During the fracturing stimulation of unconventional oil and gas reservoirs, such as shale, the combined effects of stress interference and reservoir heterogeneity often prevent multi-cluster fractures from propagation uniformly, resulting in a limited stimulated reservoir volume. Wellbore temporary plugging is a key method for effectively promoting balanced fracture propagation. However, owing to an insufficient understanding of its core process, that is, the migration and sealing mechanisms of ball sealers within the wellbore, field wellbore temporary plugging efficiency is generally low, severely constraining the efficient development of shale gas. To address this, the study improved the physical model of wellbore temporary plugging and systematically investigated the migration and sealing behaviors of ball sealers among different perforation clusters within a fracturing stage using a coupled CFD–DEM approach. The mechanical mechanism governing ball sealing was revealed, and the key influencing factors were identified. The study found that the successful sealing of a ball sealers requires three basic conditions: the ball must be located within streamlines directed toward the perforation, possess relatively low inertia, and experience a net holding force at the perforation that exceeds the failing force. Parametric analysis showed that the effects of the perforation-to-ball diameter ratio and perforation cluster inlet flow rate on sealing efficiency followed a non-monotonic trend, first increasing and then decreasing. In contrast, an increase in the single-cluster perforation flow ratio ( Fr ) consistently enhanced the sealing efficiency. Through extensive orthogonal simulations, this study established a sealing chart for ball sealers and identified the optimal parameter combination: a perforation-to-ball diameter ratio between 0.83 and 0.99, a perforation cluster inlet flow rate controlled within 4–7 m 3 /min, and the use of mixed‑density ball sealers with specific ratios (low: medium: high = 4:3:3, 2:3:5, or 2:4:4). Furthermore, the research indicates that ball sealers seal more readily in perforation clusters closer to the toe of the fracturing stage. By employing a staged injection strategy, the sealing location can be effectively shifted toward the heel, thereby significantly improving the overall sealing efficiency. This optimized approach has demonstrated notable success in field applications in the Weiyuan shale gas block of Sichuan Basin: the plugging pressure response increased by 4–9 MPa, and gas well production rose substantially. This study not only deepens the understanding of wellbore temporary plugging mechanism but also provides a reliable theoretical foundation and engineering guidance for optimizing diversion‑fracturing design and improving the stimulation effectiveness of the shale gas reservoirs.
Lu et al. (Thu,) studied this question.
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