Reservoir quality evaluation of tight carbonate gas reservoirs using fractal–multifractal pore-structure metrics: a case study from the Taiyuan Formation, Ordos Basin, China

Résumé fourni par la source

Abstract Tight carbonate gas reservoirs commonly contain appreciable storage space but highly variable flow capacity, making reservoir-quality evaluation and favorable-interval screening challenging in exploration and development. This study investigates 10 representative limestone core samples from the Taiyuan Formation, Ordos Basin, China, using high-pressure mercury intrusion data integrated with segmented single-fractal and multifractal analyses to identify pore-structure metrics relevant to reservoir evaluation. The results show that the pore systems exhibit segmented fractal characteristics: the low-pressure fractal dimension $${D}_{1}$$ is more sensitive to the development of fracture-related macropore pathways and may therefore be associated with seepage potential, whereas the high-pressure fractal dimension $${D}_{2}$$ mainly reflects the roughness and complexity of matrix-controlled storage pores. Furthermore, multifractal parameters provide a quantitative description of the overall heterogeneity of the pore system. The spectral width ( $$\Delta \alpha$$ ) reflects the intensity of heterogeneity, while the asymmetry index ( $$R$$ ) helps distinguish whether the pore structure is more strongly influenced by large seepage pores or small storage pores. When combined with pore-throat attributes and multivariate classification, these metrics divide the reservoir into three resource-quality classes and suggest that intervals with high $${D}_{1}$$ , positive $$R$$ , and moderate $$\Delta \alpha$$ are more favorable pore-structure conditions for fluid mobility. The proposed workflow therefore provides a preliminary pore-structure-based framework for reservoir-quality evaluation and favorable-interval screening in tight carbonate gas reservoirs.

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