Multi-level division method of flow units for accurate permeability assessment of glutenite reservoirs:A case study of reservoir W53 of Paleogene Wenchang Formation in Lufeng oilfield

The glutenite reservoirs of the Paleogene Wenchang formation in the Lufeng oilfield in the eastern South China Sea are characterized by complex lithology,low porosity,and strongly heterogeneous pore structure.Since different types of reservoirs show greatly different seepage characteristics,traditional permeability models are difficult to meet the demand for petroleum production and development due to their low calculation precision.Flow units can effectively characterize the internal seepage characteristics of reservoirs.However,the division of flow units based only on flow unit indicators will lead to misclassification.Given the macro and micro hierarchical heterogeneity of reservoirs of the Wenchang Formation,this study establishes a multi-level division method of flow units by combining geological,logging,and core data.Specifically,the first-order flow units are determined according to sedimentary facies.Then the second-order flow units are determined according to the lithology identified by calibrating conventional logging based on core and imaging logging.Finally,the third-order flow units are determined using flow zone indicator (FZI) approaches combined with pore structure.In this manner,a three-level division method of flow units based on sedimentary microfacies-lithology-pore structure is formed.As indicated by application results,this method can effectively avoid the inaccurate classification of flow units and improve the accuracy of permeability calculation,thus having great significance for finding high-quality reservoirs and the efficient development of oil reservoirs.