Mechanism of Sealed Wellbore Deformation and Pressure Change Induced by Propagating Hydraulic Fractures

Summary Sealed wellbore pressure monitoring (SWPM) offers a low-cost fracture diagnostic method for identifying fracture-driven interaction and nonuniform propagation of multiple fractures. Although previous studies have revealed pressure responses in sealed wellbores (SWs) induced by hydraulic fractures, current understanding remains insufficient, and reliable fracture simulation together with wellbore deformation analysis is still required to interpret SW pressure signals. To address this, we use a planar 3D multifracture propagation simulator to calculate SW deformation and pressure evolution. Using the 3D displacement discontinuity method (DDM) to compute wellbore strain by treating the wellbore as an elastic line problem, we establish a forward model and computational method to simulate volume and pressure change in a SW induced by fracture propagation during horizontal well fracturing. Through numerical simulations, we investigate the evolution of SW volume and pressure during fracture growth under varying cluster number, injection rate, well spacing, and leakoff coefficient. Our results indicate that SW volume and pressure responses induced by both single and multiple fracture propagation exhibit similar characteristics. The time when a fracture hits the SW for a single fracture can be identified precisely from the peak in the pressure change rate, which also allows us to estimate the fracture propagation average velocity. After pumping shut-in, while the direction of SW volume and pressure change remains unchanged, their rate of change reverses, and the pressure change rate effectively reflects injection dynamics. Higher injection rate and lower leakoff coefficient lead to faster fracture propagation, larger fracture length and width, and stronger amplitudes and change rates in the SW volume and pressure responses. Larger well spacing results in weaker stress disturbance signals and lower SW volume and pressure response amplitudes. When the well vertical spacing exceeds the height range of fracture propagation, the SW response becomes too weak to effectively evaluate vertical fracture propagation and fracture hit. The peak in the SW pressure change rate may slightly lag behind the time when the fracture hits the offset well for multifracture growth, a delay attributed to the superposition of strain effects from nonuniform multifracture propagation. Analysis of post-shut-in SW pressure data using the G-function demonstrates that the dp∕dG and Gdp∕dG characteristic curves can accurately determine the closure time of fractures intersecting the offset well. This study provides technical insights for interpreting SWPM signals.