Multifractal properties of oil and gas indices in the Songnan Low Uplift of the Qiongdongnan Basin deepwater area

Recently, a high-quality reservoir was discovered in the Songnan Low Uplift in the eastern deepwater area of the Qiongdongnan Basin, northern South China Sea. To establish whether this area has good exploration prospects, this paper uses the multifractal moment method to analyse 2689 data points acquired from the basin in the SE of the southern low bulge. It is pointed out that the fractal behaviours of different types of geochemical indices are often distinguished by multifractal spectra of different shapes, therefore multifractal spectrum function analysis is used in this paper. These data were considered within the context of 13 oil and gas indices describing the multifractal spectrum function morphological characteristics. The results show that these indices can be divided into three types according to the multifractal spectrum. Indices with a strong multifractal spectrum function in the Songnan Low Uplift have the characteristics of a wide and continuous multifractal spectrum function, forming a right-skewed arc shape, while the other indices show weak or single-fractal characteristics. The results are in good agreement with principal component analysis results, where the spectral function of each principal component shows that the gas source of the C1, C2, C3, nC4, nCS, and heavy hydrocarbon indices in the Songnan Low Bulge has multifractal characteristics. The weight of these indices with strong multifractal characteristics shows that the principal components C1, C2 and C3, and heavy hydrocarbons, are important indices for delineating hydrocarbon prospects in the Songnan Low Uplift. Multifractal and spatial analysis techniques provide new ideas for index selection and comprehensive information extraction for oil and gas exploration.