Abstract:

The mud shales of the second member of the Paleogene Funing Formation in the Gaoyou Sag of Subei Basin are distinguished by their complex pore structures, well-developed bedding, and pronounced heterogeneity. These characteristics complicate the accurate evaluation of pore and fluid types using conventional well logging techniques. However, two-dimensional nuclear magnetic resonance（2D NMR） logging presents distinct advantages in fluid identification. The study incorporates the “Blind Source Separation” signal processing technique to perform data clustering analysis. Subsequently, a fluid zone model is applied to determine the fluid content with different movable properties in the reservoir space of the Huazhuang area. The findings demonstrate that 2D NMR logging significantly improves the accuracy of reservoir fluid evaluation, yielding reliable estimates of total porosity, effective porosity, oil saturation, and movable oil volume content. When compared to core analysis, the average absolute errors for effective porosity and oil saturation are minimal, at 0.4% and 7.3%, respectively. Further analysis of fluid properties within the primary lithologies of the second member of the Funing Formation reveals that the felsic-calcitic-dolomitic-mixed shales possess superior physical properties, oil volume content, and mobility. These characteristics render them as prime targets for shale oil exploration in the region. The successful application of 2D NMR logging in the Huazhuang area not only addresses the challenges associated with evaluating shale oil porosity and saturation but also provides essential insights for selecting “sweet spot” districts and forecasting reservoir production.

Key words: Subei Basin, Gaoyou Sag, 2D NMR logging, shale oil, fluid identification