Fracture identification and evaluation of metamorphic buried hill fractured reservoir using image log data in Bozhong A gas field

Accurate fracture identification and evaluation are critical for characterizing metamorphic buried hill reservoirs, which exhibit strong heterogeneity and complex pore-fracture systems. Traditional methods often rely on single fracture parameters, which inadequately capture overall fracture effectiveness and reservoir quality. This study integrates conventional and image log data from the Bozhong A gas field to analyze fracture development and establish a robust, multi-parameter fracture effectiveness index (F i ). The index synthesizes fracture width, porosity, linear density, and the angle between fracture strike and maximum horizontal stress, with weighting coefficients determined based on correlation with test production. Results show that fractures are best identified using resistivity ratio, sonic interval transit time, bulk density, and neutron log. The derived F i strongly correlates with production data and classifies reservoirs into three types: Class I (F i > 0.3), Class II (0.2–0.3), and Class III (0.15–0.2). Applied to reservoir evaluation, this index effectively discriminates high-quality reservoir intervals in the study area. This proposed multi-parameter index facilitates a well-specific quantitative evaluation of fracture effectiveness, and provides a more reliable and holistic tool for fracture and reservoir assessment compared to traditional single-parameter criteria.