Abstract
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.
