, we can roughly see how different factors can affect the movement of the tip of a tensile fracture. Simulation results show that the presence of post-shut-in fracture propagation can lead to an 9.17% increase in fracture half-length under the model conditions. Besides, higher fluid momentum and smaller fracture volume can support the continuation of fracture propagation after the pumps are turned off. A fast and short fluid injection (injection rate and time are 0.0008 m³/s and 200 s) can lead to an 11.4% increase in fracture half-length. Then, it was also found that lower leak-off coefficients can also help improve post-shut-in fracture propagation by up to 10.18%. Neglecting this post-shut-in effect in diagnostic fracture injection tests (DFIT) could misestimate stress and rock properties. This research provides new insights on fracture growth mechanisms especially for post-shut-in, enabling better fracture control and test interpretation. This study uses numerical modeling to determine if/when fractures stop after shut-in. Results give a better understanding of post-shut-in fracture growth, improving fracture control and test interpretation.