Directional control of fracture patterns by pore pressure–stress coupling in overpressured shales: Insights from the Dongying Depression

Pore pressure–stress coupling (PSC) is a geomechanical mechanism by which pore pressure changes drive stress reorientation and control fracture development. However, quantitative constraints on the directional control of PSC on fracture patterns in overpressured lacustrine rift basins remain limited, restricting reliable fracture prediction in deep shale reservoirs. This study integrates basin modeling, machine learning–based pore pressure prediction, rock mechanics experiments, and poroelastic stress modeling. The Es4–Es3 interval of the Shahejie Formation in Well NY1, Dongying Depression, Bohai Bay Basin, is used to investigate overpressure evolution, present-day stress state, and the controls of PSC on fracture patterns. The results show that (1) the upper Es4 member (Es4U) experienced two episodes of hydrocarbon generation-driven overpressurization during the Paleogene and Neogene, and the predicted present-day pore pressure (55.3 MPa) agrees with the measured value (55.0 MPa); (2) the present-day maximum horizontal stress is oriented approximately E–W, as determined from Formation Micro Imager (FMI) logs and supported by regional World Stress Map (WSM) data. Poroelastic modeling constrained by density logs and rock elastic parameters indicates a predominantly strike-slip stress regime ( Aϕ = 1–2), with normal faulting and reverse faulting states identified in individual intervals; (3) under strike-slip, normal faulting, and reverse faulting stress states, PSC preferentially promotes vertical, high-angle, and low-angle fractures, respectively. FMI-measured fracture populations independently support this prediction, with mean dip angles decreasing systematically from 49.5° (strike-slip) through 46.3° (normal faulting) to 33.7° (reverse faulting). This systematic decrease reveals a directional control of PSC on fracture patterns. By integrating reconstructed overpressure evolution, present-day stress states, poroelastic PSC modeling, and FMI-based fracture statistics, this study establishes a quantitative link between PSC and fracture orientation under different stress regimes in an overpressured lacustrine rift setting. These findings provide geomechanical constraints for fracture prediction and geomechanical modeling in deep overpressured shales.