Since carbonate reservoirs characterized by diverse reservoir spaces and high heterogeneity exhibit intricate internal pore structures,conventional petrophysical classification methods fail to accurately classify these reservoirs,especially the reservoirs with complex porous systems whose pore throat radii manifest a multimodal(e.g.,bimodal,and trimodal) distribution.By investigating the M Formation's carbonate reservoirs in an oil field in the Middle East,this study clarified that the internal pore structures of rocks determine the pore throat radius distribution,which in turn affects the classification of rocks.Hence,starting with the pore throat size distribution,and considering the contribution of pore components corresponding to each peak in the multimodal samples to the rock reservoir space and seepage capacity,this study proposed a pore throat radius parameter Rmax* combining pore throat sizes and their proportions to characterize the pore structures of rocks based on the cumulative permeability curve.Then,this study classified the selected 114 bimodal and 43 trimodal rock samples.Moreover,the characteristics of each type of reservoir were examined in depth by combining with physical properties,mercury injection data,thin-section observational data,and logs.The results of this study show that Rmax* can better characterize the pore structures of reservoirs and improve the reservoir classification effectiveness compared with the classification based on a single pore throat radius(R35,corresponding to mercury saturation of 35%).
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