To elucidate the energy evolution and damage mechanisms of deep roadway surrounding rock subjected to principal-stress loading–unloading, conventional true-triaxial compression tests, graded loading–unloading tests along different principal-stress directions, and single-cycle loading–unloading tests were conducted on sandstone using an in-house-developed TAWZ-5000/3000 computer-controlled true-triaxial rock testing system. Based on the observed three-dimensional strain coupling, an energy-calculation framework incorporating deformation and work contributions in all three principal-stress directions was developed. Damage evolution under the different principal-stress paths was further evaluated using a dissipated-energy-based damage variable and acoustic emission (AE) monitoring. The results showed that loading–unloading along a single principal-stress direction induced strain variations not only in the cycling direction but also in the other two directions, demonstrating pronounced three-dimensional deformation coupling. Distinct hysteresis loops developed in the stress–strain curves, and their areas increased nonlinearly with increasing loading–unloading level. Under maximum-principal-stress cycling, the dissipated-energy ratio increased progressively, reflecting sustained accumulation of irreversible deformation and damage under increasing σ1. Under intermediate-principal-stress cycling, the elastic-energy ratio increased progressively while the dissipated-energy ratio remained relatively low, indicating a strong capacity for elastic energy storage. Under minimum-principal-stress cycling, dissipated energy increased at an accelerated rate, accompanied by the most pronounced post-test macroscopic cracking, indicating that repeated unloading under reduced confinement markedly promotes deterioration of rock integrity. These findings provide new insights into the path-dependent energy evolution and damage mechanisms of deep rocks subjected to excavation-induced disturbances and contribute to the stability assessment and control of deep roadway surrounding rock.
Multi-cluster hydraulic fracturing is widely used to improve reservoir contact in unconventional formations, but stage treatments commonly evolve toward uneven cluster intake. This study develops a coupled three-dimensional FEM–CZM framework linking poroelastic stress interaction, transient wellbore hydraulics, and time-dependent perforation erosion. The fracture–poroelastic–wellbore variables are solved implicitly in Abaqus/Standard, whereas perforation diameter and discharge coefficient are updated sequentially at increment boundaries through USDFLD. Component-level verification is conducted against PKN, published multi-fracture, and erosion benchmarks. The results indicate that stress shadowing is the primary mechanical selector of cluster dominance, while wellbore and perforation losses amplify the resulting flow redistribution. Perforation erosion is path-dependent rather than universally destabilizing: it amplifies the cluster accumulating the greatest velocity-squared slurry exposure, but can partially compensate a mechanically disadvantaged cluster when that cluster acquires an early hydraulic advantage. Along-well friction introduces a heel-to-toe pressure gradient, so symmetric perforation schemes need not produce symmetric intake. An initial hydraulic restriction contrast, HRC0, is introduced to compare differentiated designs. For the investigated Weiyuan-type cases, the transition toward improved allocation is bracketed between HRC0 = 0.36 and 0.50, subject to erosion and treating-pressure constraints. The framework therefore supports diagnosis-driven, non-symmetric entry design rather than a universal completion rule.
Sandstone-shale-sandstone interbedded reservoirs are common in unconventional oil and gas development, yet the mechanisms of fracture propagation and deflection induced by interfacial shear stress during hydraulic fracturing remain poorly understood. To address this, a three-dimensional discrete lattice–fluid network coupled model was established and analytically validated to reveal the fracture propagation and deflection behavior driven by interfacial shear stress. The effects of formation dip angle and fracture initiation position were systematically investigated. The results indicate that under parallel stacking conditions, fractures exhibit regular double-wing propagation, and the dip angle has a negligible influence on deflection behavior. Conversely, in stacking configurations, the fracture deflection angle increases nonlinearly with the dip angle, rising from 3.7° at a 5° dip to 8.6° at a 12.5° dip. Fracture networks tend to propagate along the normal direction of the sandstone, a trend that intensifies at steeper dips. Interfacial shear stress is identified as the dominant mechanical factor controlling deflection by regulating the stress intensity factor ratio through the dip angle, thereby determining the propagation path. This study elucidates the mechanism by which interlayer dip angle differences drive mixed-mode fracture propagation via interfacial shear, and establishes a quantitative prediction model and a response-surface-based design chart for fracture deflection angles, along with optimized engineering recommendations, providing theoretical and practical foundations for multi-layer stacked reservoir fracturing optimization.
Maintaining load-bearing capacity while accommodating deformation and absorbing energy remains a challenge for metallic roadway supports in rockburst-prone coal mines. To address this need at the connection level, an energy-absorption joint (EAJ) incorporating patterned steel blades is proposed for U-shaped steel supports. Its static response is investigated through laboratory tests and finite element (FE) analysis. The experiments examine the effects of patterned material area and blade configuration, while the numerical study evaluates four configurations with blade thicknesses of 3–6 mm. Relative movement between the connected steel members induces blade stretching and plastic deformation, accompanied by inward bending of the cover plates. Experimental blade fracture is associated with an abrupt load reduction near the peak. The FE model reproduces the principal deformation pattern and peak-load ranking. Absolute errors in peak load and absorbed energy are 2.97–14.55
To address the current challenges of diagnosing fracturing interference types and the lack of an evaluation system for interference effectiveness in horizontal well groups in unconventional reservoirs, this study proposes a method for diagnosing and evaluating fracturing interference. Based on the principles of unconventional complex fracture modeling, the fracture propagation model is established. By simulating four typical fracture interference patterns—non-propagating fracture pattern, main fracture propagation pattern, branch fracture propagation pattern, and natural fracture connectivity pattern—the spatial distribution patterns of inter-well fractures are forward-modeled, and diagnostic criteria for typical fracturing interference patterns in horizontal well groups were developed. Based on the principles of pressure falloff well-test interpretation and considering the characteristics of inter-well fracturing interference, the interference well-test evaluation model was constructed. Inverse calculation of fracture parameters was carried out to analyze fracture propped effectiveness under different interference patterns and to clarify the impact of fracturing interference on the effectiveness of horizontal well groups. The proposed method was applied to a typical fracturing interference horizontal well groups in the Daniudi Gas Field, Ordos Basin, China. And its validity was confirmed by comparison with microseismic monitoring results. The study demonstrates that: The impact of fracturing interference on the stimulation effectiveness of horizontal well groups follows the order: main fracture propagation pattern > branch fracture propagation pattern > natural fracture connectivity pattern. Specifically, the main and branch fracture propagation patterns exert negative effects, reducing propped fracture volume by 7.2
