A geomechanical framework for deciphering the formation mechanisms and multi-stage differential distribution of fault–fracture systems

• Multiphase tectonic stress evolution is integrated with geomechanical modeling to explain fracture development in tight sandstones. • Finite element simulations are used to quantify the spatial distribution of paleo- and current in-situ stresses. • A multiphase superimposed fracture criterion enables quantitative fracture prediction and reservoir evaluation. Understanding the formation mechanisms and differential distribution of fault–fracture systems across multiple tectonic stages is essential for fracture prediction and efficient development of deep tight sandstone reservoirs. In this study, a geomechanical framework is established to investigate fault–fracture evolution under multi-stage tectonic superposition. Core observations, thin-section analyses, and well log interpretations are integrated to characterize the geometry, occurrence, and genetic types of tectonic fractures. Paleo-stress fields for successive tectonic periods are reconstructed by combining regional tectonic constraints, fracture orientation statistics, fault kinematic indicators, and inverted mechanical parameters. Finite element numerical simulations are then conducted to quantify the evolution of paleo and present-day in-situ stress fields, considering boundary conditions, mechanical heterogeneity, and uncertainties in stress magnitude. A key innovation of this study is the refinement of rock rupture criteria and the development of a multiphase superimposed fracture criterion, which incorporates stress inheritance, cumulative damage, and mechanical reactivation effects. This criterion enables quantitative prediction of fracture orientation, intensity, and spatial distribution under complex tectonic superposition. The results show that the latest tectonic stage is characterized by pronounced zonal stress variations along EW-, NS-, and NE–SW-trending fault systems, with significant stress concentration in areas affected by multi-stage overprinting. Fracture development exhibits a sequential evolution from early EW-oriented fractures to composite fracture networks involving NE–SW and NS orientations. This study provides a practical, geomechanics-based approach for predicting fracture distribution and optimizing reservoir development in deep tight sandstone reservoirs.