Abstract: The structure of the reservoir in the BZ19-6 gas field metamorphic rock sub-salt dome is complex and diverse, with developed and heterogeneous fractures. Identifying effective fractures in reservoir evaluation is an urgent problem, which is important for the exploration and development of the gas field. The study mainly focuses on the granite gneiss and Archean intrusions with a small amount of intrusive rock as the research layer. The degree of fracture development of the research layer is identified by analyzing the R/S (rescaled range) of conventional logging curves. The development position of fractures is predicted by calculating the second-order difference of Lg(R/S). Furthermore, the R/S analysis results are compared with the statistical observation of thin-section fractures and the interpretation results of electric imaging to establish a classification standard for the degree of fracture development in granite gneiss reservoirs using the Hurst index. The study shows that: 1) The improved method of combining R/S analysis and Newton's difference method is feasible for fracture evaluation in metamorphic rock reservoirs and can identify fractures with a width greater than 0.005 mm. 2) The second-order difference value of Lg(R/S) curve can accurately identify the development position of natural fractures, and K-Rxo is positively correlated with fracture line density, with high correlation. 3) Rock anisotropy and fracture filling have an impact on the accuracy of fracture identification using the conventional logging curve R/S analysis method.