A Study on the mechanisms, prediction, and pressure influence of bedding fractures in deep shale

The degree of bedding fracture development in shale oil reservoirs directly affects reservoir storage capacity and fluid flow capability. However, the genetic mechanisms of these fractures remain poorly understood, and their relationships with formation pressure and productioninduced pressure drawdown are unclear, hampering the optimization of sweetspot identification and development strategies. In this study, using welllog data and core observations from multiple overpressured horizontal wells in a faulted lacustrine basin in eastern China, we apply the ΔlgR method to estimate total organic carbon (TOC) content, employ R/S rescaled range analysis to compute second derivatives of logging parameters for enhancing fracture responses, establish a prediction index Q for bedding fracture density, and adopt the organicmattercorrected Eaton method to derive the formation pressure coefficient. The influence of bedding fractures on formation pressure and production drawdown is also examined. The results show that: (1) Sensitivity analysis identifies gamma ray (GR), acoustic transit time (AC), compensated neutron (CNL), density (DEN), resistivity (RT), and TOC as sensitive parameters. The predicted index Q correlates well with coreobserved bedding fracture density, yielding an average match rate of 80%. (2) Bedding fracture development is predominantly controlled by hydrocarbongeneration overpressure, with lamina interfaces serving as natural mechanical weak planes, and is jointly governed by lithology, organic matter content, and lamina texture. (3) Bedding fracture density is positively correlated with the formation pressure coefficient; when the density exceeds 15 fractures/m, the pressure coefficient is generally above 1.4 and its increase tends to level off. (4) Under comparable fracturing and production conditions, areas with high bedding fracture density exhibit a relatively low pressure decline rate at the early development stage, whereas areas with low density show a more rapid pressure drop. (5) Highdensity areas not only develop complex hydraulic fracture networks but also provide more favorable conditions for proppant placement, enhancing the fracture system's resistance to closure under confining pressure and thereby effectively retarding reservoir energy depletion.