The effects of sedimentary facies and diagenesis on pore structure: in the sandstones of Paleogene Formation of Nanpu Sag, China to be more representative to the results and discussion

The pore structure of sandstone reservoir, primarily influenced by depositional parameters and diagenetic features, is crucial for petroleum engineering and petrophysics. Core analysis shows that samples from different sedimentary micro-facies can be grouped into distinct areas on a cross-plot of porosity versus permeability, and submerged distributary channels facies have the best pore structure, followed by river mouth bars facies, distal bar/blanket sand facies, and bay facies. In order to quantitatively characterize the influence of sedimentary microfacies and diagenesis on pore structure, seepage factor f (slope of the line through ( \(\phi\) $\varphi$ , \({\text{Log}}_{10}\left(K\right)\) ${\text{Log}}_{10}\left(K\right)$ ) and ( \({\phi }_{max}\) ${\varphi }_{\mathit{max}}$ , \({\text{Log}}_{10}\left({K}_{max}\right)\) ${\text{Log}}_{10}\left(K_{\mathit{max}}\right)$ ) on porosity–permeability cross-plot) and diagenetic indictor C_d (relative value of f value to the center of the f range) are introduced to quantitatively characterize the effects of sedimentary micro-facies and diagenesis on pore structure, respectively. Results show that the smaller the f value, the more favorable the sedimentary micro-facies are to reservoir pore structure. And within a specific distribution range centered on f, the larger the C_d value, the more favorable the diagenesis is to reservoir pore structure. Application results are consistent with petrographic features from core analysis, which indicates that the method is effective. This method provides a quantitative characterization method of the mapping relationship between macroscopic geological and microscopic pore structure, and can be effectively applied to reservoir analysis and pore structure characterization.