A Statistical Method for Lithic Content Based on Core Measurement, Image Analysis and Microscopic Statistics in Sand-conglomerate Reservoir

Abstract

The type and content of lithics are of great importance to reservoir research. The existing statistical methods for lithic content mainly focus on sand-level lithics, failing to consider gravel-level lithics. Thus, these methods are not applicable to sand-conglomerate reservoirs, where sand-level and gravel-level lithics coexist. To solve the defects, this paper proposes a hybrid strategy for lithic content in sand-conglomerate reservoirs. Firstly, the type and content of gravel-level lithics were determined through full-bore formation microimager (FMI) imaging logging and core analysis. Next, the type and content of sand-level lithics were obtained by thin-section observation. On this basis, the data on the two levels of lithics were integrated to yield the total content of each type of lithics in the sand-conglomerate reservoir. The hybrid strategy was applied to analyze the lithics features and physical properties of a sand-conglomerate reservoir in the upper part of the fourth member of the Shahejie Formation (upper Es4), north zone, Dongying Depression, China. The results show that the hybrid strategy output greater upper and lower limits of the total lithic contents than the existing methods, and outshined the traditional thin-section observation in accuracy. In the study area, the sand-conglomerate reservoirs in the upper Es4 of the two blocks have different physical properties. The difference is mainly attributable to the different types and contents of lithics of the two blocks. The proposed strategy boasts a strong application potential in oil and gas exploration.